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Offline noreply

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Rigol DSG815 - testing feedback and comments
« on: July 06, 2020, 04:21:02 pm »

I have been fortunate to have a NEW Rigol DSG815 made available to me for testing purposes  :)


I want to take this opportunity to invite any forum members who are interested in RF Signal Generators - to make some 'testing' suggestions while I am reviewing this unit.

From my experience - there have been very little comments on the forum regarding the actual performance / use of the DSG815  :(

The only 'hands-on' has been Dave's brilliant teardown on the 815 some time ago   :-+

I was very impresses at the 'clean' build quality and clever RF design as Dave highlighted so well - it looked like a extremely high quality unit, and this was my inspiration in looking deeper to evaluate the actual 'use / performance' of this device before making a purchasing decision (the SSG2030x as the alternative).

So here we are ...

So far I am impressed at the build quality - and initial testing has shown solid results - well within the published specifications.

If anybody has some testing which they would like me to do - then please make a suggestion  :popcorn:


Keeping in mind I can only do some simple things at this moment in time.


I have a SVA1032x and a Rigol MSO5350 at my disposal to complement the testing.


As I make some of my own testing - I will post my results here


Hope everyone interested in purchasing a new RF Signal Generator will find this thread useful  ;)
 

Offline noreply

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Re: Rigol DSG815 - testing feedback and comments
« Reply #1 on: July 06, 2020, 08:51:51 pm »
Testing
 
Frequency / Amplitude / Harmonics

The specifications for the Rigol DSG815 are …

Frequency

Stability with internal oscillator is <2ppM
So, @100Mhz we should not have a frequency deviation of < 200Hz
So, @500Mhz we should not have a frequency deviation of < 1KHz
So, @1000Mhz we should not have a frequency deviation of < 2KHz
So, @1500Mhz we should not have a frequency deviation of < 3KHz


Amplitude

Absolute Level Uncertainty
Temperature range: 20℃ to 30℃

For Amplitude range between +13 dBm to -60 dBm
At a frequency Range between 100 kHz ≤ f ≤ 3.6 GHz
The Amplitude can deviate by ≤ 0.9 dB, ≤ 0.5 (typ.)

For an Amplitude Range between -60 dBm to -110 dBm
At a frequency Range between 100 kHz ≤ f ≤ 3.6 GHz
The Amplitude can deviate by  ≤ 1.1 dB, ≤ 0.7 (typ.)

Harmonics

CW mode
For Frequency range of 1 MHz ≤ f ≤ 3.6 GHz
At an Amplitude level of ≤ +13 dBm
The Harmonics should be < -30 dBc



My Test Findings

Using a direct connection from DSG815 to SVA1032x with > 6GHZ low loss cable

At 100MHz , 20dBm Amplitude (DSG815)
(this is OUTSIDE PUBLISHED SPECIFICATIONS which are limited to <13dBm)

SVA1032x Resultant measurements are
Frequency = 100MHz
Within Specifications (spot-on)

Amplitude = 19.63dBm
Specification states typical < 0.5dBm error
Conclusion DSG815 well within Specifications

Harmonics
1st 2nd Harmonic -20.14dBm
This is outside the specifications of < 30dBm
BUT keep in mind we are operating at 20dBm Amplitude setting
which is outside the < 13dBm Specification


At 100MHz , 13dBm Amplitude (See 13dbm.png)
SVA1032x Resultant measurements are
Frequency = 100MHz
Within Specifications (spot-on)

Amplitude = 12.66dBm
Deviation was -0.34dBm
Specification states typical < 0.5dBm error
Conclusion DSG815 well within Specifications

Harmonics
1st 2nd Harmonic -34.13dBm
This is inside the specifications of < 30dBc

At 100MHz , 0dBm Amplitude (See 0dbm.png)
SVA1032x Resultant measurements are
Frequency = 100MHz
Within Specifications (spot-on)

Amplitude = -0.27dBm
Deviation was -0.27dBm
Specification states typical < 0.5dBm error
Conclusion DSG815 well within Specifications

Harmonics
1st 2nd Harmonic -47.08dBm
This is inside the specifications of < 30dBc



At 100MHz , -10dBm Amplitude (See -10dbm.png)
SVA1032x Resultant measurements are
Frequency = 100MHz
Within Specifications (spot-on)

Amplitude = -10.35dBm
Deviation was -0.35dBm
Specification states typical < 0.5dBm error
Conclusion DSG815 well within Specifications

Harmonics
1st 2nd Harmonic -52.94dBm
This is well inside the specifications of < 30dBc


At 100MHz , -20dBm Amplitude (See -20dbm.png)
SVA1032x Resultant measurements are
Frequency = 100MHz
Within Specifications (spot-on)

Amplitude = -20.31dBm
Deviation was -0.31dBm
Specification states typical < 0.5dBm error
Conclusion DSG815 well within Specifications

Harmonics
1st 2nd Harmonic -53.19dBm
This is inside the specifications of < 30dBc



At 100MHz , -110dBm Amplitude (See -110dbm.png)
SVA1032x Resultant measurements are
Frequency = 100MHz
Within Specifications (spot-on)

Amplitude = -110.56dBm
Deviation was -0.56dBm
Specification states typical < 0.5dBm error but can be <0.9dBm
Conclusion DSG815 well within Specifications

Harmonics
1st 2nd Harmonic – it’s below the noise floor of the SVA at -142.79dBm
A tribute to the Siglent SVS1032x – and its low noise floor of -142dBm well done!
This is inside the specifications of < 30dBc

OK , without going through ALL of the individual results here is summary for other frequencies …

10dbm at 500Mhz (see 500mhz @ 10dbm.png)
Frequency 500.2666667MHz
Deviation is 2.66KHz – acceptable limit is 1KHz (I strongly suspect the SVA in error here because of the LARGE frequency span in measurement)
Amplitude = 9.65dbm – well within spec
1st 2nd Harmonic = -31.25dbm – well within spec


0dbm at 500MHz (see 500mhz @ 0dbm.png)
Frequency 499.536667MHz
Deviation is 4.633kHz – acceptable limit is 1KHz (I strongly suspect the SVA in error here because of the LARGE frequency span in measurement)
Amplitude = -0.31dbm – well within spec
1st 2nd Harmonic = -40.86dbm – well within spec


-110dbm at 500MHz (see 500mhz @ -110dbm.png)
Frequency 500MHz
Deviation is 0kHz – acceptable limit is 1KHz
Amplitude = -110.64dbm – well within spec
1st 2nd Harmonic – it’s below the measured noise floor of the SVA at -135.36dBm

See 1ghz @ 10dbm.png  (results are once again well within specs)
See 1ghz @ 0dbm.png  (results are once again well within specs)
See 1ghz @ -110dbm.png  (results are once again well within specs)
See  1.5ghz @ 10dbm.png  (results are once again well within specs)
See  1.5ghz @ 0dbm.png  (results are once again well within specs)
See  1.5ghz @ -110dbm.png  (results are once again well within specs)


Conclusion

There was a consistent error of approx. 0.3dbm (well within the specifications) in the Amplitude at 100MHz measurements – this is most likely the ‘loss’ in the cable.

All other measurements are well within the specifications of both instruments 

So the Rigol DSG815 is true to its specifications with regard to Frequency / Amplitude / Harmonics


More Testing to follow soon ...
« Last Edit: Yesterday at 09:38:35 am by noreply »
 
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Offline TurboTom

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Re: Rigol DSG815 - testing feedback and comments
« Reply #2 on: July 06, 2020, 08:59:17 pm »
Seems like you're mixing up dBm and dBc in your harmonics tests.

@ 100MHz 20dBm, a harmonics level of -20dBm is still within Rigol's specs of better than -30dBc, namely -40dBc.

Anyway, interesting tests that you're doing there, I wish I had an excuse for spending the money on such a generator...
 

Offline noreply

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Re: Rigol DSG815 - testing feedback and comments
« Reply #3 on: July 06, 2020, 09:55:42 pm »
Seems like you're mixing up dBm and dBc in your harmonics tests.

@ 100MHz 20dBm, a harmonics level of -20dBm is still within Rigol's specs of better than -30dBc, namely -40dBc.

Anyway, interesting tests that you're doing there, I wish I had an excuse for spending the money on such a generator...

Yes you are correct about my mix-up with dBc  |O
(I mode the correction in the post)

I made so many measurements in the process - part of getting to know how to drive the equipment - that when it came to present the results - it became even more work  :o

I wanted to make a table - but that's not easy...

So decided to do it verbose - by simply stating the results as seen on the screen shots.

After doing the 100MHz , it was easier to simply refer to the screen shots - so those who are interested can interpret their own.

Yeah .. this is a nice bit of kit (as are other RF signal generators I am sure - waiting to get my hands on the Siglent SSG3021x soon

I found some really novel (for me at least) ways to use this device for testing radios and antenna systems

With Radios - its really simple ...

I connect the SG to an antenna (not really legal - but at the power level I use I think it is??) and then set the LEVEL to -110dbm - tune the receiver to the test frequency - and then modulate the SG with a 1KHz sine wave (tone) - now slowly increase the output level - until the receiver 'hears' the tone - it gives a good approximation to the RF sensitivity of the receiver.

Similarly by doing same with and without 'tuned' antenna - you can get approximation of the antenna gain

The great feature of the RF Signal Generators is the external input for modulation - you can use different things here.

Again for testing purposes - I have a stereo encoder and RDS encoder - this can be connected to the modulation input of the SG and we have a well-conditioned FM signal with the 19KHz stereo pilot and RDS pilot - ready to test any FM receiver for sensitivity and signal quality.

With a suitable SDR and GNU Radio - you can generate complex modulation - like DVB-T signals for testing digital TV tuners ...

With RF design and testing the possibilities are endless  ;)

For me the most important aspect of the RF signal generator is to trust its output characteristics.

I am not too bothered with the frequency stability - as I will be using a GPSDO 10MHz reference (picture attached - lots of reviews on youtube on this device) - but having a trusted signal amplitude response is very important as you simply want to 'dial-up' the required LEVEL - without using another instrument in the loop to check if this is indeed correct  :-\

Finally, you are once again correct - the RF SG's are not cheap - they cost more than some SA’s - so you really need to have a good reason for getting one  :P
« Last Edit: July 06, 2020, 09:59:49 pm by noreply »
 

Offline noreply

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Re: Rigol DSG815 - testing feedback and comments
« Reply #4 on: July 09, 2020, 09:26:08 pm »
Testing


Modulation / FM modulation

Some more tests with 1GHz -20dBm with FM modulation at 1Khz and 10Khz

Unfortunately - there appears to be no screen capture possible (or I simply don't know how at this moment in time) on the Rigol DSG815

So I took some .jpg pics to show the settings

Please see the images below
 

Offline noreply

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Re: Rigol DSG815 - testing feedback and comments
« Reply #5 on: July 21, 2020, 02:27:27 am »
I recently acquired a GPSDO (a BG7TBL design)
– its capable of producing a 10MHz reference sine wave signal accurate to 10E-14
– when stabilized over a prolonged period of time
– not moved or touched in any way in an isolated position (because of its high time accuracy
– we can ‘see’ gravitational influence by nearby objects and movement of the device.


For now
– in the few days I have been running it
– it is most likely accurate to at least 10E-12
– but how can you measure this device
– unless you have some reference with even ‘better’ accuracy.


This is the beginning of the ‘time standard or GPSDO and Rubidium’ rabbit hole – BE WARNED!


There is no end – so for now I simply accept that the GPSDO I have is accurate to at least 10E-11



Great!


So what can we do with it?


Well, I have a really good RF signal Generator which I am reviewing – the Rigol DSG815 – it ALSO has an accurate frequency generation mechanism – after all this is VERY important for a RF Signal Generator.


So why not compare the 10MHz signal – a pure sine wave – to the GPSDO’s 10MHz pure sine wave – which we assume is (it most likely is) accurate to 10E-11


So how do we do this – I don’t have a frequency counter – capable of 10E-11 accuracy @ 10MHz – but I do have a MSO5000 capable of plotting x-y for respective CH1 and CH2 inputs.


X-Y plotting on a Oscilloscope – generates interesting Lissajous figures – and if you understand how these are generated – then it’s VERY easy to ‘compare’ any two frequencies to determine how many Hz they are apart – or if indeed they are totally in-synch.


Here is how you do your measurements / testing;-


Connect your oscilloscope’s CH1 to your KNOW (the accurate reference frequency) frequency.


Connect your oscilloscope’s CH2 to the source of the frequency you are trying to measure – the deviation from the KNOWN source.


If you trigger your scope on the CH1 sine wave, you will see a rock steady sine wave (CH1) and a ‘moving’ sine wave on CH2.


The rate – or speed of the CH2 sine wave as it moves out of phase and repeats this continuously – is in essence the time period of the frequency deviation from the CH1 frequency.


Bu simply ‘looking’ at the moving waveform – we cannot tell how much the frequency of CH2 is deviated from the reference Frequency of CH1

BUT

If we now enable X-Y mode – we will see a spinning circle – our Lissajous figure.

The spinning circle represents the phase difference of the two sine waves.
¼ of a ‘spin’ of the circle represents 90 degrees,
½ of a ‘spin’ of the circle represents 180 degrees,
¾ of a ‘spin’ of a circle represents 270 degrees,
1 full ‘spin’ of a circle represents 360 degrees.

Remember because we see the circle in 2 dimensions – when it spins onto itself – it actually has made ½ of a revolution, so it needs to spin onto itself TWO times for a full revolution.

To understand this is very important.

NOW, if we assume that CH1 frequency is rock solid (the time reference) – then any deviation will be in the frequency we are testing – CH2 in our case.

The Rigol DSG815 – was set to be ‘spot-on’ its internal 10.000 000 00 MHz

Its capable of displaying 8 significant digits – this means it can be programmed to produce .01 Hz resolution.

The GPSDO is capable to producing ACCURATE resolution to 10.000 000 00000 MHz


So let’s look at this side-by-side

10.000 000 00
10.000 000 00000

So we can now resolve 0.00001 Hz – that’s incredible for a $100 device!

Back to the ‘spinning circle’ – the rate of the ‘spin’ is an indication of how much deviation in Hz there is between the two frequencies.


So, we nor go to the control panel on the DSG815 – and simply vary the least significant figure – to adjust the output frequency.


As we ‘turn the know’ we are either increasing or decreasing (your choice) the signal generators output frequency – to try to match it as close as possible to the GPSDO reference frequency.


As if you increase the frequency and the circle starts to spin faster – then we are going the wrong way – the sig gen frequency is already too high – we must reduce it.


So if we now reduce the frequency the circle should start to slow down – we keep decreasing the frequency until we can ‘stop’ the spinning circle COMPLETELY.


Unfortunately you will not be able to stop the spin completely – the Rigol DSG815 simply does not have such an accurate clock that it can match the GPSDO.

BUT

We can virtually stop the ‘spin’

You will be able to go down to 0.01Hz increment on the DSG815 and you will find that if you step this ‘up’ by 1 or ‘down’ by 1 this will be your final limit.

When the DSG815 has been ‘warmed-up’ so its internal frequency source becomes stable – you will reach a point where the circle will still spin but VERY slowly – either left or right – depending on the last significant digit you dial.


Now what?



When you reach this stage – get your stop watch out and get ready.


Now we are going to calculate the exact frequency ‘drift’ from the GPSDO reference frequency.


Look at the circle – and wait until it becomes a ‘straight line’ – start your stopwatch.


Wait until the ‘circle’ spins an entire revolution and becomes a ‘line’ again – remember this is only ½ turn because we are viewing in 2D – then wait for another revolution until it becomes a ‘line’ again – now STOP the stopwatch!


VOILÀ!


We have completed the measurements – congratulate yourself if you are still with me  ;)



WARNING – the above ‘stop watch process could take a long time – especially if your signal generator is very close to the 10MHz frequency.



To calculate how much ‘off frequency in Hz’ we are from the reference frequency we do the following;-


In my case with the Rigol DSG815 – it took 172 seconds to make a FULL 360 degree turn of the circle.

If we divide 1 by 172 – we will get the frequency offset

In my case this was 1/172 which is 0.0051813953 Hz

If we round this off to the GPSDO resolution it then becomes;-


0.00581 Hz


Pretty Good frequency accuracy for the Rigol DSG815  :-+


(I am looking forward to performing same test on the Siglent SSG2032X soon)



So what does this mean in relation to the DSG815’s ability to set ‘exact’ frequency?

My offset for the 815 was 0.071 Hz

I could only change the last significant figure

So, can dial either 0.072 – circle still spinning

OR

I can dial 0.070 – circle still spinning – in opposite direction

Because I need to ‘dial’ 0.71581


But since I cannot – because I only have 0.00 Hz resolution and not the required 0.00000 Hz resolution offered by the GPSDO – this is why with the use of the GPSDO reference frequency – I can calculate the ‘exact’ difference needed to have a precise ‘lock’ to the 10MHz.


In my case the Rigol DSG815 was 0.71581 Hz ‘higher’ in frequency than the exact 10.000 000 00 MHz dialed on the control panel.


Interesting that the Rigol DSG800 series specification states a ‘frequency stability’ and not ‘frequency accuracy’

– I don’t think manufacturers like to specify accuracy
– because it can be way off.


See detailed specifications / data sheet on the DSG800 series here

http://telonic.co.uk/v/pdf/rigol/Rigol-DSG800-Signal-Generator-Datasheet.pdf



We just measured – frequency accuracy – something NOT specified in the data – but good to know.



The STABILITY of the frequency – is specified in the data – referenced to 25 deg Celsius


Within the range of 0 to 50 degrees Celsius.


So if the instrument has ‘warmed-up’ and the room temperature where the instrument is operating is within the 0 to 50 degrees Celsius, Rigol specifies that the deviation in frequency will be less than 2ppm



To understand this better

– visually it can be seen as this

Either
 
09.999 999 90
 
OR

10.000 000 10


Remember – Rigol only specifies STABILITY – not accuracy

 
So we determined the accuracy to be within 0.71581 Hz


And the


STABILITY within 0.2 Hz – at least around my room temp which was 21 degrees Celsius.


The frequency did not drift more than 0.00581Hz for over 10 minutes – when instrument was warmed up.



These are certainly impressive figures for a ‘cheap’ (non Agilent or Keysight) instrument.



I did not stress the temperature stability to the entire range from 0 to 50 degrees Celsius unfortunately.



Conclusion


I have demonstrated how a GPSDO is a very useful instrument to have in your laboratory.

With this device and a simple oscilloscope – capable of X-Y plot – we can measure the frequency accuracy of an instrument under test, and consequently its stability with respect to temperature.

The Rigol DGS815 RF Signal Generator proved to be well within its published specifications.


See attached screen captures.

It’s not possible to ‘see’ spinning circle in the screen shots – so I tried to ‘capture’ as it was moving from straight line – to indicate its movement.



Hope the above – rather detailed explanation of this simple testing process is useful for application to other devices under test.


 

Offline noreply

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Re: Rigol DSG815 - testing feedback and comments
« Reply #6 on: August 10, 2020, 11:23:31 pm »
Today I had access to a IRF 2025 (old Marconi Instruments RF Signal Generator) which has exceptional specifications for a 20 year old design device.


Its phase noise which has a specification of -121 dBc/Hz at 1GHz (20KHz offset)


This is considerably better than the only 5 year old design of the DSG815


 – which has a phase noise figure of  -105 dBc/Hz (typ.) at 1GHz (20KHz offset)


So this was a good opportunity to see if the DSG815 did indeed have a better phase noise than the SVA1032X and if the ‘oldie’ IFR2025 was still as good as it was in its specified phase noise figures.


Since the SVA1032X claims to have a -98 dBc/Hz Phase Noise @ 10 kHz offset (1 GHz, Typ.), then it will most likely be the LIMITING instrument when measuring the phase noise.


Remember you cannot measure phase noise of an instrument which has a BETTER phase noise response than the phase noise of the device generating the signal for the phase noise measurement.


Well if you look at the respective plots shown below ;-


SVA1032X phase noise using DSG815 source 0dBm 1GHz (10KHz offset) - 30Khz span


We can see that the SVA1032X does not meet its published phase noise specifications of -98 dBc/Hz @10 kHz offset at 1GHz – or at least my respective device did not match this figure.


SVA phase noise is reported as -87.89dBc/Hz

Of cause – what could cause this specification not being attained - is that the inherent phase noise of the DGS815 could be HIGHER (worse) than the -98dBc/Hz of the SVA


So I did another test


I ran the same test with the IFR2025 and the results are shown in the following plot ;-


SVA1032X phase noise using IFR2025 source 0dBm 1GHz (10KHz offset) - 30Khz span


Here we can see that the SVA phase noise is reported as -89.42dBc/Hz


Since this figure is not same as the DSG815 – in fact its considerably better but NOT close to the SVA specification – this means that BOTH of the RF Signal generators had worse phase noise figures than the SVA at the 10KHz offset of the 1GHz carrier at 0dBm


I wonder why Siglent specified the 10KHz offset in the specifications?


My guess is because  this small offset makes it much harder to attain the phase noise figure – as most Sig Gen will have WORSE figures at this small offset.


So I decided to run some more test plots but this time at 100KHz offset.


This offset  should produce much lower noise figures from the Signal Generators
 
– so now we can see if the figures at this offset (100KHz) will match the specified 98 dBc/Hz @10 kHz offset at 1GHz of the SVA


See plots

SVA1032X phase noise using IFR2025 source 0dBm 1GHz (100Khz offset) - 2mhz span

SVA1032X phase noise using DSG815 source 0dBm 1GHz (100Khz offset) - 2mhz span


The tighter ‘span’ produced better noise figures – I suspect this is the inherent SVA processing – with tighter span there is better resolution.


SVA1032X phase noise using DSG815 source 0dBm 1GHz (100Khz offset) - 0.5mhz span

SVA1032X phase noise using IFR2025 source 0dBm 1GHz (100Khz offset) - 0.5mhz span

Unfortunately BOTH of the Signal Generators - even at the 100KHz offset - could not attain the -98dBc/Hz noise figure - which was specified at a 10KHz offset.


Homework - for someone willing to undertake some testing ...

If you have an exceptional RF Signal Generator with much better noise figures banded about in the above testing

AND

You happen to have a SSA3000X or SVA1032X

- then you could perform a phase noise test at 1GHz carrier with a 10KHz offset
- and see if you get your SSA or SVA report close to or better than the specified -98dBc/Hz noise figure.  :popcorn:



 

Offline rdsi

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Re: Rigol DSG815 - testing feedback and comments
« Reply #7 on: August 11, 2020, 12:49:55 am »
Yeah, I got the DSG821A & have been happy with it so far.  One area I was disappointed with was the internal  IQ generator.  Although I purchased this with intent of using an external IQ source the internal generator is only usable by loading an arb file.  This file can be generated using MathLAB and Rigol Ultra IQ Station in conjunction with Ultra Sigma.

I contacted Rigol about the format of this file so I could perhaps use a spreadsheet to develop my data then convert it to the arb file format,but, they just kept pointing me to their MathLAB solution.  So I tried their solution but there seems to be no support for the 821?

Anyway, when I get dual a arb generator I'll be able to test out the IQ modulation.

I have found some arb file formats for Rigol signal generators but they are just for 1 channel.  The file format for the 821 must somehow encode both the I & Q channels.

If someone has the Rigol MathLAB solution could you post a file so I could decipher the format?

Thanks
 

Offline noreply

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Re: Rigol DSG815 - testing feedback and comments
« Reply #8 on: August 11, 2020, 01:25:36 am »
@rdsi

Thanks for the feedback on the 821A

Yes apparently most (at least the SSG range - Siglent's  offering) IQ enabled Sig Gens need the IQ data to be prepared via an external device.

There is quite a bit of 'crunching' required to generate the IQ data -my guess is that the processors in the devices are not equipped to do this effectively - so unless you have a Keysight or R&S device - its most likely going to have to use a 3rd party source for the data.

It can however be set-up to be seamless if it is well specified and has the correct interface - i.e. use the network connections and load the data automatically.

Not sure if you are aware that there is another much older thread on the DSG800 series

https://www.eevblog.com/forum/testgear/upcoming-rigol-dsg815830/

There are several other forum members who have the 800 series - but not sure if they have the IQ 'A' variant(s)

I had a quick look at the Rigol Ultra IQ Station software some time ago - but don't have the appropriate HW to take if further.

Not sure if you tried - screen shots attached for you to see

Good Luck
 

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Re: Rigol DSG815 - testing feedback and comments
« Reply #9 on: August 11, 2020, 02:43:32 am »
Phase Noise check of SVA1032X using my old tired HP 8654B that drifts like a SOB.  :horse:
Frequency adjustment mechanism is unreliable and sticky so ~474 MHz out of 520 MHz is all I got for you..... more  :horse:
View was needed to catch the below screenshot and even then the fundamental peak had drifted from CF despite the HP's hour long warm up.  ::)

Clues of how to meet the datasheet spec are in the datasheet itself with an image of the settings used.

« Last Edit: August 11, 2020, 03:06:07 am by tautech »
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Offline noreply

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Re: Rigol DSG815 - testing feedback and comments
« Reply #10 on: August 12, 2020, 01:26:54 am »
@tautech

First of all THANK YOU for being the only person (so far) to attempt to do the HOMEWORK  :clap:


However

– despite your effort of doing the work (10/10 for this part)

– I think you failed to fully understand the basics of Phase Noise (PN) and more importantly how PN is actually specified thereby allowing a meaningful measurement to take place.



I found an excellent tutorial on The Signal Path (YouTube) episode TSP #162


The graphics used for this presentation are available here …

https://www.keysight.com/upload/cmc_upload/All/20180720_KEE7_PhaseNoise.pdf


This is a much more in-depth presentation

– probably great to review later

– but for the scope of my post here I have just ‘lifted’ some screenshots based on the above slides from TSP #168 (thank You Shahriar for doing this video).



In short, phase noise MUST be defined for any given instrument as shown in the following slide ;-



what is phase noise - TSP #162  @8.03.JPG



Once defined as a specific ‘offset’ and carrier frequency – when making measurements IT MUST also be measured as the SAME carrier frequency and ‘offset’


For the SVA1032X

– as shown in Siglent’s specifications data for this device – this is


-99 dBc/Hz @10 kHz Offset Phase Noise (1 GHz, Typ.)


So making a PN measurement with a carrier frequency not precisely at 1GHz and an 'offset' frequency not exactly at 10KHz  – IS TOTALLY MEANINGLESS - when comparing this to Siglent's published PN specification.


– It’s like me posting a picture of a NFL football and saying it’s the ‘ball’ used by the UK premier league to play soccer with

– when I really should have posted a picture of a SOCKER ball instead.


(sorry for the football analogy - but ANY similar analogy or a ridiculous comparison would suffice)



When working with PN specifications and measurements


the OFFSET and CW frequencies at which phase noise is measured are CRUCIAL to meaningful measurements, as is also the relative power level of the Carrier.



If you have a look at the following slide ;-



phase noise related to bessel functions - further away from carrier the lower the PN - TSP #162  @11.14.JPG



You will see that the Phase Noise is related to the Bessel functions

– and again, in short,

- the further we move from the carrier frequency – the ‘offset’ – the BETTER the resultant phase noise measurement becomes.



So if Siglent (or anyone else) specifies a phase noise of


-99 dBc/Hz @10 kHz Offset Phase Noise (1 GHz, Typ.)



This means you MUST measure it with an offset of 10KHz and not 948Hz AND at 1GHz Carrier Frequency and not 474 MHz



Because of the shape of the Bessel function

– the closer you are to the Carrier Frequency (the smaller the offset frequency)

– then it becomes far more challengeable to get low PN figures.



Even Keysight and R&S will be challenged to have great PN figures at small ‘offsets’



Now,

lets have a look,

specifically at the Siglent SVA1032X phase noise response



Please have a look at the following slide ;-



SVA1032X phase noise plot from 100Hz to 100MHz - using Signal Hound Low Phase Noise Generator - TSP #162  @34.05.JPG



We can see that it becomes relatively ‘flat’ from about 10KHz to 100KHz


So when, Shahriar Shahramian made the above phase noise measurement of the Siglent SVA using his low phase noise source (the Signal Hound PNCS-1) and the Agilent 26GHz SSA which has a ‘built-in’ phase noise function, he mistakenly specified his noise marker at 100KHz, whereas it should have been specified at 10KHz.


BUT


Because the phase noise response in that region (from 10KHz to 100KHz) is ‘flat’ the resultant noise figure is pretty close to what it would read at the correct 10KHz offset frequency.




I hope the above theory and slides from Keysight’s Bob Nelson and Shahriar’s great video are sufficient to clarify how proper PN measurements should be made.



So for the actual measurement data part of your HOMEWORK

– you score 0/10

– because you TOTALLY failed to see the significance of how PN is defined and more importantly how it should be measured  :palm:





As a bonus – for Siglent SVA


I once again decided to make some PN measurements using the DSG815 as the source of my PN measurements.

The DSG815 is specified to have a ‘better’ PN than the SVA – so should not ‘limit’ the measurement.



See plots below


SVA1032X phase noise using DSG815 source 0dBm 1GHz (10KHz offset) - 100Hz RBW - 30Hz VBW .png



SVA1032X phase noise using DSG815 source 0dBm 1GHz (10KHz offset) - 1Hz RBW - 30Hz VBW .png



Here we can see different PN measurement RESULTS based on different RBW and VBW values ONLY


OK you would think that ‘tighter’ RBW and VBW will give more ‘tuned’ result – but in fact it reports a worse PN figure.


What is important is to know precisely what RBW and VBW figures for the respective measurement should be used



I repeated the same measurement

– but used different RBW and VBW figures

– both set at 1KHz with a span of 250KHz


Using these values

– the PN of the SVA was very close to the specified PN by Siglent.



PLEASE NOTE

I repeated the measurement at Both 10KHz and 100KHz offsets


SVA1032X phase noise using DSG815 source 0dBm 1GHz (10KHz offset) - 1KHz RBW - 1KHz VBW .png

SVA1032X phase noise using DSG815 source 0dBm 1GHz (100KHz offset) - 1KHz RBW - 1KHz VBW .png


– because the SVA phase Noise response is fairly linear in this range

– as demonstrated by Shahriar’s plot and shown in this


SVA1032X phase noise plot from 100Hz to 100MHz - using Signal Hound Low Phase Noise Generator - TSP #162  @34.05.JPG


Plot



In fact Siglent somehow managed to ‘dip’ the PN response precisely at the 10KHz offset – resulting in a measured response of -100dBc/Hz   :clap:




@tautech,

I want you to know that about 2 weeks ago - I was a TOTAL noob - and thought I was making meaningful PN measurements myself when posting my analysis plots  :palm:

But sadly I was not  |O

It was not until studying and trying to understand the concepts of PN and how its defined together with how to make meaningful measurements (thank you Shahriar and Bob Nelson) that I can finally feel confident in making PN measurements.

I am sure that MANY others on this forum will fall fowl at mastering PN measurements.

I hope this short overview will help those who do  :)


.. BTW

Please be rest assured that the

SVA passes Siglent's published Specifications for the PN  :-+
 

Online tautech

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Re: Rigol DSG815 - testing feedback and comments
« Reply #11 on: August 12, 2020, 02:15:56 am »
And another I prepared yesterday half expecting some rejection of the ~500 MHz screenshot so to satisfy SVA/SSA myself will indeed meet its spec.
SSG3021X @ 1 GHz 0 dB which as you probably know has specified PN: -110 dBc/Hz @1 GHz ,offset 20 kHz (typ.)

So again, SVA/SSA PN will limit results.

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Offline rdsi

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Re: Rigol DSG815 - testing feedback and comments
« Reply #12 on: August 12, 2020, 03:40:10 am »
OK, I finally figure out how to get IQ station installed and managed to produce a file.  I have yet to figure out how to transfer data via LAN to the instrument but was able to use a USB drive.  The file loaded & I was able to produce some modulation with the internal generator - see below.

So it's going to take some messing around to see how useful this is compared to an external modulation source.  Unknown to me IQ station does include tools to load raw data files such as produced by a spreadsheet.  So this is a plus.

However, my initial feel for the RIGOL software is that it's pretty low quality.   On my computer many of the screen functions are partly obscured  so you're left to extrapolate their meaning and the color coding makes it difficult to discern clickable objects.  Perhaps that's why the program title includes (Trial) in it?

Anyway, I feel a little more hopeful that the internal IQ generator maybe useful after all.

Having gotten time using the machine in this exercise I really noticed with the overhead lights on both the MOD & RF button LED's are useless.  So unless your in the home screen where their status is shown you'll need to cup your hand over them to see if they're on or off!
 

Offline noreply

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Re: Rigol DSG815 - testing feedback and comments
« Reply #13 on: August 12, 2020, 12:02:31 pm »
And another I prepared yesterday half expecting some rejection of the ~500 MHz screenshot so to satisfy SVA/SSA myself will indeed meet its spec.
SSG3021X @ 1 GHz 0 dB which as you probably know has specified PN: -110 dBc/Hz @1 GHz ,offset 20 kHz (typ.)

Well done - we now have yet another who understands PN specifications and can make a meaningful measurement  :clap:

One question that you could investigate ...

Please do EXACTLY SAME analysis - but this time change the RBW and VBW to 1Hz - and see what happens?

It would be nice to know what should be the 'best' settings for RBW and VBW to produce the most accurate result?
 

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Re: Rigol DSG815 - testing feedback and comments
« Reply #14 on: August 12, 2020, 07:07:02 pm »
When I first got my DSG821A (last week) I checked out all the basics & found them to be within the data sheet specs.  Although I planned to operate my unit using a GPSDO I did checkout the internal OSC because the data sheet spec indicated it was pretty darn good.

After about an 1 1/2 hours the OSC stabilized from cold 9,999,999.6xx to 9,999,999.890 well within the 2 ppm specs.

Over the next hour I collected the following statistics using my GPSDO based counter:
 

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Re: Rigol DSG815 - testing feedback and comments
« Reply #15 on: August 12, 2020, 08:30:02 pm »
@rdsi

Yeah ... considering that the standard unit does not come with the OCXO - but just a TCOX - its out-of-the-box frequency accuracy is pretty good.

In fact my Rigol DSG815 was 0.71581 Hz ‘higher’ in frequency than the exact 10.000 000 00 MHz dialed on the control panel.

If you have a GPSDO - use procedure posted above - with the use of an Oscilloscope with X-Y mode - you can get much higher precision measurement  than your VERY NICE counter (I think?)  ;)

Provided your room temperature where the DSG resides stays constant - the 'drift' is well within specifications.
 

Offline rf-loop

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Re: Rigol DSG815 - testing feedback and comments
« Reply #16 on: Yesterday at 01:30:43 am »


Harmonics

CW mode
For Frequency range of 1 MHz ≤ f ≤ 3.6 GHz
At an Amplitude level of ≤ +13 dBm
The Harmonics should be < -30 dBc



My Test Findings

Using a direct connection from DSG815 to SVA1032x with > 6GHZ low loss cable

At 100MHz , 20dBm Amplitude (DSG815)
(this is OUTSIDE PUBLISHED SPECIFICATIONS which are limited to <13dBm)

SVA1032x Resultant measurements are
Frequency = 100MHz
Within Specifications (spot-on)

Amplitude = 19.63dBm
Specification states typical < 0.5dBm error
Conclusion DSG815 well within Specifications

Harmonics
1st Harmonic -20.14dBm
This is outside the specifications of < 30dBm
BUT keep in mind we are operating at 20dBm Amplitude setting
which is outside the < 13dBm Specification


At 100MHz , 13dBm Amplitude (See 13dbm.png)
SVA1032x Resultant measurements are
Frequency = 100MHz
Within Specifications (spot-on)

Amplitude = 12.66dBm
Deviation was -0.34dBm
Specification states typical < 0.5dBm error
Conclusion DSG815 well within Specifications

Harmonics
1st Harmonic -34.13dBm
This is inside the specifications of < 30dBc

At 100MHz , 0dBm Amplitude (See 0dbm.png)
SVA1032x Resultant measurements are
Frequency = 100MHz
Within Specifications (spot-on)

Amplitude = -0.27dBm
Deviation was -0.27dBm
Specification states typical < 0.5dBm error
Conclusion DSG815 well within Specifications

Harmonics
1st Harmonic -47.08dBm
This is inside the specifications of < 30dBc



At 100MHz , -10dBm Amplitude (See -10dbm.png)
SVA1032x Resultant measurements are
Frequency = 100MHz
Within Specifications (spot-on)

Amplitude = -10.35dBm
Deviation was -0.35dBm
Specification states typical < 0.5dBm error
Conclusion DSG815 well within Specifications

Harmonics
1st Harmonic -52.94dBm
This is well inside the specifications of < 30dBc


At 100MHz , -20dBm Amplitude (See -20dbm.png)
SVA1032x Resultant measurements are
Frequency = 100MHz
Within Specifications (spot-on)

Amplitude = -20.31dBm
Deviation was -0.31dBm
Specification states typical < 0.5dBm error
Conclusion DSG815 well within Specifications

Harmonics
1st Harmonic -53.19dBm
This is inside the specifications of < 30dBc



At 100MHz , -110dBm Amplitude (See -110dbm.png)
SVA1032x Resultant measurements are
Frequency = 100MHz
Within Specifications (spot-on)

Amplitude = -110.56dBm
Deviation was -0.56dBm
Specification states typical < 0.5dBm error but can be <0.9dBm
Conclusion DSG815 well within Specifications

Harmonics
1st Harmonicit’s below the noise floor of the SVA at -142.79dBm
A tribute to the Siglent SVS1032x – and its low noise floor of -142dBm well done!
This is inside the specifications of < 30dBc

OK , without going through ALL of the individual results here is summary for other frequencies …

10dbm at 500Mhz (see 500mhz @ 10dbm.png)
Frequency 500.2666667MHz
Deviation is 2.66KHz – acceptable limit is 1KHz (I strongly suspect the SVA in error here because of the LARGE frequency span in measurement)
Amplitude = 9.65dbm – well within spec
1st Harmonic = -31.25dbm – well within spec


0dbm at 500MHz (see 500mhz @ 0dbm.png)
Frequency 499.536667MHz
Deviation is 4.633kHz – acceptable limit is 1KHz (I strongly suspect the SVA in error here because of the LARGE frequency span in measurement)
Amplitude = -0.31dbm – well within spec
1st Harmonic = -40.86dbm – well within spec


-110dbm at 500MHz (see 500mhz @ -110dbm.png)
Frequency 500MHz
Deviation is 0kHz – acceptable limit is 1KHz
Amplitude = -110.64dbm – well within spec
1st Harmonic – it’s below the measured noise floor of the SVA at -135.36dBm


Nitpick or not  ;) but...
One sidenote because when we talk physics I like we keep basic simple fundamentals right, as example how we name basic fundamental things -  like example harmonics.
Looks like this is not normal typemistake because it is repeated several times.
Forum have full of readers with different level of knowledge etc. So it is perhaps good to try keep basics somehow right.
Here is lot of total noobs what may learn wrong things what are then later difficult to reverse learn away and swap with right.

1st harmonic == fundamental frequency! I believe you are talking about 2nd harmonics.
It is nice if you have time for correct these in this quoted OP.

Normally we set generator for some frequency, example tune it for produce 100 MHz  sinewave.
What are harmonics.  1st harmonic is 100 MHz!  2nd harmonic is 200 MHz, 3rd is 300MHz etc. Harmonic number is like multiplier.
If you find some other information in www or irl they are just perfectly wrong (this mistake is not at all rare).

But overall nice test, more these...  with good accurate info how tests are made as here is...
« Last Edit: Yesterday at 01:37:42 am by rf-loop »
If practice and theory is not equal it tells that used application of theory is wrong or the theory itself is wrong.
-
Harmony OS
 
The following users thanked this post: tautech

Online tautech

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Re: Rigol DSG815 - testing feedback and comments
« Reply #17 on: Yesterday at 01:57:38 am »
Nitpick or not  ;) but...
One sidenote because when we talk physics I like we keep basic simple fundamentals right, as example how we name basic fundamental things -  like example harmonics.
Looks like this is not normal typemistake because it is repeated several times.
Forum have full of readers with different level of knowledge etc. So it is perhaps good to try keep basics somehow right.
Here is lot of total noobs what may learn wrong things what are then later difficult to reverse learn away and swap with right.

1st harmonic == fundamental frequency! I believe you are talking about 2nd harmonics.
It is nice if you have time for correct these in this quoted OP.

Normally we set generator for some frequency, example tune it for produce 100 MHz  sinewave.
What are harmonics.  1st harmonic is 100 MHz!  2nd harmonic is 200 MHz, 3rd is 300MHz etc. Harmonic number is like multiplier.
If you find some other information in www or irl they are just perfectly wrong (this mistake is not at all rare).
Thank you.

Like others I had harmonics understanding wrong also as I found out based even on a Wikipedia link:   ::)
https://en.wikipedia.org/wiki/Harmonic
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Offline noreply

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Re: Rigol DSG815 - testing feedback and comments
« Reply #18 on: Yesterday at 09:31:52 am »
@rf-loop , @tautech

Thank you for pointing out this misleading interpretation by myself.

I guess my professor who was teaching me (many years ago) the fundamentals of signals & networks (not computer networks – but signal processing RF networks) did not have the convenience of Wikipedia that he could refer his student to.

We were taught 1st principal theories  - so that once you understand the theory – you can always derive subsequent solutions.

With sinusoid frequencies, when you have a fundamental frequency – it was considered ‘the fundamental frequency’ – subsequent harmonics (and the math says there will be harmonics) should start as 2nd, 3rd, 4th, etc, etc. where the fundamental frequency is the 1st in this progression.

This sounds counterintuitive – because why would the fundamental frequency be called a harmonic?

Unfortunately, it’s because of the math and the need to number a progression – so the fundamental is also the 1st harmonic.


Nit-picking or not , from a definition point of view – you make a valid point  :-+

However I am also sure that most forum members would realize that the 1st harmonic (which is the fundamental frequency) cannot exhibit the SAME amplitude unless its the fundamental frequency.

So in the context of the measurements above – it is by observation (not necessarily definition – which is wrong) that most people would realize that the 1st harmonic is really the 2nd harmonic – by definition.


This however does not justify the incorrect use of the nomenclature.


Thank you for bringing this to MY attention – and most likely to may others :clap:



OP corrected
 


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