Author Topic: Looking for a dynamic signal analyzer with extended bandwidth  (Read 1143 times)

0 Members and 1 Guest are viewing this topic.

Offline _Wim_

  • Frequent Contributor
  • **
  • Posts: 423
  • Country: be
Looking for a dynamic signal analyzer with extended bandwidth
« on: October 21, 2017, 08:38:43 PM »
I am looking for a “dynamic signal analyzer” with extended bandwidth (“DC” to approx. 10MHz). This will be used during experimentation with analog front ends for optical sensors (mainly interested in noise and FFT of the modulated light).  Signals of interest are typically small (1mV <>100mV), but sometimes also riding on “large” DC (+-15V). I would like to have input ranges that go down to around -40dBVrms (10mV), and still have a good noise floor (-80dbFs preferred). Input impedance 1M to prevent loading of the DUT.  Budget is around 1500€ but stretchable . I prefer more modern instruments, but off course considering my budget, I will need to make compromises somewhere...

This is my list of possible options I found so far:

1) Dynamic signal analyzer + spectrum analyzer
Most (affordable) spectrum analyzers start only somewhere around 9 KHz.  I could use one of these combined with an older dynamic signal analyzer like an HP 35665A, but these are huge, quite old and go still for quite some money. Also it is annoying to have to use 2 unit for the range I am interested in. Most spectrum analyzers will need some kind of active probe for the higher input impedance required (could be something homebrew because it only needs to go up to 10MHz). Not the most practical solution. I already have a CMU200, so the additional range offered by the spectrum analyzer is of no real interest.

2) USB  Spectrum Analyzer:
Signal Hound sa44b covers” the range I am interested in as it goes from 1 Hz to 4.4GHz, I am however unsure if no compromises were are made at the low end to go up this high. The datasheet does not specify a lot. Needs the (homebrew) active probe and a DC block. Unsure about the performance for my goals.

3) High Resolution Scope
An alternative could be the picoscope 4262 . This one is a little low on bandwidth, but so far seems like a reasonable solution.  It does seem quite expensive for what it only offers.  If bandwidth would be a little higher, this was a winner. The picoscope 5000 series also claim 16 bit of resolution, but their noise specs are much worse.

4) HP 89410-89441A  (with or without RF-downconverter)
This seems like a good solution for what I need. Disadvantages are they are very big and heavy, which makes importing them from the US  to Belgium very expensive . In Europe they do not seem to be common, and if they appear on Ebay, they are way overpriced.  They are typically quite old (1994-98), and there seems to be a common problem with the corners of the screen getting quite dim (there is a VGA port available however). Temped by this solution also as it also offers network analyzer capabilities if the second channel is installed.

Any advice, tips, other units to consider?

Edit: added hyperlinks to specification datasheets
« Last Edit: October 21, 2017, 09:20:20 PM by _Wim_ »
 

Offline _Wim_

  • Frequent Contributor
  • **
  • Posts: 423
  • Country: be
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #1 on: October 21, 2017, 08:56:33 PM »
Maybe also a quick question. Many spectrum analyzer specify DANL in dBm/Hz. If the spectrum analyzer has a RBW of 0.1Hz, can you subtract 20dbm additional from the specified specs (eg, in the case of the signalhoud, DANL at 10Hz is specified as -124dBm/hz, but as this unit has a possible RBW of 0.1 Hz, noise at 10Hz would be -144dBm, correct?)

 

Offline nctnico

  • Super Contributor
  • ***
  • Posts: 12765
  • Country: nl
    • NCT Developments
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #2 on: October 21, 2017, 09:23:05 PM »
Maybe you can get an Anritsu MS4630B for that budget. That is a network analyser from 10Hz to 300MHz and it does have 1M Ohm inputs.

Another option would be the GW Instek MDO2000E series:
http://www.gwinstek.com/en-global/products/Oscilloscopes/Digital_Storage_Oscilloscopes/MDO-2000E_Series
If the sensitivity is too low you could use an external amplifier. The advantage of using an FFT based oscilloscope is that you get the spectrum from one acquisition instead of a scan during a period of time. The MDO-2000E also has input filtering you can play a bit with the effects of filtering on your signal. I have used my GW Instek GDS2204E (which only has standard FFT) for a similar purpose; look at signals coming from a sensor to see what kind of noise is there and what kind of filtering/signal conditioning works well. I kinda bought it specifically for that project.
« Last Edit: October 21, 2017, 09:24:56 PM by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
The following users thanked this post: _Wim_

Offline _Wim_

  • Frequent Contributor
  • **
  • Posts: 423
  • Country: be
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #3 on: October 21, 2017, 09:31:59 PM »
Thanks for your reply. The Anritsu does look like an interesting device. Do you want to sell yours? I willing to pay the double of what you paid  ;D

The MDO2000E still remains an 8-bit device. As I am interested in looking at my signal together with the noise at the same time,so I need a bigger dynamic range then the 8-bit can offer, and pre-amp does not help for this.
 

Offline nctnico

  • Super Contributor
  • ***
  • Posts: 12765
  • Country: nl
    • NCT Developments
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #4 on: October 21, 2017, 09:54:31 PM »
I think I want to hang on to my MS4630B for a bit longer.
Another option might be the 'analog discovery 2'. It ticks all your boxes but I don't know if the software works for your purpose.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
The following users thanked this post: _Wim_

Offline _Wim_

  • Frequent Contributor
  • **
  • Posts: 423
  • Country: be
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #5 on: October 21, 2017, 10:30:25 PM »
Another option might be the 'analog discovery 2'. It ticks all your boxes but I don't know if the software works for your purpose.

This looks indeed like a possible candidate, although a bit toy-like. It will need a low noise pre-amp for sure, as the low input ranges use "digital zoom", resulting in a max resolution of 0.32mV on the input range of 0.5mV/div  :palm:, which is off course way too low for my needs. But still, for the price, it seems quite a versatile device.

No clear specs for the noise performance of the entire system however, and if I see the specs of the the ADC and buffers, I think it will not be so fantastic. But maybe worth a play around with...
« Last Edit: October 21, 2017, 10:33:24 PM by _Wim_ »
 

Offline _Wim_

  • Frequent Contributor
  • **
  • Posts: 423
  • Country: be
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #6 on: October 21, 2017, 10:50:34 PM »
For future reference for others: here is the manual for the Anritsu MS4630B (specs in section 1.5)

@nctnico, do I reed this correct that this unit has only 2 input ranges,one of 0dBm and one of 20dBm? For measuring small signals a pre-amp would still be necesarry (not really an issue, but worth mentioning).
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 5318
  • Country: us
  • DavidH
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #7 on: October 22, 2017, 02:45:03 AM »
Something from Cleverscope might be suitable.
 
The following users thanked this post: _Wim_

Offline egonotto

  • Regular Contributor
  • *
  • Posts: 109
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #8 on: October 22, 2017, 05:52:32 AM »
Hello,

possibly a picoscope 5000 can do it.

The pictures are with 20MHz limit.
The first 3 are with input from the signalgenerator with 1MHz sine and an attenuator.
The last 2 are with an 50 Ohm termination to show the noise level.

If you have questions feel free to ask (too for picoscope 4262 and analog discovery).


Best regards
egonotto


 
The following users thanked this post: _Wim_

Offline _Wim_

  • Frequent Contributor
  • **
  • Posts: 423
  • Country: be
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #9 on: October 22, 2017, 06:28:15 AM »
Hello,

possibly a picoscope 5000 can do it.

The pictures are with 20MHz limit.
The first 3 are with input from the signalgenerator with 1MHz sine and an attenuator.
The last 2 are with an 50 Ohm termination to show the noise level.

If you have questions feel free to ask (too for picoscope 4262 and analog discovery).


Best regards
egonotto

Thanks for the screenshot. The 5000 series indeed perform a bit better than I expected. They still need a preamp however. If you look at the plot with the 50 ohm termination, there is still around 40µV of noise and some DC offset (not a real problem if it is stable). The noise is better then the spec (100µV for 12 Bit, 70µV for 16 bit) , but when measuring signals of a couple of mV, this is still too high. The 4262 spec is around 8µV for 16 bit, which means it is at least 10 times better noise wise (all other specs are however worse however).

 

Offline _Wim_

  • Frequent Contributor
  • **
  • Posts: 423
  • Country: be
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #10 on: October 22, 2017, 06:29:19 AM »
Something from Cleverscope might be suitable.

Thanks, I will have a good look at their specs. Haven't come across one of these before.

Edit: just checked, no real noise specifications for these. Typiccally that means they are not fenomenal. Do you use one of these?
« Last Edit: October 22, 2017, 06:41:15 AM by _Wim_ »
 

Offline egonotto

  • Regular Contributor
  • *
  • Posts: 109
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #11 on: October 22, 2017, 07:14:55 AM »
Hello,

as the picoscope 5000 have 500MS/s (12bit) you can use more bit.

With 14 bit you have 31.25 MS/s if i understand it right (one channel).
Than you get lower noise in time view.
The noise in 10mV is not much lower than the noise in 50mV so the pictures are with 50mV.

You can zero the DC offset. I measure the drift and post the result later.

Yes the 4246 is better and the DC-drift is better.

Best regards
egonotto



 

Offline _Wim_

  • Frequent Contributor
  • **
  • Posts: 423
  • Country: be
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #12 on: October 22, 2017, 07:33:13 AM »
Hello,

as the picoscope 5000 have 500MS/s (12bit) you can use more bit.

With 14 bit you have 31.25 MS/s if i understand it right (one channel).
Than you get lower noise in time view.
The noise in 10mV is not much lower than the noise in 50mV so the pictures are with 50mV.

You can zero the DC offset. I measure the drift and post the result later.

Yes the 4246 is better and the DC-drift is better.

Best regards
egonotto

Thanks for these last pictures, very informative. The 5000 series perform way better then spec! 12µV RMS noise is indeed comparable to the 4262. I do not understand were the 70µV rms comes from in the spec for the 5000 series?


Edit: removed my confusion
« Last Edit: October 22, 2017, 07:58:46 AM by _Wim_ »
 

Offline hagster

  • Regular Contributor
  • *
  • Posts: 122
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #13 on: October 22, 2017, 07:58:04 AM »
How about an Airspy HF+?

http://airspy.com/airspy-hf-plus/

Should be availiable soon and has 18bit dynamic range and DC to 30mhz coverage.


https://www.rtl-sdr.com/airspy-hf-upcoming-low-cost-yet-high-performance-hf-sdr/
 

Offline egonotto

  • Regular Contributor
  • *
  • Posts: 109
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #14 on: October 22, 2017, 08:14:03 AM »
Hello,

it is the min and max value for the 10 traces.

I don't know how picoscope 6 make the measure exakt.
Use they all samples or only a subset?
To update the screen fast, they take only a subset of the samples to show the trace.

I think my 4262 is in spec.

In the datasheet they say it is 8.5uV RMS in 10mV range.
My 4262 has in 10mV range near 8.5mV RMS noise.
And the noise spec from Pico Technology are only typical value.

When I remember right, say write me, that they tolerate 20%.

This measure is with a 50Ohm termination with a metal cap.
Without termination the noise is far bigger.

The peak-peak measures on my picoscopes are about 10 times greater than the RMS measures (most people say that peak-peak values are about 6 times greater than the RMS value)

The DC drift on the 4234A is about 100uV and on the 4262 about 25uV after 40 minutes

I can save a trace and than we can look was is real.


Best regards
egonotto

 
The following users thanked this post: _Wim_

Offline _Wim_

  • Frequent Contributor
  • **
  • Posts: 423
  • Country: be
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #15 on: October 22, 2017, 08:17:43 AM »
How about an Airspy HF+?

http://airspy.com/airspy-hf-plus/

Should be availiable soon and has 18bit dynamic range and DC to 30mhz coverage.


https://www.rtl-sdr.com/airspy-hf-upcoming-low-cost-yet-high-performance-hf-sdr/

I find it hard to correlate these specs to what I want to do. The 18bit refers to the DDC (digital down converter), but I am unsure how this relates to the dynamic range. I have also no idea how to interpreted the minimum detectable signal specs (MDS). I can image this device being able to tune to a very narrow band, and by doing that, achieve a very low noise. But I do not see any specs about scan speed of the spectrum, so I am not sure if you can use these as a normal spectrum analyzer. I need to read a bit how these SDR devices work...
 

Offline _Wim_

  • Frequent Contributor
  • **
  • Posts: 423
  • Country: be
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #16 on: October 22, 2017, 08:22:40 AM »
Thanks for this, I already figured it out and updated my post. The 5000 series start to look nicer and nicer. I used a picoscope before (parallel port device, ADC-212 if I remember correctly) and really liked it. Software was very intuitive and worked flawlessly. I was just a bit thrown off by their 70µV RMS noise spec for the 16 bit mode.

 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 5318
  • Country: us
  • DavidH
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #17 on: October 22, 2017, 08:47:10 AM »
Something from Cleverscope might be suitable.

Thanks, I will have a good look at their specs. Haven't come across one of these before.

Edit: just checked, no real noise specifications for these.  Typically that means they are not phenomenal. Do you use one of these?

Cleverscope was brought to my attention a couple months ago when I expressed a similar interest in low frequency network analysis but I do not have one and I have not directly evaluated one yet.

As far as noise, oscilloscope 1 megohm inputs are all pretty poor in this regard compared to low impedance and audio inputs and they also suffer from high flicker noise; this is just because they use high frequency JFET or MOSFET followers to allow a high impedance input.

So 80dB below 10mVrms over a 10 MHz bandwidth is not going to happen; 40dB would be more realistic.  However if you are using a long FFT to measure noise over a 1 Hz bandwidth, better than 80dB under the same conditions should be easy to achieve.  This is the standard "noise marker" measurement made by good spectrum analyzers; the problem is finding an oscilloscope which supports it.

I was checking the Cleverscope documentation after I wrote the above and they give lots of design and performance details including noise performance here:

https://www.cleverscope.com/files/Cleverscope%20CS328A%20performance.pdf

However I was not able to figure out from their documentation if they can produce an FFT with calibrated equivalent noise bandwidth.  I did not see anything in the Picotech documentation about this ether.
 
The following users thanked this post: _Wim_

Offline egonotto

  • Regular Contributor
  • *
  • Posts: 109
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #18 on: October 22, 2017, 08:47:33 AM »
Hello

_Wim_ wrote:

"Thanks for these last pictures, very informative. The 5000 series perform way better then spec! 12µV RMS noise is indeed comparable to the 4262. I do not understand were the 70µV rms comes from in the spec for the 5000 series?"

Unfortunately my 5243A is worse in noise as the spec tells.
I had a forum with people from Pico Technology.
"https://www.picotech.com/support/post49411.html#p49411"
and with email.

But the spec tells the typical noise only without band width limiting and without average.
With band width limiting and with average you can get much lower noise.

In the picture (picoscope 4262) is the band width 200kHz and the most average (256 sample average (20bit)). Consider is only 40uV/div.


Best regards
egonotto



 

Online KE5FX

  • Frequent Contributor
  • **
  • Posts: 653
  • Country: us
    • KE5FX.COM
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #19 on: October 22, 2017, 08:54:14 AM »
Thanks for this, I already figured it out and updated my post. The 5000 series start to look nicer and nicer. I used a picoscope before (parallel port device, ADC-212 if I remember correctly) and really liked it. Software was very intuitive and worked flawlessly. I was just a bit thrown off by their 70µV RMS noise spec for the 16 bit mode.

If you really need to go down to near DC, the white noise specification might not be enough for your needs.  Most ADCs have some excess 1/f noise below a kHz or so, and DC offset also comes into play since it can leak into the displayed spectrum if not removed by a (very laggy) HPF. 

A few parts, e.g. AD9253, are starting to offer a chopping feature to move the DC offset and 1/f noise to Nyquist, but I wouldn't expect this to be common in general-purpose scopes yet. 

Might not be a big deal, just something to keep in mind.
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 5318
  • Country: us
  • DavidH
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #20 on: October 22, 2017, 09:06:07 AM »
If you really need to go down to near DC, the white noise specification might not be enough for your needs.  Most ADCs have some excess 1/f noise below a kHz or so, and DC offset also comes into play since it can leak into the displayed spectrum if not removed by a (very laggy) HPF. 

A few parts, e.g. AD9253, are starting to offer a chopping feature to move the DC offset and 1/f noise to Nyquist, but I wouldn't expect this to be common in general-purpose scopes yet. 

It is actually much worse than that.  A wide bandwidth (200 MHz) CMOS operational amplifier used for the high impedance input buffer might have a 5nV/sqrHz white noise specification but a 10 MHz corner frequency yielding 1000nV/sqrHz of noise at 10 Hz.  Discrete designs even from 40 years ago are *much* better than this.
 

Offline precaud

  • Contributor
  • Posts: 29
  • Country: us
    • LinearZ
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #21 on: October 22, 2017, 09:21:57 AM »
If an MS4630B will work, you might also consider an Anritsu MS420K or B. 10Hz-30MHz VNA with spec an functionality. Older (90's-90's) unit but well built and quite serviceable. I like mine very much. They were the darling of the telecom industry prior to DSL, so there are quite few of them out there.
 

Offline _Wim_

  • Frequent Contributor
  • **
  • Posts: 423
  • Country: be
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #22 on: October 22, 2017, 05:47:29 PM »
If an MS4630B will work, you might also consider an Anritsu MS420K or B. 10Hz-30MHz VNA with spec an functionality. Older (90's-90's) unit but well built and quite serviceable. I like mine very much. They were the darling of the telecom industry prior to DSL, so there are quite few of them out there.

I will have a look at these also. These older more purpose designed units for sure also have their advantages, but so has a small picoscope with many modern features and warranty.

2 years ago I repaired and HP4276A LCR meter (older unit), but since it has broken down twice. As I mainly experiment in my limited spare time, it can be frustrating having to repair my test gear first, hence I am a bit reluctant for the older gear.

I do like to buy broken gear on Ebay for cheap , and then repair them. But once repaired, they should keep working forever!  :) ?
 

Offline _Wim_

  • Frequent Contributor
  • **
  • Posts: 423
  • Country: be
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #23 on: October 22, 2017, 05:52:16 PM »
If you really need to go down to near DC, the white noise specification might not be enough for your needs.  Most ADCs have some excess 1/f noise below a kHz or so, and DC offset also comes into play since it can leak into the displayed spectrum if not removed by a (very laggy) HPF. 

A few parts, e.g. AD9253, are starting to offer a chopping feature to move the DC offset and 1/f noise to Nyquist, but I wouldn't expect this to be common in general-purpose scopes yet. 

It is actually much worse than that.  A wide bandwidth (200 MHz) CMOS operational amplifier used for the high impedance input buffer might have a 5nV/sqrHz white noise specification but a 10 MHz corner frequency yielding 1000nV/sqrHz of noise at 10 Hz.  Discrete designs even from 40 years ago are *much* better than this.

Unfortunately, these kind of details are typically not published for the scopes (and other gear).

To answer the question of low frequencies, yes, I need them. Light sources used for testing are typically modulated with frequencies between 300Hz an 20Khz, so this range is very interesting for me. My initial thought was to just by a dynamic signal analyzer, but there just so limiting in higher frequencies. Still, noise wise, they are probably still by far the best for my application...
 

Offline hagster

  • Regular Contributor
  • *
  • Posts: 122
Re: Looking for a dynamic signal analyzer with extended bandwidth
« Reply #24 on: October 22, 2017, 05:55:55 PM »
I think you are right regarding the Airspy. It seems to work differently to many SDRs that I am used to. Most capture the entire bandwidth directly.

There are others such as the Perseus SDR that works as a 10khz to 40Mz real time spectrum analyser. You do have to add an external matching pad to increase the impedence of the 50ohm input, but thats not hard to build.

How about an Airspy HF+?

http://airspy.com/airspy-hf-plus/

Should be availiable soon and has 18bit dynamic range and DC to 30mhz coverage.


https://www.rtl-sdr.com/airspy-hf-upcoming-low-cost-yet-high-performance-hf-sdr/

I find it hard to correlate these specs to what I want to do. The 18bit refers to the DDC (digital down converter), but I am unsure how this relates to the dynamic range. I have also no idea how to interpreted the minimum detectable signal specs (MDS). I can image this device being able to tune to a very narrow band, and by doing that, achieve a very low noise. But I do not see any specs about scan speed of the spectrum, so I am not sure if you can use these as a normal spectrum analyzer. I need to read a bit how these SDR devices work...
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf