Author Topic: Bode plot up to a few 100 MHz  (Read 7081 times)

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Offline MartinnTopic starter

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Bode plot up to a few 100 MHz
« on: October 03, 2023, 11:43:13 am »
For characterizing amplifiers (for example an oscilloscope or DAQ frontend) I want to measure their frequency response. Mostly gain, but knowing the phase can't hurt. My RTB2004 does this nicely, unfortunately only up to 25 MHz.
What options would there be for BW up to say 100...300 MHz (I am not a RF guy, so antenna preamps and matching is not relevant for me).

I have used a VNWA for this https://www.sdr-kits.net/introducing-DG8SAQ-VNWA3 , but the installation is somewhat quirky. Very powerful instrument though.
Probably other USB VNAs would also do. With NanoVNA output amplitude does not seem to be adjustable, which makes amplifier measurement quite uncomfortable (needs fiddling with attenuator kit).
LibreVNA https://eleshop.eu/librevna-2-ports-full-vna-100khz-6ghz.html looks interesting.

I don't want to invest in a proper bench top VNA as I neither have the need for a multi-GHz unit nor the bench space.
DIY via SCPI controlled RF gen and scope would be feasible, but a lot of work I'd like to avoid. Also a proper RF generator (sine output and wide range attenuator) would set me back $2000 on top.

Any ideas? Thanks!
 

Offline RoGeorge

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Re: Bode plot up to a few 100 MHz
« Reply #1 on: October 03, 2023, 12:40:17 pm »
I've seen on ebay second hand portable VNA/SA (often used by service man for cellular towers/antennas).  The instruments were in working and sold for less than $500, with a calibration kit and some cables included.  A DIY would probably cost about the same and be less reliable.

Offline 2N3055

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Re: Bode plot up to a few 100 MHz
« Reply #2 on: October 03, 2023, 01:09:50 pm »
For characterizing amplifiers (for example an oscilloscope or DAQ frontend) I want to measure their frequency response. Mostly gain, but knowing the phase can't hurt. My RTB2004 does this nicely, unfortunately only up to 25 MHz.
What options would there be for BW up to say 100...300 MHz (I am not a RF guy, so antenna preamps and matching is not relevant for me).

I have used a VNWA for this https://www.sdr-kits.net/introducing-DG8SAQ-VNWA3 , but the installation is somewhat quirky. Very powerful instrument though.
Probably other USB VNAs would also do. With NanoVNA output amplitude does not seem to be adjustable, which makes amplifier measurement quite uncomfortable (needs fiddling with attenuator kit).
LibreVNA https://eleshop.eu/librevna-2-ports-full-vna-100khz-6ghz.html looks interesting.

I don't want to invest in a proper bench top VNA as I neither have the need for a multi-GHz unit nor the bench space.
DIY via SCPI controlled RF gen and scope would be feasible, but a lot of work I'd like to avoid. Also a proper RF generator (sine output and wide range attenuator) would set me back $2000 on top.

Any ideas? Thanks!

Stick with the VNWA....
"Just hard work is not enough - it must be applied sensibly."
Dr. Richard W. Hamming
 

Offline MartinnTopic starter

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Re: Bode plot up to a few 100 MHz
« Reply #3 on: October 03, 2023, 01:36:06 pm »
Stick with the VNWA....
I don't own one, so I'd have to buy it. Feels a bit outdated though, installation by fiddling with USB audio codec settings is weird. But yes, tons of functions in the software and nice applications book available.

I've seen on ebay second hand portable VNA/SA (often used by service man for cellular towers/antennas).  The instruments were in working and sold for less than $500, with a calibration kit and some cables included.  A DIY would probably cost about the same and be less reliable.
Would you have an example? I quickly scanned ebay and found nothing even remotely at $500. Range was more like $5k-$40k.
 

Offline RoGeorge

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Re: Bode plot up to a few 100 MHz
« Reply #4 on: October 03, 2023, 01:46:41 pm »
No example right now sorry, it's been a while since I didn't look on ebay.  You'll have to hunt for a long time until some major provider or factory renew its inventory, or got sold at an auction.  Could take months or years until such bargain deals occur.

Offline nctnico

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Re: Bode plot up to a few 100 MHz
« Reply #5 on: October 03, 2023, 03:42:49 pm »
I've seen on ebay second hand portable VNA/SA (often used by service man for cellular towers/antennas).  The instruments were in working and sold for less than $500, with a calibration kit and some cables included.  A DIY would probably cost about the same and be less reliable.
These typically start at 5MHz or so. There are LF network analysers (Anritsu MS4630 for example) that work from less than 100Hz to a couple of hundred MHz and have high impedance (1M Ohm) inputs as well.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Offline tautech

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Re: Bode plot up to a few 100 MHz
« Reply #6 on: October 03, 2023, 04:25:01 pm »
Is 120 MHz enough ?
SDS2202X-E with SDG2122X.

To 1.5 GHz, SVA1015X Plus.
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Online mawyatt

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Re: Bode plot up to a few 100 MHz
« Reply #7 on: October 03, 2023, 07:27:47 pm »
The combo tautech mentions above should work, the SDS2000X+ and SDG2042X we have, both "enhanced", certainly do. The overall performance is quite good, albeit slow, and the Dynamic Range is impressive for a DSO.

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Offline tautech

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Re: Bode plot up to a few 100 MHz
« Reply #8 on: October 03, 2023, 07:59:10 pm »
Certainly SDS2000X Plus with its inbuilt 50 MHz Arb but with limited amplitude whereas with the right standalone will hit the 120 MHz Siglent DSO Bode plot limit.
Hence the suggestion of the cheaper 2ch 200 MHz SDS2202X-E for its 120 MHz Bode plot capability.

Still even the 2 ch SDS2102X Plus with its ~185 MHz -3dB BW plus SDG2042X hacked to 120 MHz total cost is right up near 1.5 GHz SVA1015X where the analyzer/VNA could be the better choice if the OP doesn't need another DSO.
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Offline pope

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Re: Bode plot up to a few 100 MHz
« Reply #9 on: October 03, 2023, 09:02:15 pm »
Why not sds1104x-e and SDG2042X? It can also do up to 120MHz, right?
 

Offline tautech

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Re: Bode plot up to a few 100 MHz
« Reply #10 on: October 03, 2023, 09:12:03 pm »
Why not sds1104x-e and SDG2042X? It can also do up to 120MHz, right?
Both hacked yes but does the OP need another DSO or a 4ch one ?
The little dearer SDS2202X-E also provides 50 Ohm inputs for better system matching and can be coerced to become a 350 MHz model.  ;)
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Online mawyatt

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Re: Bode plot up to a few 100 MHz
« Reply #11 on: October 03, 2023, 09:37:54 pm »
The OP mentioned scope and DAQ front ends, which might imply high impedance. Here's where the DSO and AWG might be a better choice that a VNA, which usually are centered around low Z of 50 ohms.

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Offline tautech

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Re: Bode plot up to a few 100 MHz
« Reply #12 on: October 03, 2023, 09:57:17 pm »
The OP mentioned scope and DAQ front ends, which might imply high impedance. Here's where the DSO and AWG might be a better choice that a VNA, which usually are centered around low Z of 50 ohms.
Then old school Bode plots might the only way past the Siglent 120 MHz limit but without a Phase measurement.
Cursors can then provide measurements but only a single one and not in a tabular multiple measurement format.
Maybe DSO Maths can help....need do some study.
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Online mawyatt

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Re: Bode plot up to a few 100 MHz
« Reply #13 on: October 03, 2023, 10:23:51 pm »
The OP mentioned scope and DAQ front ends, which might imply high impedance. Here's where the DSO and AWG might be a better choice that a VNA, which usually are centered around low Z of 50 ohms.
Then old school Bode plots might the only way past the Siglent 120 MHz limit but without a Phase measurement.
Cursors can then provide measurements but only a single one and not in a tabular multiple measurement format.
Maybe DSO Maths can help....need do some study.

Wonder if Siglent has considered upping the frequency range since many of the scopes are beyond 120MHz. They have the SDG6000X AWGs which go from 200 to 500MHz. If the scope can handle the higher frequency and one has the higher frequency AWG, then "seems" possible. Of course this from "someone" that doesn't have to do the work, as we see often here  ;)

Best,
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Offline tautech

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Re: Bode plot up to a few 100 MHz
« Reply #14 on: October 03, 2023, 10:29:52 pm »
I imagine beyond 120 MHz with a HiZ system good results might be difficult to obtain and much less so for a proper 50 Ohm impedance matched arrangement.
Those smarter than I should also contribute on this.  :popcorn:
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Offline joeqsmith

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Re: Bode plot up to a few 100 MHz
« Reply #15 on: October 03, 2023, 11:18:39 pm »
...
I have used a VNWA for this https://www.sdr-kits.net/introducing-DG8SAQ-VNWA3 , but the installation is somewhat quirky. Very powerful instrument though.
Probably other USB VNAs would also do. With NanoVNA output amplitude does not seem to be adjustable, which makes amplifier measurement quite uncomfortable (needs fiddling with attenuator kit).
...

Are you inferring that the VNWA3 does have a leveled output that can be adjusted?  Does it also have sinewave drive?  None of the low cost ones I have looked at do.  They also don't have bias Ts, are only 2-port 1-path .....   

Physical size, you never mention what sort of amplifiers but just thinking if you were playing with something in the kW range, I imagine the attenuators will be much larger than the VNA.   

Offline dophuc

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Re: Bode plot up to a few 100 MHz
« Reply #16 on: October 04, 2023, 02:21:35 am »
In the Rigol DHO800 Review Video "EEVblog 1566 - Rigol DHO800 12 Bit Oscilloscope" at minute 54:58, I see Dave using the Rohde & Schwarz MXO4 Series to evaluate the Bode Plot measuring probe with integrated 100Mhz waveform generator. That machine is the dream of many people because of its price when purchased with the "100 MHz waveform generator" option  ;D

https://youtu.be/S8jrpCoZyx8?si=98JFR9S5V3ep6WYF&t=3298
 

Offline tautech

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Re: Bode plot up to a few 100 MHz
« Reply #17 on: October 04, 2023, 02:45:11 am »
In the Rigol DHO800 Review Video "EEVblog 1566 - Rigol DHO800 12 Bit Oscilloscope" at minute 54:58, I see Dave using the Rohde & Schwarz MXO4 Series to evaluate the Bode Plot measuring probe with integrated 100Mhz waveform generator. That machine is the dream of many people because of its price when purchased with the "100 MHz waveform generator" option  ;D
200 MHz model = € 8,280  :o
https://www.batronix.com/shop/oscilloscopes/Rohde-Schwarz-MXO44-242.html
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Offline dophuc

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Re: Bode plot up to a few 100 MHz
« Reply #18 on: October 04, 2023, 03:13:08 am »
In the Rigol DHO800 Review Video "EEVblog 1566 - Rigol DHO800 12 Bit Oscilloscope" at minute 54:58, I see Dave using the Rohde & Schwarz MXO4 Series to evaluate the Bode Plot measuring probe with integrated 100Mhz waveform generator. That machine is the dream of many people because of its price when purchased with the "100 MHz waveform generator" option  ;D
200 MHz model = € 8,280  :o
https://www.batronix.com/shop/oscilloscopes/Rohde-Schwarz-MXO44-242.html

This price does not include the "Waveform generator" and "Bode Plot" options, adding these 2 options costs about €3400 excluding tax  ;D
 
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Offline MartinnTopic starter

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Re: Bode plot up to a few 100 MHz
« Reply #19 on: October 04, 2023, 07:01:50 am »
Are you inferring that the VNWA3 does have a leveled output that can be adjusted?  Does it also have sinewave drive?  None of the low cost ones I have looked at do.  They also don't have bias Ts, are only 2-port 1-path .....   

Physical size, you never mention what sort of amplifiers but just thinking if you were playing with something in the kW range, I imagine the attenuators will be much larger than the VNA.
Yes, VNWA has an adjustable output. See this document on page 241: https://www.sdr-kits.net/documents/VNWA_HELP.pdf
Here's an example of what I want to accomplish:
https://www.eevblog.com/forum/projects/measuring-switch-mode-supply-noise-hp461a-replacement-ada4895/msg4652395/#msg4652395
The last graph (frequency response up to 200 MHz) was measured using a VNWA. Power levels are small signal only, so no kW attenuators.
To my knowledge none of the low cost (< $1000) VNAs have a sine output (VNWA3 certainly does not).
If you know of a RF signal generator with sine output and programmable attenuator for < $2000, let me know.
 

Offline MartinnTopic starter

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Re: Bode plot up to a few 100 MHz
« Reply #20 on: October 04, 2023, 07:04:49 am »
In the Rigol DHO800 Review Video "EEVblog 1566 - Rigol DHO800 12 Bit Oscilloscope" at minute 54:58, I see Dave using the Rohde & Schwarz MXO4 Series to evaluate the Bode Plot measuring probe with integrated 100Mhz waveform generator. That machine is the dream of many people because of its price when purchased with the "100 MHz waveform generator" option  ;D
200 MHz model = € 8,280  :o
https://www.batronix.com/shop/oscilloscopes/Rohde-Schwarz-MXO44-242.html

This price does not include the "Waveform generator" and "Bode Plot" options, adding these 2 options costs about €3400 excluding tax  ;D
I recently purchased a R&S 300 MHz RTB2k "fully loaded" (with good discount - certainly being helped by some friendly competition from the eastern part of the world), so I am not quite looking for upgrading this.
 

Offline tautech

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Re: Bode plot up to a few 100 MHz
« Reply #21 on: October 04, 2023, 07:20:47 am »
If you know of a RF signal generator with sine output and programmable attenuator for < $2000, let me know.
As Mike pointed to earlier SDG6000X and entry into this range is 200 MHz model but can be coaxed to 500 MHz.
Then with your DSO old school Bode plot to 300 MHz would be very possible like Dave shows in this old video:
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Offline MartinnTopic starter

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Re: Bode plot up to a few 100 MHz
« Reply #22 on: October 04, 2023, 07:24:01 am »
The OP mentioned scope and DAQ front ends, which might imply high impedance. Here's where the DSO and AWG might be a better choice that a VNA, which usually are centered around low Z of 50 ohms.
Yes, I am thinking more of high impedance amplifiers, like this small design: https://www.eevblog.com/forum/projects/measuring-switch-mode-supply-noise-hp461a-replacement-ada4895/msg4652395/#msg4652395
But where do you see the problem with 50 ohms? High Z input can be terminated with 50 ohms (input noise changes of course, but that's not relevant here). Output needs to be capable of driving a 50 ohms load, which might be more of a problem. I had to include cable drivers in my "HP461A" LNA design.

I imagine beyond 120 MHz with a HiZ system good results might be difficult to obtain and much less so for a proper 50 Ohm impedance matched arrangement.
I agree, that's what I wrote "few 100 MHz", which I think should be achievable with proper layout.

Is 120 MHz enough ?
SDS2202X-E with SDG2122X.

To 1.5 GHz, SVA1015X Plus.
Interesting options. As I wrote I just bought my RTB2K and certainly will not replace that. SDG2122X: Nice, but a bit limited at 120 MHz.
What about the SDG6022X: Can it be "upgraded" to 350 or 500 MHz as well? EDIT answered by tautech

SVA1015X lists "discontinued" at Batronix. Tons of other options though:
https://www.batronix.com/shop/siglent/all-spectrumanalyzer.html
However usable are VNA functions in these "classical" SA?
Also, I own already a HMS1000 spectrum analyzer (no TG) I purchased for EMC precompliance, would need to get rid of that first (market value probably near zero due to Chinese competition and lack of magic R&S label).
 

Offline MartinnTopic starter

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Re: Bode plot up to a few 100 MHz
« Reply #23 on: October 04, 2023, 07:29:13 am »
As Mike pointed to earlier SDG6000X and entry into this range is 200 MHz model but can be coaxed to 500 MHz.
Then with your DSO old school Bode plot to 300 MHz would be very possible like Dave shows in this old video:
I also considered signal generator+DSO, but instead of the crude sweep method Dave shows I thought of running a sweep via remote SCPI control. Set frequency, acquire reference and output channels, calculate amplitude/phase, next frequency. But that would be a lot of work to do the interfacing and the basic sweep method might be good enough!

I will definitely look into the SDG6000X!
 

Offline tautech

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Re: Bode plot up to a few 100 MHz
« Reply #24 on: October 04, 2023, 07:33:43 am »
SVA1015X lists "discontinued" at Batronix. Tons of other options though:
https://www.batronix.com/shop/siglent/all-spectrumanalyzer.html
:-//  It's a current model:
https://www.batronix.com/shop/spectrum-analyzer/Siglent-SVA1015X-VNA.html

Quote
However usable are VNA functions in these "classical" SA?
Same HW as SSA3015X Plus.  ;)
SVA1000X models have a # of modes with SA and single active port VNA being core functions that provide for a range of S11 and S21 measurements. Optional but 120hrs of trial use are DTF and EMI modes.
« Last Edit: October 04, 2023, 07:35:26 am by tautech »
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