Siglent SDS1x04X-E BodePlot II (SFRA) features and testings

[rf-loop]

If you comment in this thread, please only things about BodePlot II in SDS1x04X-E models.  There is lot of topics for other things with this scope! And if not, make new.



I will show here some of my tests and observations about Siglent new BodePlot version II for SDS1104X-E and SDS1204X-E.
(BodePlot is also known as FRA or SFRA, Sweep Frequency Response Analysis).

New version (II) is so advanced in this price class that it is best to introduce in separate  thread what handle only BodePlot version II and nothing else.


I will soon but slowly collect here some tests, details etc, depending how I have time and how do my outworn eyes condition allow.

-----------
Previously there have been BodePlot version I.
New Bode Plot II  is first time published with FW 6.1.33
Imho it is really big step to right direction.

There is some new functions and also many other improvements. It is more like totally new design, not like "facelift".

BodePlot II is now an amazingly good and versatile tool especially considering the Price Range.
I have also feel that they will still develop it better later.

Although it is astoundingly good it still needs some finishing and UI fine tuning to improve operating ergonomics. Yet, even if it were not developed any more, it is a good real tool.

It is not just an extra line to the sales brochure. It is a real tool with significant real value. But it need Siglent Signal generator.

BodePLot II have same basic limits as also first generation BodelPlot.

SFRA max frequency range is 10Hz - 120MHz (or less if used Siglent generator max is less).
With its frequency selective detector and automatic Channel Gain system it have well over 110dB max dynamic range.
 
1 channel for phase reference/DUT input level reference. (user can define what channel is for this)
3 channels for DUT outputs with Phase and Amplitude. (user can define channels)

Minimum span is 500Hz and maximum full available frequency span.
In Linear (step) sweep mode it can use 10 - 500 data points for span in use. (with 500Hz min span, 1Hz step)
In Linear step sweep mode user set center and span and steps in this span.

In Decade (log) (step) sweep mode it can set for 2  - up to 275204396* points/decade what can give up to ~500pts for used span. In this mode user set start and stop frequency and points/decade.
*with higher frequencies and narrow span this points/decade value is big. Just select "max" using virtual panel and you have around 500 points with this frequency span.


It can run in two modes.
Channel Gain:Auto mode ( more dynamic range specially over ~100kHz. Slower sweep than with Hold mode. It automatically continuously adjust scope input V/div   setting (using also fine adjust) during sweep, depending DUT output level, for optimal result)
 
Channel Gain:Hold mode (faster but max dynamic range is less, this mode keep channel V/div settings constant (remember first adjust best V/div so that signal do not clip in any point (for manual setup I recommend max 8div p-p for better level accuracy)

Sweep mode can be Simple (constant level) or Variable level. In variable level mode it use user defined table for sweep level profile. Profile can have max 10 data pairs, for freq and level. Between table points do linear interpolation for levels.

It need perhaps BodePlot II  User Reference Manual  (not these simple nonsense User Manuals). Except that after every FW it is obsolete..
There is so many things, what may confuses an inexperienced user, or if experience is from different device and imagines it to work like another. Of course it can be used with a try-oops-try method but many times it leads to frustration and then barking that it works wrong.
 
But, as told, there is also things what Siglent need develop better and also fix some bugs.

In all my tests and comments things are based to SDG1032X/62X using with SDS1x04X-E. (with this I can not do tests up to 120MHz)
SDG FW version 01.01.33R1
and oscilloscope  FW 6.1.33

About dynamic range. There is not clear simple answer. It depends..
If think DUT what do not have  signal amplification answer is bit more simple.

Example if use SDG1062X and whole bandwidth 10Hz to 60MHz.
BP II maximum setting for SDG level is +19.5dBm. (6Vp-p to 50ohm)
But SDG1000X  can not this over 10MHz. (Under 10MHz it can around +24dBm but BodePlot can not set this, max is 19.5dBm)
SDG 1000X maximum over 10MHz is +17.96dBm (5Vp-p to 50ohm)

Now, if with these facts and when DUT can only attenuate 0 or more we can use roughly up tp 110dB dynamic range when over 100kHz. Using 17.9dBm input it is better say that dynamic range is 100dB
(there is some frequency what may have noise level is down to -120dB (ref 17.9dBm as 0dB) but base noise level is not constant and in worst places it is near -100dB, in this test Ref go ti Ch1 and Ch2, 3 and 4 terminated.)

Note: Under 50kHz~100kHz frequencies dynamic range is less and bit weird, later about this.. Also displayed base noise level do not correlate this. These tests take time when use full resolution and I want keep the testing accuracy at a somehow good acceptable level. Also it is more complicated what I initially thought, so I need carefully think what and how I test. Also with full resolution and over many decades one sweep take time when run it in channels gain auto adjust mode.).

Here images
10Hz - 100kHz and 10kHz to 60MHz (ref 17.9dBm ref 0dB)
Signal (DUT in/reference Ch1  17.9dBm, Ch2, 3 and 4 terminated except positions where 0dB attenuated reference signal connected to  channel for check level)





How fast it do these. When all three DUT out channels are on and channel Gain Auto mode and Log sweep and max freq resolution. Both of these BodePlots takes over 20 minutes.

Of course now when channels can adjust gain automatically and if signal level is higher also dynamic range rise. But in turn if need use lower level reference/DUT input signal it also reduce available dynamic range, noise floor stay in its position.
And then if want use fixed channel gain (Channel Gain Hold)  of course then this kind of dynamic range is not available at all. (I will show some tests later but now need find some accessories after accidentally burned some terminators and step attenuator  )

Example if there is selected 10mV/div. Abs max signal level is ~100mVpp  and in practice better stay <80mVpp. Now attenuate it 40dB. What you can see. Just do not use fixed (channel gain Hold mode) if need maximal possible dynamic range. There is noise and there is 8bit ADC. (I do not know what method Siglent use for pick up signal out from noise but it looks like there is some method in use(?)  in BP II.




Here two BodePlot images -- not as I want do it (due to my burned step attenuator)  but also with these it can somehow see.


Channel Gain:Hold mode


In this image channel gain is in Hold mode. I have adjusted levels so100Hz give good visual level on screen and stay in most linear range.
It can see that (of course) around -40dB it goes to troubles. Signal is these so small. Still it can detect phase but with eyes if look normal YT display can not see "nothing" but reference signal and Ch4 around straight line and signal barely visible if know what to look. (If use example over 64 trace average there can see just around one bit (on screen 2 pixel) height rectangle duty depending about small posssible offset)

And then corresponding  YT images from 100Hz and 800kHz


Here is YT image with same setup when freq is start point 100Hz



This YT image is in same setup when freq is 800kHz. As can see - what you can see...
if voltage is divided by 100 it means 40dB drop. Look BodePlot, dynamic range is very limited.
We have 8 bit ADC. Can you use every single bit. No, you can not. This is real world, not from ideal world what do not exist.




Channel Gain:Auto mode


In this image channel gain is in Auto mode. When it sweep and signal drops it also rise sensitivity using fine steps. (as can see in image where it have reached 2.06mV/div when signal is attenuated ~55dB so it can see well.

And then corresponding  YT images from 100Hz and 800kHz


Here YT image how it is in 100Hz sweep start point when BP2 have adjusted levels automatically.



It looks like this when frequency is 800kHz and BP2 have automatically adjusted levels.
During sweep it continuously watch and adjust levels. Here can see level is roughly 4div height p-p and level related to reference can easy measure, visually roughly -55dBref as can see also in bodeplot (and of course phase)

With this method it can reach relatively high max dynamic range with basic 8bit imperfect ADC.

With higher frequencies, for more accurate phase.
You need compensate setup cable delays and channels skew.




note: some image names have error
BP2-ChannelGainAUTO-RC-LP-100k-1MHz
BP2-ChannelGainHOLD-RC-LP-100k-1MHz
100k is wrong and need be 100Hz

[rf-loop]

Here is some kind of partial "menu map" for BodePlot II main functions and settings.
Not including all details and settings.

Also one note for better use.

If you have Siglent signal generator what have two identical output channels.
(example SDG1000X, 2000X and so on)

For better performance with higher frequencies over audio range frequencies up to BodePlot II maximum.
Set generator for zero phase shift and zero delay and zero level shift channel tracking mode. So that Ch2 follow Ch1.

Take Generator Ch1 to BodePlot reference input (in scope menu reference input  is named as DUT input) default is scope Ch1 but you can also select other Ch.)

Take Generator Ch2 to DUT input and DUT output to oscilloscope DUT output channel (default is Ch2).
Also take care about signal pathways delays. They need be equal (cables travel time)  for better Phase accuracy.
Note: If need best phase accuracy then it is best to use same ADC channels for DUTout and DUTin/ref. Ch1/Ch2 pair or Ch3/Ch4 pair.

If you have one channel generator or if you just want use one  generator channel setup or 2ch generator what do not have enough accurate tracking outputs and/or if you work with low frequencies  you can split (even with simple T-split) this generator output channel to DUT input and BodePlot reference input channel ( in scope menu it is named DUT input)
In this case impedance matching is bit more difficult and so on but no problem with very low frequencies.
Naturally if you have real "calibration grade" splitter and set of cables, feed thru terminators etc it can do well but this kind of splitter have many dB power loss.
Of course in simple cases and with high impedance systems you can also use normal probes but as we know 1x probes freq response is what it is and so on and so on.
If BodePlot get garbage in its output is also garbage. So it is good practice first make test run also with null DUT just for your reference and for check cables/probes setup is ok. 

Here BP II simplified menu map.  (1500x2200 png)
Too big size for display in forum but you can download it for full res.




How to connect signal generator, DUT and oscilloscope (two connection principles (picture)).

If you do sensitive measurements (and specially with low frequencies). Take care oscilloscope self-calibration is fresh. Before BP it is best to keep oscilloscope running 30 minutes for thermal full equilibrium. Shut also Quick-Cal off (utility menu). If you use SAG1021 generator run also zero adjust procedure before use BPII.
Also if you do very sensitive tests with high accuracy needs, IF possible, select signal level so that during test it do not cross over voltage bands in your dynamic range needs is not high.
Voltage bands:

Code: [Select]

I     500uV/div - 118mV/div. 
II    120mV/div - 1.18V/div.
III   1.20V/div -   10V/div.
When during sweep  automatic variable gain cross over relay selected voltage band there may exist tiny step error/glitch in amplitude and/or phase.


There is two main methods. Using single channel generator for reference and DUT input or using two separate channel.  Before start BodePlot with two channel generator method user need set generator so that channel 2 is tracking channel 1 (same phase, same freq, same level). After this setting done in SDG then use BodePlot just normally and set "stimulus" level as need. In two channel method image default DUT is 50ohm I/O device.
Note that in BodePlot there is two methods fore measure dut level things. Vout/Vin and Vout. User need think which one is better to use. Two channel method system look Vin  what is now not same as DUT in specially if there is poor impedance matching and reactive DUT input. Also with one channel method user need take care about impedance matching and carefully think possible differences between scope DUTin/reference channel level and real DUTinput level. Low frequencies, audio etc, are not so critical.





As can see  in "Config" menu there is selections what I have marked with numbers 5 and 6.

Usually we use Sweep type "Simple" (5). It is also factory default.
This sweep type use constant user defined generator output level (defined in "Stimulus" menu).

Other Sweep type is named "Vari-level" (6)
User can define how generator output level change during sweep. User can make this frequency-level profile. There can set 4 separate profiles, A, B, C and D. Each profile have 2 - 10 nodes. Every node have frequency and level. First node is sweep start and last node is sweep end.
Between nodes system use lin/log interpolation for level. On the screen line is straight independent of if your selected horizontal scale is logarithmic or linear.

Before user can find all settings and how to make profile it may need some exercise.
Best practice with profile node table is imho. First think what is your sweep end frequency.
Open Edit and set it for 2 nodes. Edit this 2 for wanted end frequency. After then select how many nodes you want. When you turn selection from 2 to 10 it copy this 2 to all nodes from 2 to 10.
Why this. There is one principle. Lower node number can not have higher frequency than next node.
After then you can turn start freq (node 1) how you want and its generator output level level.
Then next node and next and so on. If you find you do not need all 10 nodes then just reduce these last nodes what do not need. Turn adjust knob carefully. If you remove too many then you need edit these again.
In Vari-level mode if you open "stimulus" menu there is not level selection (aka "Stimulus"). (your level selection is in this table)
But there you can select what units you use, Vpp. Vrms, dBm and so on, also system load impedance. If you have real load 50 ohm then use it. If your real load is example 600 ohm then select it. Only when set value  and real value match then measurements and scales can be true.

/example images/


I will update later some more details here.

[rf-loop]

Here  some kind of dynamic range test.
Why 455kHz.
Because this is one very common IF filters frequency range and with these filters need enough dynamic range because stop band is important, least for me - as old "radio man".

Of course also other frequencies are important but as can see in some previous image where is base noise over 10Hz to 60MHz there can not see extremely bad things.
I will make later more deep tests about dynamic range but due to lack of time and also due to fact that these tests takes long time when also want somehow trusted results - tests are now under work. Also it is somehow possible that later some FW change these things, specially what I have found under ~100kHz frequencies.
I think it is not really wise to talk about dynamic range if we do not define this level what is our reference level where from we count dB's. In some Keysight data sheet they use reference level 0dBm.  If use example Siglent BPII max set value  for generator it is 19.5dBm. From this level it have up to >110dB dynamic range. If there also can exist amplification and due to this DUT output is also over its input, then dynamic range can be even more. But then, whole range is not usable over whole 10Hz - 120MHz frequency range.   So it need carefully think how we talk about dynamic range.  Data sheets have very limited information about these things. Even Keysight higher end models data sheet, what I found, about BP are totally poor and leave many many open questions. So I do not know how to tell these so that things are comparable.

It need also note that channels cross talk is quite low (in this price range least good).
Also  mostly with this kind of work need just one channel. And if select reference(Dut in)  Ch1 and DUTout Ch4 then also reference cross talk is quite low to DUT out signal channel (distance to Ch4 os more than defaul DUT out Ch2)
Note: If need best phase accuracy then it is best to use same ADC channels for DUTout and DUTin/ref. Ch1/Ch2 pair or Ch3/Ch4 pair.




1. First test setup. Generator output level 18dBm from both channels. (Gen Ch2 is set for tracking Gen Ch1)




2.G Ch1 to scope Ch1 (50ohm term) as reference, Ch3 no signal, 50ohm termination (base noise) and G Ch2 to scope Ch4 via hp step attenuator set and 50ohm feed thru in scope input.




3. Same as 2. but attenuation changed between 0 to 120dB




4. This is how it looks in normal YT display.  Reference 18dBm, attenuated 110dB (Ch4) and empty terminated channel (Ch3)  (do not care this small ~<100uV internal dcoffset. It is fully nonsense. If internal offset DAC is 16 bit it means roughly 1-2 step)





5. One example about Data table. And with this table I can see all steps from 0dB - 80dB is very close (more like +/-0.1dB).  -90dB and -100dB still something like  +/- 0.3dB or better and then  -110 dB  is clearly less accurate (noise) +/- 1-2dB. (but if estimate average it is still perhaps inside +/- 0.5dB. Of course these are not absolute accurate.


Reference 18dB may drift bit, then step attenuators repeating accuracy, steps tolerances etc (exept that these are really good ones and I do not like use these for this kind of "try this and that-oops" things)

All cables (exept inside attenuator package)  RG223 (better shielding for keep external noise out)

As can see, this BodePlot II  is "bit better" than.....not just only checkbox feature in sales advertisement.



Now we can think some amazing numbers what you see in these pictures.
If you want simple calculator this can use:
https://www.analog.com/en/design-center/interactive-design-tools/dbconvert.html
Note if you are not familiar with these: Vpeak (Vp)  is not Vp-p (Vpp) 1Vp (Vpeak) is 2Vpp (V peak to peak).

Lets take first this 18dBm signal (18dB over 1mW, 0dBm is 1mW).
How much it is if think voltages (system is now 50ohm)

Signal what go to attenuator and is DUTin/ref is of course sinewave. 18dBm  is 2.51Vpeak, 5.02 Vpp
(This is why ChannelGain Auto adjust it around 1V/div with this level)

Now there was 110dB attenuator as DUT. After attenuator there is -92dBm (18 - 110)
How much -92dBm  is in the scope normal YT display if think peak to peak height.  It is  15.9uVpp

And as can see it can go even more low least in some frequency bands if you look this topic first message first two images (noise level) and then in this message (Reply #2)  images 2 and 3.

Siglent most sensitive setting is 500uV/div what is rare in oscilloscopes but now this BodePlot II takes all out from it and even more. If think 500uV/div and if ADC is ideal 8bit its range roughly 5000uV (5120)
it means ADC one step is 20uV. How it can measure 15.9uVpp signal and even less.. 






 
How Siglent did it. I really do not know (If I guess something, perhaps it explain why it is bit slow sweeping, specially when ChannelGain Auto mode is used).
I can only say - astounding.


But next two test images (there is more but I think this is enough for guessing and may give some tip...
(frequency selective receivers what listen only DUTinput/Ref frequency  in DUTout signal channels.)

For this test there is two totally independed and totally unsynched generators. One run normally in BodePlot control and one is separate generator what do not sweep at all.
There is one test with 120kHz carrier with AM modulation. Mod depth 20% and Mod req 10kHz signal and one with just 3MHz 10dBm carrier.

This test nearly proof that they use "freq selective" method what listen only this frequency what is DUT input/ref frequency from BodePlot controlled generator when it step sweeps (something like SA with tracking generator).  This also explain better (one side) about how it can measure so weak signal from DUT. Even when it is barely visible when input is 500uV/div and averaged 1000 times (image 4).
But this can not use for superheterodyne receiver testing/fun-playing between example antenna and IF freq. Because it do not listen other than sweep Generator freq... seriously.. no matter.
But, alone this, imho, can not explain how it goes with 8bit ADC to these small levels.
They must do something more for enhance vertical resolution.
When take all sensitivity and resolution out from BodePlot II  it is slow. Of course if not want all out from this it can set for more fast (set less resolution, Channel Gain Auto off (Hold mode) and so on.)



Special test setup for images 6 and 7. (this is how you DO NOT normally use BodePlot.)

Special test setup for images 6 and 7. (this is how you DO NOT normally use BodePlot.)
Numbers as in image 7 test. Image 6 test 3MHz carrier no modulation.




6.  DUT out signal (Ch4) is not at all from DUT input signal. It is 3MHz 10dBm carrier from separate generator



7.  DUT out signal (Ch4) is not at all from DUT input signal. It is 120kHz AM modulated signalfrom separate generator. Mod depth 20% and freq 10kHz.  There can see these frequency slices what it use.
Of course this is not SA. These images only give information about how this Siglent BodePlot II works. (Note: freq slices size also depend used freq and span and steps etc.)

I like it even if it's not perfect and even when it have some "bad manners". Now I'm not anymore sad after I long time ago sold out my old R&S lady SWOB. This is far better. As long as do not need more than this freq range.

[rf-loop]

More about dynamic range (my generator what I can use at this time for this have max freq 60MHz)


Picture 1
Test setup in next image (dual channel generator setup for 50 ohm system).

Made many tens of test sweeps using different attenuations etc for
produce final estimate about level/dynamic range. Also changed 0-11dB attenuator unit in atytenuator package after all previous tests (I found it was unreliable, some internal contacts not reliable)

It is difficult to talk BodePlotII dynamic range itself because it depends input/reference level and it adjust channel gain automatically. But then there comes also channels cross talk. When reference level high it can also see in channels what measure DUT output(s)

As we know oscilloscope have wide range V/div settings. From 10V/div down to 500uV/div. Think 10Vdiv. If take 63Vpp (6div p-p) signal in 50ohm system it is roughly 40dBm.
Then if go down to 500uV/div and again 6div p-p  it is 3mVpp. Level is now -46.5dBm
But it can easy go down to 63uVpp and now it is around -80dBm. It can go even more low. Freq area where is example typical receivers IF filters it can easy go to -90dBm and it is 20uVpp. It can go  even more down, to 10uV/div,  when ref is 0dBm but in this case there is lot of noise and there is not available average what can delete some amount of noise.


When think dynamic range it also good to remember that ADC is here 8bit.
If we have ideal theoretical 8bit ADC,  what do not exist at all in practice, whole range is 48dB
16bit ideal ADC can give 96dB range.

So, here is one of first preliminary result.


Picture 2
This result is based to set of tests using 0dBm reference signal/DUTin signal and DUT in tests can see in Pic 1.  Channel Gain: "Auto", Display Amplitude mode is "Vout". Sweep 100Hz - 60MHz. 43 points/decade (give 250 data points for whole sweep. (if use max then it give 500 points but it is slower and do not give any more info for this kind of tests.. Also I have all BP sweeps data.csv where from is easy to check measured levels in every point and also it can recall back to scope BPII and all is displayed as in original BP sweep. In stop mode BP can also pan and zoom vertically and horizontally if need.)
In image there is also marked SAG1021 and SDG1000X these max levels what can use under BodePlot II control.
Naturally if your DUT have example amplifier or what ever what rise level over these limits it is possible and BodePlot II Channel Gain Auto leveling take care about it. In this image 40dBm (50ohm system) is just for give some tip. 40dBm is of course 10W (bit over 6.3div p-p  in oscilloscope screen with 10V/div range (1x)). 40dBm to -90dBm (130dB) is quite a lot.


Next here is example what do not push it to dynamic range limits at all but still good example about performance. Many entry level price scopes with BodePlot can not do this, not even close.
But frequency resolution is pushed to its limits. ~1Hz step is bit too rough for this. This down peak is so steep and sharp. Even more if resonator loading is optimal - now it is not.


Picture 3
I hope Siglent improve this data table frequency column resolution, for example Hz.. (example there is well enough room for all digits down to Hz, even when frequency is maximal 120.000000 MHz and even if use dot and kHz or MHz.
It can do it because it can send this frequency command to generator with full resolution, even using under 1milliHz res)
As can see in data table.


Picture 3a
This data is always bacround behind image when you run BPII and look BPII traces, independent of if you open and look this "List" or not. Displayed "List" is reduced resolution from this full data in BPII acquisition memory. This full resolution is what you save when you save it to USB flash. This can recall also back to scope and scope show this old BodePlot just with full details and for further analyze with scope if need. So, if you do some serious work, saving these is even more important and useful than just screen capture.
(BTW, previously max was 501 data points, now there is 500. Previously one step was 1Hz when use 500Hz span. Now step is 500/499 Hz. Why they change this. If want 100 steps it need 101 points...Siglent!!!....






Also it need draw trace even when there is 1Hz wide peak and not reduce it depending its neighbor points or least user selectable smoothing on/off. (I know it do this "noise reduction". It can see if carefully watch example how it draw base noise trace when it is doing sweep with high freq resolution. In some (rare) cases it is nice if this "smooth" can turn off.



Picture 4

BodePlot is based to internal data table. They call it as "List".
If part of draw is out of screen you can shift vertically up and down or change vertical scale scale. All data is there, even if it is out of display. This can do in Display Amplitude menu in BP Run mode or BP stopped. (When it is stopped, also horizontal scale can adjust, even change display between lin and log.)


Attached also this 84kHz bode plot .CSV file. This forum do not accept .csv... shame. 
So if you look it as txt use example notepad++ or just download and remove .txt and open it with software what understand very common  .CSV (comma separated variables) format text  (example LibreOffice calc, OpenOffice calc, Exel or what ever)


Next 14 images (bit boring images. Bit more xplanation for this image set is coming as soon as I have again time
But main idea is (it was tiny part of my test series before I make this preliminary Picture 2.)
In these images A to P  generator output is constant +10dBm  and then there is attenuator between Gen out and scope channel 4 (FFT and BP) (50ohm system).
In BodePlots reference/DUTin (Ch3 selected for this) is constant 10dBm.) 
I forget change BP amplitude scale for dBm but in this case dB scale is same, just think there is also m)
When dB scale show 10dB in mean it measure 10dBm level. (I have set system for measure DUT out level ("Mode Vout") instead of DUTout/DUTin ("Mode Vout/Vin")
After BP with 110dB attenuation 10dB signal I shut BP of and look how FFT see this signal (BP was randomly stopped just with this frequency)  As can see it do not have any difficulties to show this -100dBm signal, with more YT trace average it can go more down of course. (FFT is also lot of improved in this FW 6.1.33 version)
Set begin with 0 attenuation. So there is 10dBm signal. List on and List off. Then every 10dB steps to 110dB attenuation.



Atten 0, level 10dBm, BP List on


Atten 0, level 10dBm


Atten 10dB, level 0dBm


Atten 20dB, level -10dBm


Atten 30dB, level -20dBm


Atten 40dB, level -30dBm


Atten 50dB, level -40dBm


Atten 60dB, level -50dBm


Atten 70dB, level -60dBm


Atten 80dB, level -70dBm


Atten 90dB, level -80dBm


Atten 100dB, level -90dBm


Atten 110dB, level -100dBm


FFT, Same situation as in previous last image. Atten 110dB, Ch4 level -100dBm

Last attachment is one data "list" CSV about 10dBm level BB sweep, (remove .txt)

[rf-loop]

Reserved for continue (because  images, attachments limit in one msg)

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Reserved fo continue

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Reserved for future

[rf-loop]

Some corrections and eta (Reply #2)



Updated:
(Reply #3)
preliminary level range ("dynamic range")

Added 84kHz XTAL resonator BP
Added full resolution saved data table partial picture (also downloadable full table as .CSV)

Added just one tiny sample set of images, just for example, about testing level range/dynamic.

I have now some lack of time make furher tests etc. (later more)

If you comment in this thread, please only things about BodePlot II.  There is lot of other topicks for other things with this scope! So we can avoid situation wheree no one can find anything if all is mixed mess. And if not, make new.

[rf-loop]

Here is "fun" comparison.

SSA image is from 3 years old example for show some SSA3000X features, not specially made for testing filter. (not perfect test setup)
SSA TG - Filter - SSA IN
Span 60kHz

Same with SDS1000X-E  BodePLot II
SDG1000X - Filter - SDS1x04X-E BP II
Same 60kHz span.  Roughly same kind of test setup (not perfect setup as also situation what was with SSA)

Note bit different vertical scale. SSA scale is 8dB/div and SDS scale is 10dB/dif also test signal level different.

Only big difference is sweep time. (note that also SSA was bit slow due to settings)
Of course BodePlot II is more slow due to very different process. Scope do freq steps and after every step it control channel gain (necessary due to 8bit ADC) and do frequency selective level measurement and here is maximal 500 measuring points in use.  SSA working principle is different.
BPII is over 20 times slower (with these settings) if set BPII bit differently it can be much faster and still image do not have big difference. In this image resolution is maximal and also channel gain in auto mode.

But as can see Siglent BodePlot II is more than just salesmans checkbox feature in shining advertisement brochure.. "Scrap a toys and buy real tool."

Also this stop band level is not at all limited by BodePlot, it is limited by DUT and setup (where external cross talk over filter (no shielding between in and out etc).


Siglent SSA3000X


SDS1x04X-E BodePLot II
Channel Gain Auto.






Next image is example what happen when Channel Gain Auto is OFF (Channel Gain Hold mode)
Now BP II sweeps much more fast. But as can see roughly around -48dB from ADC full range it fall in noise.
If you are working with more than bit over 45dB dynamic range you need use C G Auto mode.
Note that filter highest peak is adjusted using oscilloscope and SDG so that it is just bit under 8div peak to peak in oscilloscope YT display. (there is around 2 div more but normally we use scope YT based  to max display not max ADC.

If you are working with some simple filters or other DUT what do not need over 45-48dB measurement dynamic you can use also C G Hold mode if you carefully first set suitable DUTout channel V/div what do not lead to signal clip in highest level in BodePlot sweep range what is intention to do.



BodePlot II, Channel Gain Auto OFF (Channel Gain Hold mode selected)
Limited dynamic range.
For this I have first used normal oscilloscope mode with this test setup and using SDG to find filter highest and adjusted channel for 56mV/div. (important is that it is below ADC clip level) It give just 8div p-p sine in filter highest point. After then turned BodePlot II on and selected Channel Gain Hold mode so it do not touch this channel sensitivity during sweep.


So if you need more dynamic range keep Channel Gain Auto (it is also default)

If do not need higher dynamic and if need more fast sweep you can turn Channel Gain to Hold mode.
You need set suitable channel V/div your self in oscilloscope mode before open BodePlot II
Important: If you use Channel Gain Hold mode. You need take care that signals do not clip (ADC maximum is 10.2div p-p) but due to better linearity please keep all scope input signals maximum level 8div peak to peak during whole frequency range in use.

[Performa01]

Frequency range 1 – 120MHz with wideband amplifier.

This test should reveal the dynamic range over the full bandwidth of 120MHz that can be achieved when feeding the DUT with an amplified signal. The DUT is a combination of Inline and step attenuators in this example:


Setup

As can be seen from the block diagram, channel 2 of the DSO has been used. I don’t think there’s a significant difference with regard to crosstalk effects, but we get the advantage of near perfect phase accuracy when both reference and output channel belong to the same ADC.

EDIT: Forgot to metion that 50 ohm through terminators have been attached to Channels 1 and 2 of the SDS1104X-E. Channels 3 and 4 have been left unterminated.

The maximum output from the Marconi TF2175 is about +25dBm. The generator level has been set to -3dB, which results in an amplifier output of +24dBm. This is only 4.5dB more than what could be achieved with the SDG6052X alone (at the max. Bode Plot II setting of +19.5dBm). Consequently, this is not even enough to compensate for the signal loss caused by the splitter, hence we cannot expect a significant increase in dynamic range. Nevertheless, this test should be interesting …

Note that the Step attenuator has a constant insertion loss of 1dB.

First a reference measurement without amplifier and DUT, i.e. just the splitter alone, to make sure that there are no unexpected errors in the measurements:


SDS1104X-E_FRA_Ref_Ch2

We can see that the difference between channels 1 and 2 are negligible, so we get an excellent amplitude accuracy within +/-0.1dB for the entire frequency range from 10Hz up to 120MHz.

Now a reference measurement with the DUT and 0dB attenuation (+1dB insertion loss), which shows the frequency response of the TF2175 in the range from 1MHz to 120MHz:


SDS1104X-E_FRA_TF2175+5080.1_0dB_Ch2

Note that we now see the gain of the amplifier (27dB) minus the insertion loss of the step attenuator. The result should be +26dB, but a small deviation can be expected, because the amplifier gain is not 100% accurate of course.

The output level is almost spot-on, the TF2175 frequency response isn’t perfectly flat, yet easily within +/-0.5dB from 1.5MHz up to 120MHz.

Up to 40dB attenuation, there is no major change in the frequency response:


SDS1104X-E_FRA_TF2175+5080.1_40dB_Ch2

At 60dB attenuation, the level is a bit higher than expected, but considering the attenuator tolerances, which are no metrological devices after all, the result is still amazingly close to the expected level.


SDS1104X-E_FRA_TF2175+5080.1_30+30dB_Ch2

At 80dB, the bode plot isn’t very smooth anymore, but still pretty accurate:


SDS1104X-E_FRA_TF2175+5080.1_30+50dB_Ch2

At 90dB noise becomes an issue, level accuracy finally starts to suffer and the total error reaches +0.8dB, where an unknown part of that has to be attributed to the attenuators and the test setup:


SDS1104X-E_FRA_TF2175+5080.1_50+40dB_Ch2

At 100dB I’ve switched the vertical scale from 1dB/div to 5dB/div. We can see that accuracy is still not too bad, particularly in the range 2MHz to 60MHz. With these settings, the noise of the unterminated channels 3 and 4 is clearly showing as it’s rising with frequency:


SDS1104X-E_FRA_TF2175+5080.1_50+50dB_Ch2

Even at 110dB things don’t look too bad up to some 20MHz. If we can tolerate +/-5dB error, this could still be used up to 40MHz. Above that frequency, the signal starts touching the noise floor:


SDS1104X-E_FRA_TF2175+5080.1_50+60dB_Ch2

Finally we take a look at 120dB, where the result could still be of some use up to at least 2MHz:


SDS1104X-E_FRA_TF2175+5080.1_50+70dB_Ch2

As we can see, the usable dynamic range with +18dBm input level to the DUT can be as much as 120dB below a couple of MHz, but is limited to 100dB if we want to utilize the full frequency range up to 120MHz.

Level accuracy has been excellent down to -60dB and was still very acceptable down to -100dB over the full frequency range. We should keep in mind that we usually need best accuracy when characterizing the passband, where the level is high anyway.

Signal level measurements in the stopband usually need not be that accurate and a couple of dB plus or minus doesn’t really matter – all the more so as component tolerances and test setup can have a much higher influence on the results. At levels that low, double shielded cables and high quality connectors should be used throughout in order to get meaningful results.

120dB dynamic means quite a lot. It is the difference between 1V and 1µV, and also 1W and 1pW. Look at the specification of your cables and make sure that the screening efficiency is sufficiently high (I have used cables specified to >105dB up to 2GHz) and keep input and output cables well separated –particularly don’t run them in parallel at close distance.

[rf-loop]

Signal level measurements in the stopband usually need not be that accurate and a couple of dB plus or minus doesn’t really matter – all the more so as component tolerances and test setup can have a much higher influence on the results. At levels that low, double shielded cables and high quality connectors should be used throughout in order to get meaningful results.

Yes - but then also no. It is true that usually stop band level accuracy is not so important but stop band itself can be  very important or even more important - often overlooked or underestimated. Why we do band pass filters, example IF filters for receivers. Because we want block all but pass band signals and there this is simple - more is better. Filter stop band performance is very important when we talk example good analog HF radio. High end and state of art class analog radio can do only if IF filters stop band is excellent with good filter shape. In some most bottom level radios like example just home radios they can be nearly what ever. But in state of art receivers IF filters stop band performance is critical. How ever nice and excellent and perfect and expensive things there is but if IF filters stop bands are crap it is end of game.

Now we have under 1000 euro entry level oscilloscope SFRA system (BodePlot II) what can do lot of for measure also these things - but still not down to excellent IF filters stop band, not even close if we use "normal" test signal levels (without extra tools and even then - bit difficult). Not at all up to state of art class, not even high end class, not even real professional class (shift right price tag decimal point some steps) but still it leave competitors far behind.

Using more low test signal levels still we knock our nose to noise wall very fast.  We are still working with ~<7bit (oh yes digital data bus width is 8bit) ADC oscilloscope in 500 price  group.  And when thinking this, its  BodePlot II performance is amazing in this and also in bit upper price group.



Here is one image what give some tip how this frequency selective sweep works and how it adjust selectivity depending frequency. It also may give partial explanation about this noise floor levels (and dynamic range changes)

During this BP sweep there is fixed frequency generator what generate lot of harmonics (square wave) to DUTout channel (in this case I have made Ch1 as DUTout channel and Ch4 is ref/DUTin.
Most left narrow peak is 230kHz fundamental.

As can see BPII frequency sweeping selective level detector ("sweeping selective level meter") change its RBW filter width depending frequency when it sweep. (if want more deep inspection it need sweep using many separate frequency bands for get enough freq resolution)
As can see there with fundamental freq, ~230kHz BW is narrow (scale is linear), then it step bit more wide, again bit more, then more and finally after ~3.5MHz*) it have ~300kHz width. If go higher frequencies then width again change. (stepping filter width somehow proportionally with sweep freq).

*) Note reply #3 picture 2  change after 3MHz.

[Performa01]

Inter-Channel Crosstalk up to 120MHz.

I’ve stated before that I don’t think that crosstalk would be significantly different for the various channels. Now I’ve actually tested this and the screenshot below shows the crosstalk between channel 1 and all other channels:


SDS1104X-E_Bode_Crosstalk_+18dBm_Ch1

The reference signal is +18dBm, swept from 1kHz to 120MHz. Channel 1 was fed through a high quality double shielded low loss cable with >105dB screening efficiency up to 2GHz and a HP10100C through terminator (50 ohms). All other channels were terminated by the usual 50 ohms BNC end terminators.

As we can see, there is not much difference indeed, except for the frequency range 60kHz – 900kHz, where channels 3 and 4 are actually significantly better.

We can conclude that for passive structures, the dynamic range is limited by the crosstalk effects as listed below:

-   9.5MHz: 110dB
-   55MHz:  100dB
-   100MHz:  90dB
-   120MHz:  87dB

We can see that there is actually a significant benefit in using an external amplifier for boosting the signal into a passive DUT. In a previous posting I have demonstrated how the combination of +27dB amplifier and step attenuator could provide some 100dB usable dynamic range up to 120MHz. This hints on an overall improvement of at least 10dB.

EDIT: Corrected the reference level from +13dBm to +18dBm.

[rf-loop]

Ch-Ch cross talk depends also what channels are in use. 
Also base noise level depends (some amount) frequency due to selective level measurement bandwidth what is stepping more wide when frequency rise. But still effect is marginal. One BW change is roughly around 3.5MHz and this can see if carefully look. We can perhaps see many steps if there is trace average function but there is not.


Here is some individual examples pick-up from previously made quite big set of tests.

There is 4 equal test pairs  so that CH1 is DUTin and CH2, 3 and 4  DUT out.  There is no DUT. These channels are terminated and sensitivity 500uV/div.
Top image DUTin get quite constant level  from start to stop freq. Level is 17.9dBm
Bottom image all same but DUTin signal attenuated 20dB using external accurate HP step attenuator.
Test generator is SDG1062X.  All cables M17/84 with Suhner's of course. Signal from generator to DUTin channel terminated using Tektronix 011-0049-01 feed thru.

Next image CH2 is DUTin, then CH3 and last CH4 and other channels as DUT out.

I have used Amplitude measurement/display mode Vout (instead of default Vout/Vin) so display scale is also dBm  not dB vs DUTin.
Channel Gain is in Hold mode (instead of Auto)
(this setup is ok for this purpose)

In images can clearly see that different channels have different cross talk.
Around 0dBm DUTin cross talk start mostly fall in to noise.

As can see CH1 is quite good for DUTin channel and it is also BodePlot II default DUTin.
(note, channel cross talk may be different in individual scopes)

If think example typical IF filters around 100kHz or around 450kHz or 1.4MHz  it is good to take into account. Depending of course test setups. Typical filter input level is not so high so  there is not so much dynamic range available due to level of noise floor. But still example if max input level is 0dBm there is still over 80dB range with quite good level accuracy and over 90dB with reduced accuracy.  When DUTin signal level is 0dBm or less it do not rise other channels floor or effect is insignificant. If input level need be more low it is all away from dynamic range, noise floor do not change.

Not bad at all.


Note display scale. It is NOT dB vs DUTin signal. It is abs level in dBm!

[KungFuJosh]

I setup a bode plot using an SDG2042X and the SDS1104X-E. The DUT is a supercardioid microphone. I'm assuming I set this up wrong...just because. The test has been running for over 12 hours and is still going.

The settings are in the screenshots. Control is via network. I'm using a 50ohm terminated coax between the SDG and SDS on ch1. DUT is connected with a 10x Pico TA131 probe unterminated on ch3.

Side note: the frequency response for the mic is supposed to range between 40Hz to 16kHz.

[Rerouter]

Sound correct to me, It never stops, it just sweeps across the range endlessly until you stop it. that way you can use it to adjust circuit parameters and see the result

[OwO]

It should be possible to increase dynamic range by adding a variable gain amplifier before the inputs right? You could pre-characterize the VGA at all gain steps and all frequency points during zeroing, and then during measurement it could auto-range at each frequency point.

[Rerouter]

I was corrected earlier on another thread that it does uses the fine channel gain to extract the most vertical resolution it can from each frequency,

The full VGA gain and offset table is stored on the device, even the steps that do not end up being used, so they may be using them, but that would only net you a marginal improvement. I'm not yet clear on if ERES can be used in combination,

[KungFuJosh]

After screwing around more, I mean experimenting, I realized my amplitude was too high for the DUT (first screenshot). The rest of the screenshoots are me "experimenting" more. At least they look cool, right?

How can I reconcile the 50R terminated load on CH1 with a HiZ load on CH3?

For the bode plot to be accurate, do the waveforms need to match well? I tried offsetting the phase, which was about 120 degrees off, but that was never perfect, and the amplitude never matched. The closest was setting the amplitude to 90mVpp.

Thanks,
Josh

[Performa01]

It should be possible to increase dynamic range by adding a variable gain amplifier before the inputs right? You could pre-characterize the VGA at all gain steps and all frequency points during zeroing, and then during measurement it could auto-range at each frequency point.

As explained in the opening posting, the Siglent Bode Plot offers the AGC feature already. Do you really think that 100 to 120dB dynamic range is not enough?

I'm not yet clear on if ERES can be used in combination,

No. The Bode Plot forces the Acquisition mode to "Normal" - and thankfully so, because the DFT filtering in the Bode Plot detector is far superior to the Eres lowpass filter, which might limit the upper bandwidth in an undesirable way.

How can I reconcile the 50R terminated load on CH1 with a HiZ load on CH3?

This is an oversight in the Bode Plot module. The next version will allow to specify separate load impedances for the reference and output channels.

Always specify the output impedance. In your setup it would be high-Z (as it is represented by the x10 probe) and for frequencies that low you could even connect the reference channel without a 50 ohms inline termination. The result will be correct as long as the reference channel sees the same amplitude as the DUT input.

For the bode plot to be accurate, do the waveforms need to match well? I tried offsetting the phase, which was about 120 degrees off, but that was never perfect, and the amplitude never matched. The closest was setting the amplitude to 90mVpp.

It normally should be just a single signal, fed into both the reference channel of the scope and the DUT input. For frequencies above some 10MHz, proper 50 ohms termination and a resistive power splitter is highly recommended.

You can also use the dual channels of the signal generator instead, but then it has to operate in Channel Coupled mode for amplitude, frequency and phase.

For higher frequencies, matched cable lengths are important to minimize the phase error.

[KungFuJosh]

How can I reconcile the 50R terminated load on CH1 with a HiZ load on CH3?

This is an oversight in the Bode Plot module. The next version will allow to specify separate load impedances for the reference and output channels.

Always specify the output impedance. In your setup it would be high-Z (as it is represented by the x10 probe) and for frequencies that low you could even connect the reference channel without a 50 ohms inline termination. The result will be correct as long as the reference channel sees the same amplitude as the DUT input.

Considering this oversight, it doesn't seem functional at all in my current setup.

For the bode plot to be accurate, do the waveforms need to match well? I tried offsetting the phase, which was about 120 degrees off, but that was never perfect, and the amplitude never matched. The closest was setting the amplitude to 90mVpp.

It normally should be just a single signal, fed into both the reference channel of the scope and the DUT input. For frequencies above some 10MHz, proper 50 ohms termination and a resistive power splitter is highly recommended.

You can also use the dual channels of the signal generator instead, but then it has to operate in Channel Coupled mode for amplitude, frequency and phase.

For higher frequencies, matched cable lengths are important to minimize the phase error.

I'm reading that as "yes, they should match." I'm using both outputs from the AWG as described earlier in this thread. One is direct to the scope CH1 with a 50ohm adapter, and the other output goes to my DUT, which then goes through a 10x probe to CH3 on the scope.

With AWG CH2 locked to CH1, it doesn't appear that there's a way for me to have the waveforms match phase and amplitude on the scope.

Am I wasting my time with this? Is there any real benefit to the Bode Plot for audio equipment (specifically microphones and tube amplifiers)?

Thanks,
Josh

[Electro Fan]

Hi rf-loop,

This is kind of off topic, but first thanks for all of your many contributions to the forum.  Your explanations are very helpful and your documentation is very impressive.  Any chance you can share what editing program you use to annotate screen shots? 

Thanks!

[Performa01]

How can I reconcile the 50R terminated load on CH1 with a HiZ load on CH3?

This is an oversight in the Bode Plot module. The next version will allow to specify separate load impedances for the reference and output channels.

Always specify the output impedance. In your setup it would be high-Z (as it is represented by the x10 probe) and for frequencies that low you could even connect the reference channel without a 50 ohms inline termination. The result will be correct as long as the reference channel sees the same amplitude as the DUT input.

Considering this oversight, it doesn't seem functional at all in my current setup.

Quite obviously, the load impedance is irrelevant for voltage/current measurements, so this is only applicable when dBm units for power measurement (mainly in RF applications) are used.
For professional audio, dBu is standard, but Vrms, dBV or even arbitrary dB might be just as useful, depending on the actual task.

This means, you will of course not see any difference as long as you don’t select dBm units for the measurement. It is also not a problem if you just look at the DUT output (Pout) – you just need to specify the load impedance to get a correct power measurement.

To cut a long story short, there is only a problem when measuring the power gain, i.e. Pout/Pin and the load impedance of input and output are not the same. This could yield a maximum error of 3dB. As stated before, this is a known issue and will be fixed at some point.

For the bode plot to be accurate, do the waveforms need to match well? I tried offsetting the phase, which was about 120 degrees off, but that was never perfect, and the amplitude never matched. The closest was setting the amplitude to 90mVpp.

It normally should be just a single signal, fed into both the reference channel of the scope and the DUT input. For frequencies above some 10MHz, proper 50 ohms termination and a resistive power splitter is highly recommended.

You can also use the dual channels of the signal generator instead, but then it has to operate in Channel Coupled mode for amplitude, frequency and phase.

For higher frequencies, matched cable lengths are important to minimize the phase error.

I'm reading that as "yes, they should match." I'm using both outputs from the AWG as described earlier in this thread. One is direct to the scope CH1 with a 50ohm adapter, and the other output goes to my DUT, which then goes through a 10x probe to CH3 on the scope.

With AWG CH2 locked to CH1, it doesn't appear that there's a way for me to have the waveforms match phase and amplitude on the scope.

Sorry, but I don’t quite understand your problem? Are you saying you can’t get a perfect channel tracking for amplitude, frequency and phase on your AWG?

Am I wasting my time with this? Is there any real benefit to the Bode Plot for audio equipment (specifically microphones and tube amplifiers)?
 

Bode Plot is perfectly suitable for audio applications – it is just a matter of the frequency range.

Here is an example for a simple ~20kHz RC lowpass filter:


SDS1104X-E_FRA_CTC_100nF_Mylar

Here’s another example; this is a discrete transistor amplifier with 60dB gain (measurements shows less because for this test there is also a ~14dB attenuator at the amplifier input). This is with the SDS5000X, but the Bode Plot application has the same core as on the SDS1004X-E:


SDS5104X_FRA_R41_-A14+G60dB_Ch2

So this is perfectly suitable to analyze and document the frequency/phase response of a tube amplifier.

Your question about the microphone is a different story. Measuring the frequency response of a microphone is about the most demanding task of all and at least as much of a challenge as antenna measurements in telecommunications.

The Bode Plot of the SDS1004X-E is not ideal for such tasks, because it cannot apply a correction curve, hence cannot be calibrated. The requirements for the test setup are a true challenge and very expensive on top of that.

The DUT would then usually look like this:


Mic_FRA

Since a microphone is a transducer that has no electrical input, we need another transducer to convert the electrical signal to sound pressure (some sort of reference loudspeaker). The latter will certainly not have a flat response, so you need to know its detailed frequency/phase response in order to apply the required correction to the measurement results. Such a calibrated sound pressure source together with the anechoic chamber would be prohibitively expensive for a hobbyist I think.

[rf-loop]

In some special cases perhaps also this kind of principle is possible?  (as my nickname tell I'm more RF.... )
(of course it need well known ref Mic etc...  and very carefully istalled so it do not mess Microphone under test and it get as perfectly same as Mic under test get.)

[Performa01]

In some special cases perhaps also this kind of principle is possible?  (as my nickname tell I'm more RF.... )
(of course it need well known ref Mic etc...  and very carefully istalled so it do not mess Microphone under test and it get as perfectly same as Mic under test get.)

Thanks for pointing this out. It is of course viable, but now requires an calibrated measuring microphone, which makes the setup even more expensive. Just like reference sound pressure sources, measuring microphones do not have a perfectly flat response, but are calibrated, i.e. their response is precisely known and the corresponding correction can be applied to the measurement results.

EDIT: I think your point is that the sound pressure source needs not be calibrated, but it still needs to be high quality to come close to a point shaped source without partial oscillation of the membrane to give a uniform sound field.

[KungFuJosh]

In some special cases perhaps also this kind of principle is possible?  (as my nickname tell I'm more RF.... )
(of course it need well known ref Mic etc...  and very carefully istalled so it do not mess Microphone under test and it get as perfectly same as Mic under test get.)

Thanks for pointing this out. It is of course viable, but now requires an calibrated measuring microphone, which makes the setup even more expensive. Just like reference sound pressure sources, measuring microphones do not have a perfectly flat response, but are calibrated, i.e. their response is precisely known and the corresponding correction can be applied to the measurement results.

EDIT: I think your point is that the sound pressure source needs not be calibrated, but it still needs to be high quality to come close to a point shaped source without partial oscillation of the membrane to give a uniform sound field.

Very interesting. It appears that you're suggesting that the test should use a live capsule on the microphone. I often test the mic prior to installing a capsule. So the mic would have a ~72pF dummy load instead of the capsule, and then I insert a signal directly to the mic circuit.

Shouldn't this be significantly simpler to test the circuit that way?

Thanks,
Josh

[rf-loop]

In some special cases perhaps also this kind of principle is possible?  (as my nickname tell I'm more RF.... )
(of course it need well known ref Mic etc...  and very carefully istalled so it do not mess Microphone under test and it get as perfectly same as Mic under test get.)

Thanks for pointing this out. It is of course viable, but now requires an calibrated measuring microphone, which makes the setup even more expensive. Just like reference sound pressure sources, measuring microphones do not have a perfectly flat response, but are calibrated, i.e. their response is precisely known and the corresponding correction can be applied to the measurement results.

EDIT: I think your point is that the sound pressure source needs not be calibrated, but it still needs to be high quality to come close to a point shaped source without partial oscillation of the membrane to give a uniform sound field.

Very interesting. It appears that you're suggesting that the test should use a live capsule on the microphone. I often test the mic prior to installing a capsule. So the mic would have a ~72pF dummy load instead of the capsule, and then I insert a signal directly to the mic circuit.

Shouldn't this be significantly simpler to test the circuit that way?

Thanks,
Josh

First your question about my images editing.
Because these are technical pictures, example instrument display copy (never use jpg, jpg is for photographs)  and need simple things - like txt, some highlights or color balance etc and of course it have quite nice advanced batch conversion/adjust tools. Fast and easy but still can do many things and it is not mammoth like some photographers Photoshop or GIMP etc.
I have used over 20 years Irfan Skiljan's nice Irfanview.  For this kind of simple technical images purposes it have today lot of tools. It is today, and have been long long time,  lot of more than just viewer what is was over 20 years ago when IrfanView was launched.. So this name is bit fun today, but name have history. In beginning it wast just more like simple viewer, at this time world was bit different.

It is not suitable for real The Photographs editing. Camera Photographs are other things.
(today with Irfan you still can do really meany things.. (Irfan + plugins package))



But then return to the actual subject.

So you are testing microphone without microphone.
I think this do not belong to this thread at all. It belongs under topic something like "how to measure microphone frequency response"

If you are testing microphone amplifier circuit freq. response alone - then you need tell you are testing this kind of electronic circuit (explanation).  Microphone is receiving acoustic waves in air. (because you talk this kind of microphone. Of course, the medium in which mechanical vibrations are transmitted can be something other than air.) Normally when we talk microphone (music, speak etc sounds) frequency response we talk this frequency response how it move acoustic waves in air to electric signal. Other question is after then how these electronic circuits handle this microphone "capsule" signal. These circuists are not "microphone". and if you talk alone these amplifier / buffer circuits response you do not talk microphone frequency response. So these kind of things very easy mess whole discussion and soon, as also here now, we are like out from BodePlot II things.

Microphone real freq response measurement is imho really different case. It need sound. For other than crap result it is quite complex case and need - hard knowledge how to do it and also instruments for do it. There also BodePlot II can use.

If you  want only test this microphone amplifier without microphone itself (capsule) you can of course do it also using BodePlot II. But now it looks your problem is not at all BodePlot II things. You need perhaps help how to do this test setup between your circuit and  SFRA system. Please open new topic for it and give deep detailed information about your this DUT.  Schematics and specifications what ever are available. Perhaps then someone(s) can try help how to do it. Includind also perhaps some tips how to then finally do BP II settings. But first you need some help for do hardware test setup for this.  First you need good setup.  BPII settings are then in final case.
 
For your self learn how to use BPII itself:

I recommend you do some very very simple circuit, just example RC filter.
Then run BPII with it and exercise and try understand all settings what they are and how they affect what you get on display. Also including understanding level scales. Adjusting display when BPII is running
 
Sidenote:(Siglent need improve this vertical autoscale so that user can select it or use last user adjusted vertical and remember it if stop and adjust example horizontal or other parameters. Now it is frustrating to adjust these scales every time again after start sweep because it always goes to autoscale and least I have not find how to deny vertical autoscale for level and phase draw.)

I highly recommend to firtst exercise with known circuits if it is not clear how to use SFRA (BodePlot II). For base level exercise/learn  how to use BPII , imho, it is best to use known circuit what result we already roughly know and simplest circuit is example 1st or 2nd order RC low pass (or something like it, band pass, high pass etc). If you want simplest possible DUT and frequency can be "what ever" because it is only for learning. You can use setup (if you are sure you can set SDG for tracking mode with equal outputs so that CH2 is tracking CH1 with 0 phase, 0 level and 0 freq difference.)

Connect CH1 to scope CH1 (as DUTin) (coaxial, 50ohm termination)

Connect probe 1. BNC end  to SDG CH2 Output BNC.
Connect probe 2. to scope channel (example CH2) as DUTout.
Connect probes GND wires together. Connect probe tips together. Set both probes for 1x.
These probes are now your DUT.  This DUT is low pass filter, corner somewhere well under 10MHz

If you now want look lot of lower freq things.
Just keep this setup but take example 100ohm resistor and 100nF capacitor. Connect capacitor other end to probes GND joint. Open probes tips joint. Connect capacitor other end to probe 2. tip. Connect also resistor other end to this joint.   Then connect resistor other end to probe 1. tip.
Start exercise using BPII default settings and set sweep logarithmic and start from example 1kHz to 10MHz.
Of course you can do some other filter or cascaded filters.
Here can find nice tools for calculate these and also get calculated responses. So you can see how close practice and theory goes when you look your BodePlot II results. (of course calculus are made using ideal components what do not exist at  all in real world, never. Even DC voltage exist only in theory books but not in real world. Never.)

But I hope we can see this "microphone what is not microphone" testing things goes to under some other new topic or other appropriate thread.

[KungFuJosh]

I'll try those simple tests and eventually start a new thread if I decide to keep the SDG. This seems to be more hassle than it may be worth.

BTW- That was somebody else that asked about your graphics. My day job is web and graphic design. I'm well versed in the adobe suite, and I have irfanview too.

Thanks,
Josh

[rf-loop]

I'll try those simple tests and eventually start a new thread if I decide to keep the SDG. This seems to be more hassle than it may be worth.

BTW- That was somebody else that asked about your graphics. My day job is web and graphic design. I'm well versed in the adobe suite, and I have irfanview too.

Thanks,
Josh

Sorry, it was @Electro Fan who ask this.

Btw, I do not understand what "hassle" there is. SFRA works just as SFRA works. Even if you buy big brand SFRA machine there is very important to think and understand what things machine do not for you.  User must arrange a suitable test connection setup between DUT and Analyzer. User is responsible about test signals are right and DUT and test instrument see suitable and good quality signals.  Some times it need also thinking, knowledge and experience. First before all, need fully understand how test instrument works and what are all things there. I want easy, immediately all for me just as in movies and stories. It do not work like this.
I have been in situations where need first design test setup. In some cases it need lot of work.  Finally after long long work and design etc... then power up test instrument and push three - five buttons and turn some knobs and after some minutes there is nice result on screen. If someone look when start instrument and how easy all goes to final nice graph on display... then he may think why company pay to you this salary. Just because he did not know what was 99.99% of this work what final and result he simply see, one dirty graph on the screen..

It is because every time you measure something (connect something, probe, wire or what ever) to DUT you change DUT. More or less. Yes in many simple low freq audiuo things this must not care so much except perhaps if go to some state of art things. Some times it is major problem and sometimes it may need deep knowledge and hard design etc to know how to arrange probing and how to know how much it affect DUT and how much it bend result what we hope is as accurate truth as possible.   Never overlook how much need do work for good reliable test setup, its is perhaps most important (and some times frustrating) thing when do some testing.
Turning instrument knobs is most easy peace of this cake. And even in this, doing instrument settings, many even experienced peoples are messing because they do not know how instrument is designed to work. So, also knowledge need include - always: "know your tools and instruments". And this is what need exercise and study and it IS hard work and it need do or if not  then just better stay with toys and playing some simple things. There is no free lounges. Home works need do or if not then some  day all feels "difficult" and messy. Look some videos around internet and you know what I mean...but it is not appropriate to talk about it here.

[tautech]

This ^^^ and so much all this !

Practice with simple pass filters and get to understand BPII. It does take time but this investment in time and X-E plus AWG is much less than other equipment that has similar capability.

[mrprecision]

I have tested the Bode Plot Function of my scope (SDS1104X-E) and have been very enthusiastic about it so far. I connected the scope to the generator (DG2042X) via Ethernet, this worked without any problems right away. However, there seems to be a problem with the Bode Plot function.
In the simple example I tested a passive filter of the 1st order with 100Hz at -3dB. The sweep for the Bode Plot function was chosen from 10Hz to 1kHz with 10 points per decade. "Channel Gain Auto" was selected under the channel settings.
Then the Bode Plot measurement was started. The first run is as expected. However, the first point in the Bode Plot is incorrectly determined in all further runs. In my view, this is a mistake. However, if you select "Channel Gain Hold" under the channel settings, this incorrect measurement does not occur. It also appears to occur only at low start frequencies.

Video
http://www.schaeck.eu/download/eev/siglent_bode_2_error.mp4

[Pitrsek]

Any clue as to why is the low limit set to 10Hz?

[tautech]

Any clue as to why is the low limit set to 10Hz?

Offer a valid use case for under 10 Hz and we'll send this request to Siglent.

[n3mmr]

Any clue as to why is the low limit set to 10Hz?

Offer a valid use case for under 10 Hz and we'll send this request to Siglent.

For really-high-quality audio power amplifiers, a bode plot of the range 0.1 Hz to, say, 100 Hz will enable a designer to accurately predict the audibility of artefacts coming from attempts to limit the vlf range by steep slope high pass filtering of subsonics.

[mrprecision]

I have tested the Bode Plot Function of my scope (SDS1104X-E) and have been very enthusiastic about it so far. I connected the scope to the generator (DG2042X) via Ethernet, this worked without any problems right away. However, there seems to be a problem with the Bode Plot function.
In the simple example I tested a passive filter of the 1st order with 100Hz at -3dB. The sweep for the Bode Plot function was chosen from 10Hz to 1kHz with 10 points per decade. "Channel Gain Auto" was selected under the channel settings.
Then the Bode Plot measurement was started. The first run is as expected. However, the first point in the Bode Plot is incorrectly determined in all further runs. In my view, this is a mistake. However, if you select "Channel Gain Hold" under the channel settings, this incorrect measurement does not occur. It also appears to occur only at low start frequencies.

Video
http://www.schaeck.eu/download/eev/siglent_bode_2_error.mp4

Back to my Question: But why is the already existing function only working for the first run?

[Performa01]

I have tested the Bode Plot Function of my scope (SDS1104X-E) and have been very enthusiastic about it so far. I connected the scope to the generator (DG2042X) via Ethernet, this worked without any problems right away. However, there seems to be a problem with the Bode Plot function.
In the simple example I tested a passive filter of the 1st order with 100Hz at -3dB. The sweep for the Bode Plot function was chosen from 10Hz to 1kHz with 10 points per decade. "Channel Gain Auto" was selected under the channel settings.
Then the Bode Plot measurement was started. The first run is as expected. However, the first point in the Bode Plot is incorrectly determined in all further runs. In my view, this is a mistake. However, if you select "Channel Gain Hold" under the channel settings, this incorrect measurement does not occur. It also appears to occur only at low start frequencies.

Video
http://www.schaeck.eu/download/eev/siglent_bode_2_error.mp4

Back to my Question: But why is the already existing function only working for the first run?

Yes, there's a timing problem whenever the vertical gain of the measurement channel exceeds 1V/div.

There is a base range up to 100mV/div that doesn't require an input attenuator.
For the vertical gain settings up to 1V/div the first 20dB attenuator is activated.
For the vertical gain settings up to 10V/div the scond 20dB attenuator is activated on top of that.

These attenuators are relay operated and quite obviously the 2nd attenuator causes additional time delays that are not allowed for in the Bode plot firmware.

Knowing this, the workaround is simple. Just lower the stimulus level by 3dB, so that the vertical gain of the measurement channel (Ch.2) never exceeds 1V/div. With this setting you can have glitch-free measurements over more than 100dB dynamic range (the first attenuator doesn't pose a problem):


SDS1104X-E_Bode_LP100Hz_10-10MHz+3dBV

In the screenshot above, the 100Hz lowpass filter is measured up to 10MHz. As can be seen, my filter works as expected up to some 2MHz, then there is a resonance with a maximum attenuation of about 100dB and after that, the attenuation is decreasing again. The phase plot also clearly documents this.

Numerous passes have been made and the data at 10Hz have always been correct. Of course I've also tried lower spans, including the setting that you've used (10Hz to 1kHz). It all works fine.

[Performa01]

Any clue as to why is the low limit set to 10Hz?

The Bode Plotter uses AC coupled input channels, which simplifies operation significantly. Even though the corner frequency is below 3Hz, the phase shift is significant even above that frequency and slight differences between channels (component tolerances) cause additional phase errors in the measurement channels with regard to the reference channel. This is the reason why 10Hz has been chosen.

In DC coupled mode, any DC offset can easily ruin the dynamic range. The DC offset might be too high to be compensated by the internal offset DAC, and even if it is within range, this would cause additional effort.

Knowing all this, I've still requested a lower frequency limit of at least 0.1Hz a long time ago, but it seems that Siglent doesn't see much benefit in spending the effort to implement this, since the practical use cases are limited indeed.

One Argument is that the Bode Plot (that is not fast anyway) would get painfully slow at frequencies that low: at 100mHz, a single measurement takes at least 10 seconds, filtering/averaging not even factored in. This means, if Siglent ever implements that, you need to be aware that this option is for tests running over night only

[mrprecision]

These attenuators are relay operated and quite obviously the 2nd attenuator causes additional time delays that are not allowed for in the Bode plot firmware

I understand the problem with the 2nd attenuator, you think that could be fixed by Siglent. Why are no additional time delays are allowed for the bode plot firmware?

[rf-loop]

These attenuators are relay operated and quite obviously the 2nd attenuator causes additional time delays that are not allowed for in the Bode plot firmware

I understand the problem with the 2nd attenuator, you think that could be fixed by Siglent. Why are no additional time delays are allowed for the bode plot firmware?

I belive there is wrong word (allowed). Perhaps it is something like "additional time delays are not been adquately addressed"  Lets hope some future FW fix this.

[rf-loop]

One Argument is that the Bode Plot (that is not fast anyway) would get painfully slow at frequencies that low: at 100mHz, a single measurement takes at least 10 seconds, filtering/averaging not even factored in. This means, if Siglent ever implements that, you need to be aware that this option is for tests running over night only

^ This.

@mrprecision
SDS BodePlot works using frequency selective "receiver" principle (receiver center freq sweeps together with generator sweep, bit like SA with tracking generator. Even more, BP also adjust RBW during sweep related to current freq. It adjust receiver center during sweep and also it adjust Resolution Band Width automatically proportional to frequency) and naturally this part is very slow when go to very low frequencies specially with sub Hz selectivity because...
Try play under 10Hz and down to under 1Hz with good resolution using FFT...  we just meet limits of this kind of systems. 0.5kEur oscilloscope can not be everything. Still its SFRA performance is far over any others in this <1kEur price group (scope + generator) and even in bit higher class. With these limits we need live.
And of course hope they find solution for this attenuator delay time better or what ever is this reason. It have been quite long time this problem has been found.

[mrprecision]

It seems to be a timing problem with the 2nd attenuator.

Secound run with 6Vpp:


Secound run with 0.5Vpp

[Pitrsek]

The phase difference between channels should be taken care off during calibration, that's not a reason at all. Drop in the injection voltage could be compensated on the generator side.
Actually I believe that they really should include a DC coupling mode, especially if this thing is coming to scopes with 50R inputs(most of the scopes that I worked with had 50R input DC coupled).
And with 50R inputs, there is full new world of S parameters and impedance measurements... 
Yes, measuring low frequency takes time, that's give fact. I'm not asking for making it a default settings, I'm asking for a possibility to go lower, if the user wants to. 
Use case is rather simple, try measure open loop gain of an opamp... For a lot of slower opamps, the dominant pole is rather low.

[Performa01]

The phase difference between channels should be taken care off during calibration, that's not a reason at all. Drop in the injection voltage could be compensated on the generator side.

Calibration in a DSO takes care of the runtime differences between channels, which in turn lead to a continually increasing phase shift proportional to the input frequency. A DSO cannot compensate for the phase errors caused by slight differences in the corner frequencies of the AC coupled input path.

What you’re describing, sounds much more like the user calibration of a VNA test setup. In contrast, Bode Plotters don’t do a calibration/normalization run.

Actually I believe that they really should include a DC coupling mode, especially if this thing is coming to scopes with 50R inputs(most of the scopes that I worked with had 50R input DC coupled).

Yes indeed, all Siglent DSOs beyond the SDS1000X-E entry level have switchable 50 ohm inputs, starting with the SDS2000X-E. And yes, these inputs are either DC or AC coupled, regardless of the selected input impedance.

And with 50R inputs, there is full new world of S parameters and impedance measurements... 

Once again you are talking about a VNA here – and apart from that I don’t think I have ever seen s-parameters used below 10Hz

Seriously though, you don’t suggest that a cheap DSO should be able to replace a VNA with s-parameter test set, do you? Or – to get back to the <10Hz discussion – a Dynamic Signal Analyzer?

The fact that the Bode Plot in Siglent DSOs is more than just a me-too feature, hence can be used for some serious work in certain areas, cannot hide the fact that it is just a software module in an entry level (or midrange, in case of the SDS5000X) DSO, hence it's got to have some limitations.

Yes, measuring low frequency takes time, that's give fact. I'm not asking for making it a default settings, I'm asking for a possibility to go lower, if the user wants to.

You need not convince me. As stated earlier, I’ve already requested this quite a while ago, because I also know use cases for this, like very slow high precision control loops.

The problem is that Siglent has lots of projects and limited resources, so they need to prioritize things. Extending the range of the Bode Plot certainly isn’t high on their list.

In fact I constantly need to promote and defend the Bode Plotter, especially against consultants coming from the higher end industries, because the Bode Plot is generally seen as a hobbyist feature, or for one man workshops at best. I fight for it, simply because I was once young and on a budget myself and want hobbyists to get something useful for the most common use cases without having to reach out for some half-broken ancient boat anchor.
 
Under these preconditions, I’m glad that we still got the Bode Plot II and I’m positive it will see further improvement - just not as a high priority.

Use case is rather simple, try measure open loop gain of an opamp... For a lot of slower opamps, the dominant pole is rather low.

While this sounds like a use case, I don’t think many will do that.

The characterization of chips in general, like operational amplifiers, is the task of the semiconductor manufacturer (who certainly won’t use an SDS1004X-E for this) and they publish the results in the data sheets. So why not just use that?

The only other scenario I could think of would be the incoming components inspection in the industries using that chip, but once again I cannot imagine them using a cheap DSO for the task. And they will most likely not care for the corner frequency in the open loop response, but just measure the frequency response at the intended gain instead.

In general, measuring the open loop response of an OpAmp is far from being straight forward and consequently not common at all.

[Pitrsek]

We've started to mix two thing together,  let me separate that.
10Hz - I consider the limit to be bit to high, I'm not telling it's useless. I think it could be improved. Open loop gain was an example because that's what I'm doing now. But in general any slow loop would benefit from the expanded bandwidth - sometime the dominant pole is really low. The open loop measurement is actually rather simple and straight forward. If you have inverting configuration, measure voltage at virtual ground (pre-amp is needed) and divide by opamp output voltage. If it's no-ninverting configuration, differential amplifier is needed to extract opamp input voltage.
You'd be surprised how many vendors do not bother to state the details of the open loop gain... I think it's a bit of a chicken and egg problem.  It's not done regularly because you do not have the needed equipment, and it kinda works most of the time(until it does not...). Yes, it's a bit of niche at this time.
It's a same as loop gain measurement - look at the amount of literature and info that's available now. It's not like the theory has changed or that the issues were not there 20yr ago, it's just that tools were not as widespread as are now. Now every scope mfgr now has an appnote about loop gain measurement.
In my previous jobs, before we bought impedance/loop gain analyser, there was not much general interest in impedance profile of discrete parts, or loop measurement. Then we bought analyser, and everybody saw how useful it is. The company bought another one to keep up with demand from engineers... Once you make it accessible, then everyone is like "how could i lived without it"?

I'm not suggesting that you should be able to replace your VNA with a budget scope, I'm suggesting that with some extra effort, the bode plotter could be made much more useful. And most of the required stuff is already there!
Personally I consider impedance profile measurements to be extremely useful - again, some manufacturers do not provide models/data, sometime the bias effect are missing, or you'd like to know output impedance of power supply, or a filter. There are a lot of good reasons why you'd like to do impedance sweeps.  Yes, you have a hard limits in bandwidth and dynamic range and you'll never have the same performance as dedicated equipment, but for quite some measurements it could well be enough. 

Even if it's a software module, i believe it's extremely useful. And if calibration routines are added, so you can make impedance sweeps, it could be pretty awesome. I'm well aware that full calibration routines are not trivial, but it's no rocket science either(especially the normalisation).

TLDR - it's great feature, I'm glad it's there, it could be improved to make it quite a bit more useful.

 

[Pitrsek]

Actually since they do sell VNA, they ought to have a decent grasp about the calibration routine. Probably different team, on different floor, but the know how is there. Just saying, It could be a nice intro in the impedance measurements for users on budget. And it would be useful...
You'd like to have a bigger dynamic range and higher frequency limit? Here, there's our VNA.

And this would conclude my 2cents of unsolicited free advice 

[mrprecision]

I had contact toSiglent, they will fix the bodeplot 2 bug with the next firmware version.

[mrprecision]

I have tried out to measure the impedance vs. frequency. I was surprised how good this worked out. After the first tries I have build a connection box for better results. I have measured than a 1uF Wima capacitor. This turned out very good and I have compared it with the results of a Rode&Schwarz network analyzer. For privat use the results are very good up to 20MHz. If I set the probes correct than the y-axis scaling is also correct in dB. You only have to calculate Z=10^(dBvalue/20) and you get the value in ohms. Someone tried this also out?

See the results:

[khutch004]

Any clue as to why is the low limit set to 10Hz?

Offer a valid use case for under 10 Hz and we'll send this request to Siglent.

For really-high-quality audio power amplifiers, a bode plot of the range 0.1 Hz to, say, 100 Hz will enable a designer to accurately predict the audibility of artefacts coming from attempts to limit the vlf range by steep slope high pass filtering of subsonics.

People building bass guitar amps and high pass filters for them are interested in evaluating the very low frequency response. They often use an HPF to prevent the cone excursions from exceeding safe limits if subsonic information appears at the amplifier inputs. Bass cabs often walk a fine line between being able to generate a high output level at 30 to 60 Hz and blowing up when presented with low frequency noise and often some help from the amp or a filter in front of the amp is needed.

A better question to ask is the 10Hz low limit arbitrary or is it driven some important cost or reliability concern?

If it was just an arbitrary limit then why NOT extend it as far as possible?

People building filters for some scientific applications will want to test at sub 10Hz frequencies. There may not be terribly many such people but again if the limit is arbitrary then it should be removed.

[mrprecision]

I have tried out to measure the impedance vs. frequency. I was surprised how good this worked out. After the first tries I have build a connection box for better results. I have measured than a 1uF Wima capacitor. This turned out very good and I have compared it with the results of a Rode&Schwarz network analyzer. For privat use the results are very good up to 20MHz. If I set the probes correct than the y-axis scaling is also correct in dB. You only have to calculate Z=10^(dBvalue/20) and you get the value in ohms. Someone tried this also out?

Because some users asked me, here are pictures of my connection boy for the impedance measurement with the Bode Plot II function. Has anyone tried to measure the impedance vs. frequency with the Bode Plot II function?

[rf-loop]

Nice work.

---
About new SDS2000X Plus Bode Plot.
SDS2kX+ have 50MHz internal signal generator. Of course with it can not do setups what use SDG with 2 output settings.

I have not SDS2000X Plus and here in China all who knows are now spring holidays.

Who can check if this model can use internal signal generatorfor BP use only without FG license installed. Even with scopes with external SAG USB generator do not need SAG  license if use this only for BodePlot.
If use SDS2kX+ internal signal gen only for BP (BP controls it automatically) do it work without FG licence.

[mrprecision]

About new SDS2000X Plus Bode Plot.
SDS2kX+ have 50MHz internal signal generator. Of course with it can not do setups what use SDG with 2 output settings.

I have not SDS2000X Plus and here in China all who knows are now spring holidays.

Who can check if this model can use internal signal generatorfor BP use only without FG license installed. Even with scopes with external SAG USB generator do not need SAG  license if use this only for BodePlot.
If use SDS2kX+ internal signal gen only for BP (BP controls it automatically) do it work without FG licence.

I use the Scope SDS1104X-E and the generator SDG2122X and I don't need any licence for the BodePlot and FunktionGenerator. I connect them over ethernet.

[rf-loop]

About new SDS2000X Plus Bode Plot.
SDS2kX+ have 50MHz internal signal generator. Of course with it can not do setups what use SDG with 2 output settings.

I have not SDS2000X Plus and here in China all who knows are now spring holidays.

Who can check if this model can use internal signal generatorfor BP use only without FG license installed. Even with scopes with external SAG USB generator do not need SAG  license if use this only for BodePlot.
If use SDS2kX+ internal signal gen only for BP (BP controls it automatically) do it work without FG licence.

I use the Scope SDS1104X-E and the generator SDG2122X and I don't need any licence for the BodePlot and FunktionGenerator. I connect them over ethernet.

Answer is right if I ask this but not answer to my question at all.
Btw, I connect FG always via direct USB. Why... well... because no one is then never delaying communication between Scope and FG. (of course same if run bare point to point LAN)

Of course SDS1104X-E do not need. Have you ever read this thread from beginning, all what I have explained and tested...

Also as we know SDS1kX-E do not have internal FG but SDS2kXPlus have and for this was my question. Is it possible to use its internal generator for Bode without activating this FG using Siglent licence for FG, what also activate manual control for internal FG but if user is not interested for use it other than Bodeplot).

This question is based to fact that SDS1kX-E have optional external FG (you know this SAG) and if buy this option he often byt this SAG hardware and then licence for use it as common FG. In SDS1kX-E case SAG (external box without controls) can use for Bode without purchasing its control license key. In this case it can still use for Bode but nothing else.
 
Now SDS2kXPlus have internal 50MHz FG what can use as common FG if purchase license key so user can run and control it using UI what is built in scope. And some people may like use it only for Bode and not want buy license key because overall this FG is not so advanced. So is it usable for Bode alone without license, this was and is question.

[torquil]

I have a Siglent SDS1104X-E that I use together with an SDG1062X, and the Bode Plot II function is very nice! But there seems to be a limit so that the y-axis cannot go beyond values in [-200,200], which is a bit troubling when using the BPII for impedance measurements with a linear y-scale.

I have made a small connection box for easily connecting everything required for an impedance measurement. One of the items I tested was a 3:1 transformer with a 100R load, so the input impedance will be beyond 200 Ohm. To get the impedance I provide voltage and current measurements to the Bode Plot II system, and use the Vout/Vin display (Vin represents current for this measurement) and a linear display on the y-axis.

These measurements work as expected, but since the input impedance is beyond 200 Ohm for the transformer, the graph disappears outside the plot area. I am forced to either manipulate the probe multiplication factor or use a logarithmic scale. I know I can get the CSV, but it would be nice to have an immediate and correct plot.

Anyone here know if this has been reported? I do use the newest firmware versions.

[mrprecision]

how can you set the bodeplotII to linear yaxis?

[rf-loop]

how can you set the bodeplotII to linear yaxis?

You did not tell what axis, vertical (level) or horizontal (freq)


This image have been in this thread long long time and all other informations. Just read. 

Look top main menu and follow "Display"
There is Axis type (horizontal) select lin / log
For vertical select Scale V instead of dB  and scale units Vpp/Vrms/dBV/dBu/dBm/Arbitrary dB



I am not absolutely sure in all is exactly as shown after some FW update but almost all like this.

[mrprecision]

I have a Siglent SDS1104X-E that I use together with an SDG1062X, and the Bode Plot II function is very nice! But there seems to be a limit so that the y-axis cannot go beyond values in [-200,200], which is a bit troubling when using the BPII for impedance measurements with a linear y-scale.

I have made a small connection box for easily connecting everything required for an impedance measurement. One of the items I tested was a 3:1 transformer with a 100R load, so the input impedance will be beyond 200 Ohm. To get the impedance I provide voltage and current measurements to the Bode Plot II system, and use the Vout/Vin display (Vin represents current for this measurement) and a linear display on the y-axis.

These measurements work as expected, but since the input impedance is beyond 200 Ohm for the transformer, the graph disappears outside the plot area. I am forced to either manipulate the probe multiplication factor or use a logarithmic scale. I know I can get the CSV, but it would be nice to have an immediate and correct plot.

Anyone here know if this has been reported? I do use the newest firmware versions.

I have tried it with my connection box. I found the option to set the y-axis linear. You are right, there are limit of +/-200. That is not very nice. If you activate the table of the values, you can see the correct values. I will report this to Siglent.

How is your connection boy set up? Do you have a photo or a schematic? I have the Scope and an SDG2xxx frequency generator, all Scope probes and the generator is connected to earth. How did you solve this problem?

[mrprecision]

I have send an e-Mail to my Siglent contact regarding the -200/+200 scaling problem. They had also fixed my other bugs I had.

[rf-loop]

I have a Siglent SDS1104X-E that I use together with an SDG1062X, and the Bode Plot II function is very nice! But there seems to be a limit so that the y-axis cannot go beyond values in [-200,200], which is a bit troubling when using the BPII for impedance measurements with a linear y-scale.

I have made a small connection box for easily connecting everything required for an impedance measurement. One of the items I tested was a 3:1 transformer with a 100R load, so the input impedance will be beyond 200 Ohm. To get the impedance I provide voltage and current measurements to the Bode Plot II system, and use the Vout/Vin display (Vin represents current for this measurement) and a linear display on the y-axis.

These measurements work as expected, but since the input impedance is beyond 200 Ohm for the transformer, the graph disappears outside the plot area. I am forced to either manipulate the probe multiplication factor or use a logarithmic scale. I know I can get the CSV, but it would be nice to have an immediate and correct plot.

Anyone here know if this has been reported? I do use the newest firmware versions.

I have tried it with my connection box. I found the option to set the y-axis linear. You are right, there are limit of +/-200. That is not very nice. If you activate the table of the values, you can see the correct values. I will report this to Siglent.

How is your connection boy set up? Do you have a photo or a schematic? I have the Scope and an SDG2xxx frequency generator, all Scope probes and the generator is connected to earth. How did you solve this problem?

Because I do not understand fully this setup (bolded in quote) I only can "blind" ask... is it possible to solve or help this situation so that also set BodePlot for this real used impedance instead of default 50ohm. This is also adjustable in BP!

[mrprecision]

The problem is not because of the impedance measuring. It is a bug in the BodePlotII function.

For example, if you make a Bodeplot of an amplifier with a gain for example of 300 and use in the Bodeplot a linear y-axis scaling, you should see the gain of 300 in the diagram. But the Diagram is limited to a gain of -200 to +200, so the curve is outside the diagram. In the list table the values a shown correct. The limit of -200 and +200 should be eliminated and the auto scaling of the linear y-axis should be fixed. The logarithmic scaling works fine, maybe there are also limits.

So it is not a problem with the impedance measurement over the frequency, witch works fine. I only saw that problem there yet, because I had no amplifier with this gain. I still prefere the double logarithmic scaling, so capacitors for example are a straight line.

Maybe we could discuss here the adaption boxes for impedance measurements to optimize that.

[mrprecision]

The problem is not because of the impedance measuring. It is a bug in the BodePlotII function.

For example, if you make a Bodeplot of an amplifier with a gain for example of 300 and use in the Bodeplot a linear y-axis scaling, you should see the gain of 300 in the diagram. But the Diagram is limited to a gain of -200 to +200, so the curve is outside the diagram. In the list table the values a shown correct. The limit of -200 and +200 should be eliminated and the auto scaling of the linear y-axis should be fixed. The logarithmic scaling works fine, maybe there are also limits.

So it is not a problem with the impedance measurement over the frequency, witch works fine. I only saw that problem there yet, because I had no amplifier with this gain. I still prefere the double logarithmic scaling, so capacitors for example are a straight line.

Maybe we could discuss here the adaption boxes for impedance measurements to optimize that.

Maybe we could discuss here the adaption boxes for impedance measurements to optimize that?

[graybeard]

For really-high-quality audio power amplifiers, a bode plot of the range 0.1 Hz to, say, 100 Hz will enable a designer to accurately predict the audibility of artifacts coming from attempts to limit the vlf range by steep slope high pass filtering of subsonics.

People building bass guitar amps and high pass filters for them are interested in evaluating the very low frequency response. They often use an HPF to prevent the cone excursions from exceeding safe limits if subsonic information appears at the amplifier inputs. Bass cabs often walk a fine line between being able to generate a high output level at 30 to 60 Hz and blowing up when presented with low frequency noise and often some help from the amp or a filter in front of the amp is needed.

A better question to ask is the 10Hz low limit arbitrary or is it driven some important cost or reliability concern?

If it was just an arbitrary limit then why NOT extend it as far as possible?

People building filters for some scientific applications will want to test at sub 10Hz frequencies. There may not be terribly many such people but again if the limit is arbitrary then it should be removed.

I suspect the 10 Hz low frequency limit is due to the low frequency roll-off of the AC coupling on the scope since it always changes to AC coupling for the bode plot function.   The AC coupled low frequency roll off -3dB point is speced at ≤2 Hz.   For gain flatness you want to be at least a decade above that.

[graybeard]

I verified last night that the Bode Plot II function works great up to 120MHz with my "upgraded" SDS1104X-E and my "upgraded" SDG2042X.

This was my mane reason for upgrading the function generator since it other wave forms are limited to 25MHz regardless of the upper frequency limit for the sine function.

As the frequency increases you need to be far more careful about proper terminations.  The scope needs both a 50 feed through termination and at least a 6dB attenuator for flat response all the way out to 120 MHz.

[rf-loop]

For really-high-quality audio power amplifiers, a bode plot of the range 0.1 Hz to, say, 100 Hz will enable a designer to accurately predict the audibility of artifacts coming from attempts to limit the vlf range by steep slope high pass filtering of subsonics.

People building bass guitar amps and high pass filters for them are interested in evaluating the very low frequency response. They often use an HPF to prevent the cone excursions from exceeding safe limits if subsonic information appears at the amplifier inputs. Bass cabs often walk a fine line between being able to generate a high output level at 30 to 60 Hz and blowing up when presented with low frequency noise and often some help from the amp or a filter in front of the amp is needed.

A better question to ask is the 10Hz low limit arbitrary or is it driven some important cost or reliability concern?

If it was just an arbitrary limit then why NOT extend it as far as possible?

People building filters for some scientific applications will want to test at sub 10Hz frequencies. There may not be terribly many such people but again if the limit is arbitrary then it should be removed.

I suspect the 10 Hz low frequency limit is due to the low frequency roll-off of the AC coupling on the scope since it always changes to AC coupling for the bode plot function.   The AC coupled low frequency roll off -3dB point is speced at ≤2 Hz.   For gain flatness you want to be at least a decade above that.

This AC response in Siglent these models have quite low f corner.  Data sheet do not tell lot, only rough ≤2 Hz -3dB.

Here attached one individual scope response. I have fast checked roughly some other individuals previously and they looks like in same ballpark. 10Hz low limit in SFRA is imho ok for this response.  It is, imho,  best that this BodePlot freq selective receiver is AC coupled.

Bode plot upper limit 120MHz is bit too high but if users know its limits it is still nice have this upper limit than half of it.

---

Inside SDG2000X is possible to tweak some other wfm limits but mostly result is way or other bad.
Of course example if rise triangle upper limit it can do... it can do lot. But... linearity is not then what is told in data sheet and as can see have done in some elcheapo generators due to fact they just want show higher number in data sheet. Also some other limits can break... but always there is then some negative side effect. Limits are just compromise between many variable things.
I have not done these experimentals with SDG2000X But with 1000X. What is - if think system software - very very close relatives.






One random individual SDS1104X-E, 0 - 10Hz fresponse when AC coupled.

[rf-loop]

As the frequency increases you need to be far more careful about proper terminations.  The scope needs both a 50 feed through termination and at least a 6dB attenuator for flat response all the way out to 120 MHz.

It is pity we do not have feed thru terminators what are matched for oscilloscope reactive inputs so that terminator input looks  good 50ohm impedance over whole freq range instead of only for "DC" or near DC like audio etc.

Who will start make these kind of  tunable feed thru terminators for 1M xC xL inputs in oscilloscopes. I do not believe any scope manufacturer start do scopes what have real 50 ohm input impedance when we talk these cheap oscillocopes. Because if they do there need do whole other parallel input stage for this and not just relay connected parallel resistor to ground from input center line.

[tautech]

Siglent BP II App Note:
https://siglentna.com/wp-content/uploads/dlm_uploads/2019/05/Measuring-Power-Supply-Control-Loop-Bode-Plot-with-Bode-Plot-%E2%85%A1.pdf

[pope]

Please excuse my ignorance but I've been trying to run a simple bode plot of a lowpass filter (R=16Ohm, C=01.uF) with an Fc=100kHz.

I am using the 1104x-e with a sdg1032x and I'm having the following problem...

If I use only out1 of the AWG with a T-bar the results look fine. However if I try to use both channels of the AWG (with the tracking mode ON) the Fc is around 25kHz instead of the correct 100kHz.

Anyone knows what am I doing wrong? I've spent a lot of time yesterday and today fighting with my lack of knowledge and so far I'm loosing this battle...

[rf-loop]

Please excuse my ignorance but I've been trying to run a simple bode plot of a lowpass filter (R=16Ohm, C=01.uF) with an Fc=100kHz.

I am using the 1104x-e with a sdg1032x and I'm having the following problem...

If I use only out1 of the AWG with a T-bar the results look fine. However if I try to use both channels of the AWG (with the tracking mode ON) the Fc is around 25kHz instead of the correct 100kHz.

Anyone knows what am I doing wrong? I've spent a lot of time yesterday and today fighting with my lack of knowledge and so far I'm loosing this battle...

Is it fun that 50 ohm (generator source impedance) + 16 ohm is 66 ohm. With this R  and 0.1uF C it give bit over 24Hz...   at least it’s a really funny coincidence, is it. Think about it, at least.   

I don’t want to take a further stand because I haven’t seen (whole setup) the whole reality you have in every factor involved.

[pope]

Please excuse my ignorance but I've been trying to run a simple bode plot of a lowpass filter (R=16Ohm, C=01.uF) with an Fc=100kHz.

I am using the 1104x-e with a sdg1032x and I'm having the following problem...

If I use only out1 of the AWG with a T-bar the results look fine. However if I try to use both channels of the AWG (with the tracking mode ON) the Fc is around 25kHz instead of the correct 100kHz.

Anyone knows what am I doing wrong? I've spent a lot of time yesterday and today fighting with my lack of knowledge and so far I'm loosing this battle...

Is it fun that 50 ohm (generator source impedance) + 16 ohm is 66 ohm. With this R  and 0.1uF C it give bit over 24Hz...   at least it’s a really funny coincidence, is it. Think about it, at least.   

I don’t want to take a further stand because I haven’t seen (whole setup) the whole reality you have in every factor involved.

Of course , I feel stupid I missed that... Thanks for pointing it out!

However, I still don't understand why with. single channel and a T-bar,  the results were correct.

PS. I just tried with some more reasonable values (R=1kOhm, C0.1uF) and in both cases I got the correct results, Fc=1kHz.

[rf-loop]

Please excuse my ignorance but I've been trying to run a simple bode plot of a lowpass filter (R=16Ohm, C=01.uF) with an Fc=100kHz.

I am using the 1104x-e with a sdg1032x and I'm having the following problem...

If I use only out1 of the AWG with a T-bar the results look fine. However if I try to use both channels of the AWG (with the tracking mode ON) the Fc is around 25kHz instead of the correct 100kHz.

Anyone knows what am I doing wrong? I've spent a lot of time yesterday and today fighting with my lack of knowledge and so far I'm loosing this battle...

Is it fun that 50 ohm (generator source impedance) + 16 ohm is 66 ohm. With this R  and 0.1uF C it give bit over 24Hz...   at least it’s a really funny coincidence, is it. Think about it, at least.   

I don’t want to take a further stand because I haven’t seen (whole setup) the whole reality you have in every factor involved.

Of course , I feel stupid I missed that... Thanks for pointing it out!

However, I still don't understand why with. single channel and a T-bar,  the results were correct.

PS. I just tried with some more reasonable values (R=1kOhm, C0.1uF) and in both cases I got the correct results, Fc=1kHz.

Think about it.  Think where from come signal what is reference. 
Think this generator internal R1 and then your external RC circuit R2. 
Bode Plot reference channel  come from this point between R1 and R2 and is also input to your RC what is just this R2 and then C.

In this single channel method, the internal resistor R1 certainly acts  but since the reference point is after it, its effect is eliminated because BP compares only DUT in and DUT out.
This does not happen with 2 channel operation because your RC will not load this other channel what is used only as a reference.
The two-channel method has some important advantages, but also some disadvantages, and one disadvantage is exactly what happens in this case.

[pope]

Please excuse my ignorance but I've been trying to run a simple bode plot of a lowpass filter (R=16Ohm, C=01.uF) with an Fc=100kHz.

I am using the 1104x-e with a sdg1032x and I'm having the following problem...

If I use only out1 of the AWG with a T-bar the results look fine. However if I try to use both channels of the AWG (with the tracking mode ON) the Fc is around 25kHz instead of the correct 100kHz.

Anyone knows what am I doing wrong? I've spent a lot of time yesterday and today fighting with my lack of knowledge and so far I'm loosing this battle...

Is it fun that 50 ohm (generator source impedance) + 16 ohm is 66 ohm. With this R  and 0.1uF C it give bit over 24Hz...   at least it’s a really funny coincidence, is it. Think about it, at least.   

I don’t want to take a further stand because I haven’t seen (whole setup) the whole reality you have in every factor involved.

Of course , I feel stupid I missed that... Thanks for pointing it out!

However, I still don't understand why with. single channel and a T-bar,  the results were correct.

PS. I just tried with some more reasonable values (R=1kOhm, C0.1uF) and in both cases I got the correct results, Fc=1kHz.

Think about it.  Think where from come signal what is reference. 
Think this generator internal R1 and then your external RC circuit R2. 
Bode Plot reference channel  come from this point between R1 and R2 and is also input to your RC what is just this R2 and then C.

In this single channel method, the internal resistor R1 certainly acts  but since the reference point is after it, its effect is eliminated because BP compares only DUT in and DUT out.
This does not happen with 2 channel operation because your RC will not load this other channel what is used only as a reference.
The two-channel method has some important advantages, but also some disadvantages, and one disadvantage is exactly what happens in this case.

That makes sense. Thank you very much!

What would you consider as advantages in the two-channel method that the single channel doesn't have?

[rf-loop]

Please excuse my ignorance but I've been trying to run a simple bode plot of a lowpass filter (R=16Ohm, C=01.uF) with an Fc=100kHz.

I am using the 1104x-e with a sdg1032x and I'm having the following problem...

If I use only out1 of the AWG with a T-bar the results look fine. However if I try to use both channels of the AWG (with the tracking mode ON) the Fc is around 25kHz instead of the correct 100kHz.

Anyone knows what am I doing wrong? I've spent a lot of time yesterday and today fighting with my lack of knowledge and so far I'm loosing this battle...

Is it fun that 50 ohm (generator source impedance) + 16 ohm is 66 ohm. With this R  and 0.1uF C it give bit over 24Hz...   at least it’s a really funny coincidence, is it. Think about it, at least.   

I don’t want to take a further stand because I haven’t seen (whole setup) the whole reality you have in every factor involved.

Of course , I feel stupid I missed that... Thanks for pointing it out!

However, I still don't understand why with. single channel and a T-bar,  the results were correct.

PS. I just tried with some more reasonable values (R=1kOhm, C0.1uF) and in both cases I got the correct results, Fc=1kHz.

Think about it.  Think where from come signal what is reference. 
Think this generator internal R1 and then your external RC circuit R2. 
Bode Plot reference channel  come from this point between R1 and R2 and is also input to your RC what is just this R2 and then C.

In this single channel method, the internal resistor R1 certainly acts  but since the reference point is after it, its effect is eliminated because BP compares only DUT in and DUT out.
This does not happen with 2 channel operation because your RC will not load this other channel what is used only as a reference.
The two-channel method has some important advantages, but also some disadvantages, and one disadvantage is exactly what happens in this case.

That makes sense. Thank you very much!

What would you consider as advantages in the two-channel method that the single channel doesn't have?

Here's a little seeds from which can to grow thoughts:


• When using low frequencies and simple objects such as simple RLC type LP, BP and HP filters and so on, just nothing or nearly nothing.
 
• But when we go to higher frequencies, things may concern impedance matching and signal travel time matching.
Example At 100 MHz, depending on the cable type, the travel time can be, for example, around 0.5 ns 10 cm.
With this 100MHz, this alone would mean, for example, a phase shift of about 18 degrees and naturally angle change when frequency change. Then if T-split to oscilloscope 1M 20pF input and to DUT example 50ohm input this branch going into the channel of the oscilloscope can cause quite a problem. At low frequencies it can be forgotten, but at higher frequencies it can look cluttered. Of course, there are ways to reduce problems but it also requires the right supplies, knowledge and experience.

The signal travel time of the reference channel should be the same as the travel time of the cables of the branch that goes through the DUT (If user is interested about phase).
When we split the signal into the DUT input and the BodePlot reference channel (Dut In), the T split can be also a bit problematic in impedance matching and for travel time.


• But then comes a thing that can’t be done at all other than using the generator’s 2-channel. Suppose a DUT causes a constant frequency shift (example as RF mixer).  With the single channel method, its analysis would be impossible.  (It need remember that this Siglent BodePlot is as frequency selective level meter and receiver frequency stepping sweep follow this frequency what it command from generator during frequency stepping sweep)   With the two-channel method, it is possible because you can put the generator in the tracking mode and use frequency offset for that slave channel. FRA do not know this slave channel frequency. It only listen this frequency what generator master channel is commanded to produce. (all three Dut Out channels follow this for measure signal and compare these to Dut In signal what can also think as reference signal (in default it is oscilloscope Ch1 but if user want it can change). 

• We can also meet test situations where we want the voltage level of the reference signal to remain suitably high (example for less noise for better phase detect)  or constant when, for example, DUT have high amplification and / or when we are analyzing something using variable level (level profile) during frequency sweep (Sweep Type / Vari-level).
Also in some times it is perhaps good to use different levels to Reference channel (dut in) for reduce channels Cross Talk effect. (example if we are looking some rf frequency  filter with high stop band attenuation so that reference channel cross talk to DutOut channel does not obscure it from view. 



Also it is important to select: Vout/Vin  or Vout in Display Amplitude menu and in Stimulus menu select right Load value (50, 75, 600, Hi-Z or free variable starting from 50ohm to 100kOhm).

In more complex tests and measurements than RLC filters for audio frequencies, there may be quite a few things to consider when setting up and how to connect the DUT to the system.

[pope]

Please excuse my ignorance but I've been trying to run a simple bode plot of a lowpass filter (R=16Ohm, C=01.uF) with an Fc=100kHz.

I am using the 1104x-e with a sdg1032x and I'm having the following problem...

If I use only out1 of the AWG with a T-bar the results look fine. However if I try to use both channels of the AWG (with the tracking mode ON) the Fc is around 25kHz instead of the correct 100kHz.

Anyone knows what am I doing wrong? I've spent a lot of time yesterday and today fighting with my lack of knowledge and so far I'm loosing this battle...

Is it fun that 50 ohm (generator source impedance) + 16 ohm is 66 ohm. With this R  and 0.1uF C it give bit over 24Hz...   at least it’s a really funny coincidence, is it. Think about it, at least.   

I don’t want to take a further stand because I haven’t seen (whole setup) the whole reality you have in every factor involved.

Of course , I feel stupid I missed that... Thanks for pointing it out!

However, I still don't understand why with. single channel and a T-bar,  the results were correct.

PS. I just tried with some more reasonable values (R=1kOhm, C0.1uF) and in both cases I got the correct results, Fc=1kHz.

Think about it.  Think where from come signal what is reference. 
Think this generator internal R1 and then your external RC circuit R2. 
Bode Plot reference channel  come from this point between R1 and R2 and is also input to your RC what is just this R2 and then C.

In this single channel method, the internal resistor R1 certainly acts  but since the reference point is after it, its effect is eliminated because BP compares only DUT in and DUT out.
This does not happen with 2 channel operation because your RC will not load this other channel what is used only as a reference.
The two-channel method has some important advantages, but also some disadvantages, and one disadvantage is exactly what happens in this case.

That makes sense. Thank you very much!

What would you consider as advantages in the two-channel method that the single channel doesn't have?

Here's a little seeds from which can to grow thoughts:


• When using low frequencies and simple objects such as simple RLC type LP, BP and HP filters and so on, just nothing or nearly nothing.
 
• But when we go to higher frequencies, things may concern impedance matching and signal travel time matching.
Example At 100 MHz, depending on the cable type, the travel time can be, for example, around 0.5 ns 10 cm.
With this 100MHz, this alone would mean, for example, a phase shift of about 18 degrees and naturally angle change when frequency change. Then if T-split to oscilloscope 1M 20pF input and to DUT example 50ohm input this branch going into the channel of the oscilloscope can cause quite a problem. At low frequencies it can be forgotten, but at higher frequencies it can look cluttered. Of course, there are ways to reduce problems but it also requires the right supplies, knowledge and experience.

The signal travel time of the reference channel should be the same as the travel time of the cables of the branch that goes through the DUT (If user is interested about phase).
When we split the signal into the DUT input and the BodePlot reference channel (Dut In), the T split can be also a bit problematic in impedance matching and for travel time.


• But then comes a thing that can’t be done at all other than using the generator’s 2-channel. Suppose a DUT causes a constant frequency shift (example as RF mixer).  With the single channel method, its analysis would be impossible.  (It need remember that this Siglent BodePlot is as frequency selective level meter and receiver frequency stepping sweep follow this frequency what it command from generator during frequency stepping sweep)   With the two-channel method, it is possible because you can put the generator in the tracking mode and use frequency offset for that slave channel. FRA do not know this slave channel frequency. It only listen this frequency what generator master channel is commanded to produce. (all three Dut Out channels follow this for measure signal and compare these to Dut In signal what can also think as reference signal (in default it is oscilloscope Ch1 but if user want it can change). 

• We can also meet test situations where we want the voltage level of the reference signal to remain suitably high (example for less noise for better phase detect)  or constant when, for example, DUT have high amplification and / or when we are analyzing something using variable level (level profile) during frequency sweep (Sweep Type / Vari-level).
Also in some times it is perhaps good to use different levels to Reference channel (dut in) for reduce channels Cross Talk effect. (example if we are looking some rf frequency  filter with high stop band attenuation so that reference channel cross talk to DutOut channel does not obscure it from view. 



Also it is important to select: Vout/Vin  or Vout in Display Amplitude menu and in Stimulus menu select right Load value (50, 75, 600, Hi-Z or free variable starting from 50ohm to 100kOhm).

In more complex tests and measurements than RLC filters for audio frequencies, there may be quite a few things to consider when setting up and how to connect the DUT to the system.

Thank you very much for the comprehensive reply. I'm gonna read your post a few times to digest it

The fact is that I only do audio so I maybe the bode plot measurements are a bit less complicated...

[mawyatt]

• But then comes a thing that can’t be done at all other than using the generator’s 2-channel. Suppose a DUT causes a constant frequency shift (example as RF mixer).  With the single channel method, its analysis would be impossible.  (It need remember that this Siglent BodePlot is as frequency selective level meter and receiver frequency stepping sweep follow this frequency what it command from generator during frequency stepping sweep)   With the two-channel method, it is possible because you can put the generator in the tracking mode and use frequency offset for that slave channel. FRA do not know this slave channel frequency. It only listen this frequency what generator master channel is commanded to produce. (all three Dut Out channels follow this for measure signal and compare these to Dut In signal what can also think as reference signal (in default it is oscilloscope Ch1 but if user want it can change). 

Very powerful technique!!!

Best,

[rf-loop]

With the two-channel method, it is possible because you can put the generator in the tracking mode and use frequency offset for that slave channel.

Clarification. Example with SDG1032X generator.

Go to Utility [CH Copy Coupling] menu.
  For normal Track (same frequency and same amplitude) turn [Track On] and if you need phase offset then in this menu go to [PhaseDev] and adjust.

  For Ch2 tracking Ch1 with user defined offset(s).
  For Ch2 coupled to Ch1 using fixed frequency offset (Siglent language: deviation), leave [Track / Off] and push [Channel Coupling].
  In this Coupling menu set wanted fixed frequency offset (deviation). Select [FreqMode / Deviation] and set value, example 1500Hz.
  Then set [FreqCoup / On] and look that amplitude and phase coupling are Off.
  After this, Ch2 follow Ch1 with fixed frequency offset (deviation) but with amplitude you have set.
  If you want Ch2 follow also Ch1 amplitude just leave AmplDev value zero but turn also [AmpCoup / On].

I am not very satisfied how Siglent have named these. I like more if it is named as offset than deviation.


SDG1000X (as also other Siglent 2 channel SDG's) channels direct track or using channels coupling feature is nice for some things also with BodePlot when use generator two channels with it for some special things.
Frequency fixed freg offset or fixed ratio
Amplitude fixed level offset or fixed ratio
Phase fixed phase offset or fixed ratio
All these can separately turn off or on. All combinations can use.

[pope]

Apologies if this has already been discussed but I can't find any information.

I would like to do the following and I don't know whether it's possible.

I would like to combine/add two signals (eg. on inputs 1 & 2) with the polarity inverted on one input (eg. on input 3) and do a bode plot of the combined signal. Is this possible with the 1104x-e?

Thanks!

[2N3055]

Apologies if this has already been discussed but I can't find any information.

I would like to do the following and I don't know whether it's possible.

I would like to combine/add two signals (eg. on inputs 1 & 2) with the polarity inverted on one input (eg. on input 3) and do a bode plot of the combined signal. Is this possible with the 1104x-e?

Thanks!

In short, no.

[pope]

Apologies if this has already been discussed but I can't find any information.

I would like to do the following and I don't know whether it's possible.

I would like to combine/add two signals (eg. on inputs 1 & 2) with the polarity inverted on one input (eg. on input 3) and do a bode plot of the combined signal. Is this possible with the 1104x-e?

Thanks!

In short, no.

It's a shame. Is any other scope able to do this?

[2N3055]

I don't think any will let you do Bode plot over Math channel. At least not ones I know off..

[pope]

I don't think any will let you do Bode plot over Math channel. At least not ones I know off..

Interesting. I wonder why... thanks for the answer anyway 

[luciof]

I made some tests with an SDS 1104X-E  6.1.37R9 (ext. to 200MHz) and an SDG 2042 X (ext. to 120 MHz).
Bode Plot II works very well within the audio range and more. For higher frequencies, impedance matched fixtures would work best, but this is not always possible and - anyway - better suited instruments would be needed for trustful measurements.

For practical purposes, I think that the supplied PP510 10x probes are fine up to a few tens MHz; better yet, low capacitance active probes would be ideal to minimize DUT loading.

First test: 10x probes on CH1 and CH2 directly clamped to the generator output.

This worked better than expected (to me), usable up to 65 MHz within +/-1 dB.

But, there's a problem.
CH1 and CH2 use the same ADC, and - as expected - there's no appreciabile skew.
The same setup with CH1 and CH3 (each on its own ADC) gives the following plots:

Here the phase begins to visibly change beyond 1+ MHz, due to a delay between CH1 and CH3. From the data table, we read -12.8 deg. @ 39.81 MHz, which corresponds to 12.8/360*1000/39.81 = 0.893 ns (CH1 is delayed with respect to CH3).
After setting up an 890 ps deskew [not sure about the sign] on CH3, this is the new run:

There is [almost] no change from previous plots, meaning that channel deskew is ignored by Bode Plot (or maybe I missed something).
Anyway, almost 1 full ns of skew between channels should never happen, so I attached the probes to the output of a 40 ps risetime L.Bodnar square wave generator to see what happens:

This confirms that CH1 is delayed with respect to CH3, but only by about 100 ps - not easy to evaluate.

Conclusion: Bode Plot II is a very handy and usable feature, but for a proficient use of the phase plot beyond a few MHz, it should be allowed to enter a delay parameter to each scope channel for manual compensation (automatic phase compensation at selected frequencies after a preliminary a test run would be great).

As a side note, the input attenuation (1x, 10x etc.) should be properly set before entering the Bode Plot environment. I see that this setting is quite cumbersome:
1) select the desired channel
2) press button #4 "Probe nnX"
3) press button #1 "Probe nnX"
4) select attenuation using the Adjust knob
5) carefully press the knob without changing the selection
The most used attenuation factors are 1x and 10x by far, so it would be nice to alternate 1x and 10x by repeatedly pressing button #4. This way, selecting 1x or 10x would be much much faster.

That's all... Thanks to anyone who has had the patience to read this stuff 

[tautech]

I made some tests with an SDS 1104X-E  6.1.37R9 (ext. to 200MHz) and an SDG 2042 X (ext. to 120 MHz).

But, there's a problem.
CH1 and CH2 use the same ADC, and - as expected - there's no appreciabile skew.

You would be well advised to study this and following posts to see some ways Skew can be much reduced:
https://www.eevblog.com/forum/testgear/siglent-sds1x04x-e-bodeplot-ii-(sfra)-features-and-testing-(coming)/msg4045984/#msg4045984

[luciof]

Thanks tautech;
I had already read the whole topic before, and specifically the post you pointed out. I also realize that I haven't made it entirely clear what I meant.

To be clear, I'm quite happy with the scope; I'm not criticizing it, but trying to point out some details to improve it further.

Regarding the skew and the related phase plot derating:

1- In my very basic setup, there is no significant skew related to cables and connections; in fact, using a single generator output and two "ADC coupled" scope channels (CH1 & CH2 or CH3 & CH4) the phase plot looks quite good (actually, the plots go haywire beyond 60 MHz, but this is because I clamped both the probe clips to a stub of wire stuck into the generator output and both ground clips clamped to the BNC ground shell. In previous tests with impedance-matched cables, terminations etc. this didn't happen, but anyway the plots were quite the same below 50 MHz, and it's enough for this evaluation).
2- The main issue arises using unrelated channels ( (CH1 or CH2) & (CH3 or CH4) ). In this case I consistently find a phase derating due to a constant delay between the scope channels; in my tests, the calculated delay is around 850-900 ps.
3- At first, one would think it's the skew between the scope channels, but it is unrealistically large and - in fact - the real skew is far smaller (about 100 ps or less, difficult to measure properly and usually negligible). Moreover, setting a deskew on the scope channels seems to make no difference
4- Anyway, in real measurement setups some significant time mismatch is always possible, and it would be very handy to be allowed to enter a compensation (delay value) parameter in Bode Plot II settings
5- In fact, when using two coupled generator outputs for bode plotting (as suggested somewhere to avoid power splitting fixtures), in previous impedance matched tests I found that the generator outputs were quite well matched in both frequency and amplitude, but there was a delay of about 280 ps between them. The only way to practically compensate this, I think, would be a specific compensation parameter (i.e., the delay parameter of point (4)).
6- Finally, I think that this kind of issue is usually underestimated because the main plot is the amplitude (modulo) plot, and often phase plot is discarded after a quick look; neverthless, in more involved works it can be very useful.


That's all for now. Sorry for the numbered layout above: it helped me to better explain my points while struggling to write in English..., and thanks again for your attention.

[Performa01]

Yes, the limited accuracy of phase measurements between the two separate ADCs have been discovered a long time ago, as can be demonstrated by the attached old screenshots from June 2019:

SDS1104X-E_Y-t_Phase_Error

SDS1104X-E_FRA_Phase_Error

These demonstrate how four signals with phase differences of no more than 3.15° in the time domain can be measured as up to 40° in the Bode Plot. Since it is quite obvious that this is a channel skew issue, the fact that the channel Deskew parameter is ignored by the Bode Plot has been discovered back then as well and I’m surprised that we never got a fix.

Maybe there are some restrictions in the HW architecture that prevent an easy solution.

In any case, this does not make the Bode Plot useless, even at high frequencies.

Just restrict measurements to a single ADC whenever you need accurate phase information at frequencies beyond a couple MHz. You lose the ability to plot three channels in parallel, but then again, we should never forget that competing products are limited to a single channel up to 25 MHz or so, hence a single channel up to 120 MHz should still be a major advantage. And there’s still the option of having three channels, even when phase information gets inaccurate above a couple MHz.

Maybe sometimes we just can’t get everything in the cheapest package; at least for the more advanced HW-platforms, Siglent have addressed these issues. Reply #3585 in the SDS2000X Plus thread demonstrates just this:

https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg4370986/#msg4370986

I’m not keen on the idea of introducing a specific correction parameter in the Bode Plot. We want a correlation between time domain and frequency domain (at least in the higher class instruments we can watch the time domain during bode plot), so just using the Deskew parameter that is already there would be the obvious solution. I suspect this is the reason for the phase error in the SDS1004X-E in the first place; the normal y-t operation always needs some compensation for runtime differences anyway – and there it works. If Bode Plot would use these corrected data, there wouldn’t be any problems. For some reason it seems to use the uncorrected RAW data instead.

I’ll try to clarify this.

[luciof]

Yes, the limited accuracy of phase measurements between the two separate ADCs have been discovered a long time ago, as can be demonstrated by the attached old screenshots from June 2019:

SDS1104X-E_Y-t_Phase_Error

SDS1104X-E_FRA_Phase_Error

These demonstrate how four signals with phase differences of no more than 3.15° in the time domain can be measured as up to 40° in the Bode Plot. Since it is quite obvious that this is a channel skew issue, the fact that the channel Deskew parameter is ignored by the Bode Plot has been discovered back then as well and I’m surprised that we never got a fix.

The actual skew we see (3.15° @ 100 MHz) boils down to 97 ps, while the [more or less] 32° @ 100 MHz we see in the plot are about 890 ps, so the "time domain delay" and "bode plot delay" are definitely distinct; moreover, even if I change the deskew, the phase plots don't change anyway.

In any case, this does not make the Bode Plot useless, even at high frequencies.

Just restrict measurements to a single ADC whenever you need accurate phase information at frequencies beyond a couple MHz. You lose the ability to plot three channels in parallel, but then again, we should never forget that competing products are limited to a single channel up to 25 MHz or so, hence a single channel up to 120 MHz should still be a major advantage. And there’s still the option of having three channels, even when phase information gets inaccurate above a couple MHz.

Maybe sometimes we just can’t get everything in the cheapest package; at least for the more advanced HW-platforms, Siglent have addressed these issues. Reply #3585 in the SDS2000X Plus thread demonstrates just this:

https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg4370986/#msg4370986

I agree, the system is very well usable within its limits, but I don't see this scope as a "cheap" one, rather a "low cost, high performance/cost ratio instrument". I think this should translate to the [reasonably] best exploitation of its hardware combined with a well honed UI. While this is still a cost, I would see it more as an investment, because a degree of sloppiness in a $500 device might be also expected in a $5000 one from the same firm [of course this is not  the case, just to make the point ]

I’m not keen on the idea of introducing a specific correction parameter in the Bode Plot. We want a correlation between time domain and frequency domain (at least in the higher class instruments we can watch the time domain during bode plot), so just using the Deskew parameter that is already there would be the obvious solution. I suspect this is the reason for the phase error in the SDS1004X-E in the first place; the normal y-t operation always needs some compensation for runtime differences anyway – and there it works. If Bode Plot would use these corrected data, there wouldn’t be any problems. For some reason it seems to use the uncorrected RAW data instead.

Here I don't agree.
Ideally, we would sample both input and output of the DUT in the exact same instant; this is obviously not possible, but if this timing error is reasonably constant, we can take it into account very easily when doing the math. For sure, this delay is not part of the results we need and - if well carachterized - can and should be cancelled out.
Concluding (and reiterating):
First, it's true that only in very rare occasions more than 2 channels are needed, and even then, when accurate and reliable plots beyond - say - 10 MHz are required, they'll need very accurate setups and probably something more than a generic scope and generator. But why give up something the hardware is well capable of doing, with only minor firmware adjustments? (And anyway, I see the abnormal and unmodifiable skew in bode plot more as a bug than a missing feature; if the skew was the actual one we see in time domain it might be good enough without compensation).
Second, a "delay" parameter in the Bode Plot environment would take care very well of the issue we are talking of, and allow to compensate for non-instrument related delays. Two examples come to mind:
1) I have the following setup:
generator --> 50 ohm cable --> DUT (with 50 ohm input and output Z) --> 50 ohm cable --> 50 ohm pass-thru terminator --> scope BNC
the output channel is OK; now I need to also connect the DUT input to the scope; below - say - 100 MHz, I think the best way is to clip an active probe (only 1-2 pF loading) to the DUT input. But now we'll have a "large" delay (>5 ns for sure) which would make the phase plot practically unusable
2) Using an SDG2000X generator with coupled channels to make my connections simpler (one output to the DUT input, the other one to the scope input channel. In my case this adds up a further delay of about 300 ps (see picture)

In both examples, a simple user parameter would cleanly solve the problem.

To me, this is a fine instrument, and not "for its price", but I would better say "within its class and specifications". And I think it could be improved further with minor refinements.

[rf-loop]

Yes, the limited accuracy of phase measurements between the two separate ADCs have been discovered a long time ago, as can be demonstrated by the attached old screenshots from June 2019:

SDS1104X-E_Y-t_Phase_Error

SDS1104X-E_FRA_Phase_Error

These demonstrate how four signals with phase differences of no more than 3.15° in the time domain can be measured as up to 40° in the Bode Plot. Since it is quite obvious that this is a channel skew issue, the fact that the channel Deskew parameter is ignored by the Bode Plot has been discovered back then as well and I’m surprised that we never got a fix.

Maybe there are some restrictions in the HW architecture that prevent an easy solution.

In any case, this does not make the Bode Plot useless, even at high frequencies.

Just restrict measurements to a single ADC whenever you need accurate phase information at frequencies beyond a couple MHz. You lose the ability to plot three channels in parallel, but then again, we should never forget that competing products are limited to a single channel up to 25 MHz or so, hence a single channel up to 120 MHz should still be a major advantage. And there’s still the option of having three channels, even when phase information gets inaccurate above a couple MHz.

Maybe sometimes we just can’t get everything in the cheapest package; at least for the more advanced HW-platforms, Siglent have addressed these issues. Reply #3585 in the SDS2000X Plus thread demonstrates just this:

https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg4370986/#msg4370986

I’m not keen on the idea of introducing a specific correction parameter in the Bode Plot. We want a correlation between time domain and frequency domain (at least in the higher class instruments we can watch the time domain during bode plot), so just using the Deskew parameter that is already there would be the obvious solution. I suspect this is the reason for the phase error in the SDS1004X-E in the first place; the normal y-t operation always needs some compensation for runtime differences anyway – and there it works. If Bode Plot would use these corrected data, there wouldn’t be any problems. For some reason it seems to use the uncorrected RAW data instead.

I’ll try to clarify this.

Channels Skev adjustment works also in FRA (least in my old SDS1004X-E) but way Ch Skew adjust works is really poor.
Have not tested now enough, but when I found my old handwritten piece of paper ("post it") note. I tried it just but due to other things very busy only very limitedly and quikly(=error warning!).

My SDS FW is 6.1.37R8

Looks somehow (when FRA in use) that it is still so that  when ADC's are interleaved (true ADC speed 1GSa/s) Skev adjust resolution is 1ns and when ADC's non interleaved mode (true ADC speed 500MSa/s) resolution is 2ns! what resolutions are really enormously too rough when we work higher frequencies (example over 1MHz. @1MHz  1ns responds 0.36 degree and @60MHz 21.6 degree what also was masured result here - naturally because time shift IS 1ns in this case.).
It need remember what are sample intervals. This is only true time resolution! There is nothing below 1ns resolution (except fine intepolation between true raw samples)


In quick and "dirty" test I use 1-60MHz sweep.
FRA:
Source generator Ch1. This was splitted with matched cable pair to oscilloscope ref CH1 and "dut out" CH3
If CH1 and CH3 alone active and all CH Settings all zero.  Maximum phase error around 0.4 degree
If I adjust then CH3 Skew nothing happen until Skev is 1ns. With this Skew result is roughly +22 degree error.

But then FRA settings all same (just Ch1 and Ch3 etc):
Oscilloscope all 4 channels in use. (2 and 4 not FRA use)
Now ADC's work at 500MSa/s (I do not here talk anything about decimated samplerates, it do not matter here)
CH's Skew all 0.   Result at 60MHz.  Phase error roughly -22 degree.

Okay, then I think I adjust Ch3 Skew. I set it to 1.0ns   Result: nothing happen, FRA displayed same roughly -22 degree phase at 60MHz.

Next I set Ch3 Skew to 2.0ns. 
Result:  Phase error at 60MHz is now roughly +22 degree.

I can assume that if I can set Skev to 1.0ns it is quite same as originally when only two channels are in use and 1GSa/s
But now 1ns set is ignored (it really looks like resolution is 2ns  (sample interval without fine interpolation)

When Skew only works every 1ns or 2ns, it's like a 22" spanner on a watchmaker's workbench.
Of course if one do only 1kHz or 10kHz things... it is different case.

Why there is this 1ns shift between ADC's interleaved and non interleaved mode. Even if Skew can not work with fine interpolation in FRA,  still this 1ns  BUG between ADC's interleaved/non interleaved mode is imho BUG.
 
Naturally it can compensate example using 1ns delay. Example ~20cm RG223.
Set of fixed delay lines is always good to have (adjustable delays/phase shifters even better - and expensive).


It is bit surprise this BUG is still there! 
.... somehow as if old jobs are left unfinished when you jump into a new job and think "time to take care of problems". Time doesn't take care of them. These unfinished jobs still have to be taken care of fully, and that requires doing the right thing, not just pretending. After all, bosses often want their workers hands to wave a lot, but they forget that quality is more important than quantity. Insufficient quality, however, sometimes later pulls the rug from under your feet.

[mawyatt]

Not knowing exactly how the instrument takes the sample and in what order if in interleave or sequential mode, so this is just a "What if" statement.

If the samples of "Input" and "Output" are interchanged in time sequence for a single averaged "Sample Point" on the Bode Plot it seems the time skew would be removed in the averaging for a single Sample Point. Think the Bode Plot does use multiple samples to render a final Sample Point to improve Sample Point fidelity, so alternately swapping actual In/Out sample time sequence then averaging seems reasonable.

Best,

[Performa01]

Channels Skev adjustment works also in FRA (least in my old SDS1004X-E) but way Ch Skew adjust works is really poor.
Have not tested now enough, but when I found my old handwritten piece of paper ("post it") note. I tried it just but due to other things very busy only very limitedly and quikly(=error warning!).

My SDS FW is 6.1.37R8

Looks somehow (when FRA in use) that it is still so that  when ADC's are interleaved (true ADC speed 1GSa/s) Skev adjust resolution is 1ns and when ADC's non interleaved mode (true ADC speed 500MSa/s) resolution is 2ns! what resolutions are really enormously too rough when we work higher frequencies (example over 1MHz. @1MHz  1ns responds 0.36 degree and @60MHz 21.6 degree what also was masured result here - naturally because time shift IS 1ns in this case.).
It need remember what are sample intervals. This is only true time resolution! There is nothing below 1ns resolution (except fine intepolation between true raw samples)

Okay, this makes sense now.

Of course, both the normal DSO operation (y-t) and the Bode Plot use the raw sample data as basis.

The y-t display uses the deskew parameter to fine positipon the trace with regard to the trigger point. The resolution for this can be as fine as we like - it's just a "graphical" operation.

Bode Plot could do the very same. Instead of positioning a trace in a graph window, it would have to add the Deskew time to the phase measurement. Really simple.

[rf-loop]

...it would have to add the Deskew time to the phase measurement. Really simple.

And because this is so simple it is totally amazing it is not already done. SDS1004X-E was Siglent first model where FRA was launched. And still this channels Skew is missing and now we live year 2022.

But then, my opinion is that it is perhaps better if we don not use oscilloscope channels Skew parameter at all in FRA, let these be scope (xt) alone.
I like if FRA have its own channels time correction adjustments (FRA channels Skew (perhaps oscilloscope channels Skew ignored)
I have couple of strong arguments for that, which I will not present in this envinronment now. I'm just saying simply that the FRA of all models needs to be develop better in terms of a few functions and UI for better usabiolity and for performance.

But naturally "first aid" simple solution is: just  correct FRA phase calculus with oscilloscope user adjusted Skew (using set parameter full resolution)


Different other thing, BUG (in SDS1004X-E ) is that there is this 1ns time error related to 2 separate ADC's. This is not based to different signal travel time. It is some kind of ADC data stream handling bug in FRA.  Also this can ask why this bug is still there.

[gf]

1) I have the following setup:
generator --> 50 ohm cable --> DUT (with 50 ohm input and output Z) --> 50 ohm cable --> 50 ohm pass-thru terminator --> scope BNC
the output channel is OK; now I need to also connect the DUT input to the scope; below - say - 100 MHz, I think the best way is to clip an active probe (only 1-2 pF loading) to the DUT input.

Active probe is likely overkill here, since the loading at the DUT input does not matter. Whatever voltage appears at the probe tip, it is always the input voltage of the DUT, and the Bode plot is the ratio between output and input voltage. So the Bode plot appears as if the DUT were driven by an ideal voltage source. OTOH, loading at the DUT output does matter if the DUT's output impedance is not zero.

[luciof]

Yes, you're right, I overdid it. In this case (even at the 120 MHz max frequency) a regular 10x passive probe would be enough, rather taking care to not create ground loops or other disturbances (which would be true for any kind of probing)..

[mawyatt]

Different other thing, BUG (in SDS1004X-E ) is that there is this 1ns time error related to 2 separate ADC's. This is not based to different signal travel time. It is some kind of ADC data stream handling bug in FRA.  Also this can ask why this bug is still there.

If this is a time limitation in the FPGA, swapping the ADCs between which is first to acquire and last to acquire, then averaging the readings seems at it would eliminate this time limitation and render a average reading of the ADC samples.

Best,

[Warpspeed]

Bode plots of passive filters and broadband amplifiers is not that difficult because the signals being measured are going to be fairly clean. 
Its just a case of having sufficient available dynamic range, and a nice low noise floor.

The situation changes pretty dramatically when trying to characterize the feedback loop in a very noisy switching power supply. This is not an uncommon application these days, in fact for many power electronics designers, it would be the ONLY application equipment like this would ever be used for.

Can anyone demonstrate resolving millivolt and sub millivolt signals in the presence of perhaps volts of extremely fast rise time noise spikes and broad band hash?
Will it do it ?
Can it do it ?

[FunJumper]

Hi Guy.

Can the Bode II setup be saved from within the Bode II application on SDS1104x-e? I only see a save data in csv. How can the Bode II setup be saved to external USB?

Thanks.
FunJumper

[tautech]

Hi Guy.

Can the Bode II setup be saved from within the Bode II application on SDS1104x-e? I only see a save data in csv. How can the Bode II setup be saved to external USB?

Thanks.
FunJumper

With latest firmware Bode plot settings are autosaved and returned from last use.

There is no way to save explicitly the Bode plot settings although using the Save/Recall Setup to USB should also capture Bode plot settings.

[jeraymond]

What does the "Arbitrary dB" unit reference to in the Display -> Amplitude settings? Is it some unknown arbitrary reference level or is there some way to set what it references (e.g. 1V or something)?

[pope]

What does the "Arbitrary dB" unit reference to in the Display -> Amplitude settings? Is it some unknown arbitrary reference level or is there some way to set what it references (e.g. 1V or something)?

Did you figure it out? I'm also not sure what the "Arbitrary dB" is.

On a different note, is there any way of choosing which trace you want to be visible? It seems to me that both the gain and the phase traces are always visible. AFAIK the sds2000x plus has this option but what about the SDS1x04X-E ? Is this feature missing?

[jeraymond]

What does the "Arbitrary dB" unit reference to in the Display -> Amplitude settings? Is it some unknown arbitrary reference level or is there some way to set what it references (e.g. 1V or something)?

Did you figure it out? I'm also not sure what the "Arbitrary dB" is.

On a different note, is there any way of choosing which trace you want to be visible? It seems to me that both the gain and the phase traces are always visible. AFAIK the sds2000x plus has this option but what about the SDS1x04X-E ? Is this feature missing?

Didn't really figure it out, but the values for Arbitrary dB seem the same as dBV. I'm not seeing an option to disable either trace and always see both.

[pope]

What does the "Arbitrary dB" unit reference to in the Display -> Amplitude settings? Is it some unknown arbitrary reference level or is there some way to set what it references (e.g. 1V or something)?

I'm not seeing an option to disable either trace and always see both.

Yes, it's very annoying and I really don't see why the excluded this option for the 1104x-e. This sucks.

[WPE]

I am considering a Siglent SDS1202XE with SDG2042X - excited about the BODE PLOT II function and FFT along with a great oscilloscope - it would be my first new bench equipment in many years. 

My main initial application will be antique radio 456 kHz IF alignments with 2 and 3 stage variable BW IF's.  I've had some difficulty with my HP 141T spectrum analyzer and its 8443 tracking generator - and haven't found time to look into it.  I wanted "as-found" measurements before I start on these radios.  (I don't use that on simpler radios.) 

How practical is BODE PLOT II for a detailed look at these IF's?  I wonder if I would use sweep with demodulator probe to do real-time alignments, then follow up with the BP2 - or has anyone tried twiddling in small steps between waiting for another BP2 plot? 

FFT adds another dimension to it - would the FFT also be practical for a detailed look at these IF bandpasses?  Perhaps with noise input? 

I've read you can't really "replace" a good spectrum analyzer with BP2 in a multifunction "do-it-all" instrument - would I be much better off attending to my old HP141T combo for radio IF's?  (Then I would be curious about the phase data I could have had from BP2!) 

Or would this Siglent combo be a really good approach to this task?   

[BillyO]

I'm not a tube guy myself, but if you can attach the equipment safely to the DUT it should work fine.

One suggestion though.  The SDG2042X seems like a bit of overkill if this is your main use case.  For a bit less money than the two you are looking at you could get an SDS2104XP scope and enable the internal 25MHz AWG.  This scope will also do the Bode plotting, has 4 channels, a much larger touch enabled screen, can use a mouse & keyboard, has more triggering options, has all the same serial decoding and can be enabled for more, has more advanced measurement functions, has more advanced math functions, has higher vertical resolution (10-Bit vs 8-bit) and can be set to work up to 500MHz.

Just something to consider.

Either way, I think you will be pleased.

[tautech]

I am considering a Siglent SDS1202XE with SDG2042X - excited about the BODE PLOT II function and FFT along with a great oscilloscope - it would be my first new bench equipment in many years. 

The 2ch SDS1202X-E does not have BP as part of its feature set, maybe instead you meant SDS1204X-E ?

One suggestion though.  The SDG2042X seems like a bit of overkill if this is your main use case.  For a bit less money than the two you are looking at you could get an SDS2104XP scope and enable the internal 25MHz AWG. 

Actually the SDS2000X Plus range has an optional inbuilt 50 MHz AWG.

WPE, if as BillyO points out you instead consider a 2kX Plus do it soon before their $400 off promotion finishes at years end.
https://siglentna.com/news-article/sds2000x-plus-super-phosphor-oscilloscopes-promotions/

[WPE]

Sorry - yes - an SDG1204XE.  I did look hard at the $400 off deal - but figured the '1204 was what I wanted. 

[tautech]

Sorry - yes - an SDG1204XE.  I did look hard at the $400 off deal - but figured the '1204 was what I wanted.

Nah you got it wrong again SDS = Siglent Digital Scope whereas SDG = Siglent Digital Generator. 

[WPE]

I did it again - must need more sleep!  Thanks - SDS1204XE.