#576

Episode 576
WARNING: do not input more than 0dBm (1mW) power into the NANOVNA
Using the NANOVNA to measure the gain the frequency response of a small amplifier
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[@MrBanzoid]

I bought a cheap attenuator board from Bangood. It does 0, -10, -20 and -30 dBm. Obviously it's not lab spec but it worked OK when I used it to measure the gain of cheap RF amplifier boards without zapping CH1 on my nanoVNA. You can link the sections with SMA jumper cables to a maximum of -60 dBm.

[@elioalcala4371]

I WONDER how much was tha t amp? & is THERE ALSO +60 db? For recoger of Long extensión cable losses?

[@elioalcala4371]

ALSO, how MANY volts

[@samuellourenco1050]

You can measure the 60 dBm board by using a set of 20 + 30 dB attenuators at the input of the amplifier and a 10 dB attenuator at its output. It should work. I did something similar in a recent video on my Bloguetronica channel (on Oddysee). In my case, it was a 30dB plus amplifier that accepted a 0 dBm signal at its input. To be safe, I've used a 10 dB attenuator at the input and a set of two 10 + 20 dB attenuators at the output. That gave me an attenuation of 40 dB. As I said in a comment before, your video was the inspiration.

[@elioalcala4371]

We learn so MUCH, greetings FROM México/ I am searching for the RIGHT amp if I WANT TO cope with a Long cable -LM400 INSTALL OF 25 MTS, MAYBE I WILL LOOSE AROUND 10dB!!! ? Can I. Recover tha t? Very clear imagen, you do explain so GOOD!!! Thanks

[@mikekennedy5000]

I was wondering if it's possible to calibrate the VNA with the 20 dB attenuation inline. Then when you connect the amplifier you would get the "true" output of the amplifier? Would this be correct outcome? I would understand that the SNR ratio at the VNA S21 end would be reduced because of the attenuation during calibration, but would this be a concern? Because we are only interested in Log/MAg on the thur, at relative high amplitude's. And as always! Thanks for all your video's, it really helps me understand better the concepts! Thanks, MikeK

[@IMSAIGuy]

I think that would lead to trouble. I would guess the nano is set to expect a certain range of numbers. your question points to the fact that all that test equipment I own can be HPIB controlled. it is the very reason that each test and setup is unique and things like compensating for an attenuator in software is easy to do. I've thought of doing a video on an automated HPIB test but haven't got around to it. I did do a video where I controlled a Keithley 2400 via serial port.

[@pentachronic]

I would guess that since you are messing around with the feedback loop the NanoVNA would increase it's Ch.0 output to compensate to get 0dBm (or similar) on Ch.1. As a result the front-end Ch.0 amplifier would saturate and look like garbage.

[@IMSAIGuy]

@@pentachronic your guess is wrong. there is no feedback loop. the nano keeps the ch0 output the same and just monitors ch1

[@pentachronic]

@@IMSAIGuy How does it calibrate ?? Calibration is a feedback loop which stores the data (albeit in software) for a known input and corrects for it right ? Normalisation is a form of feedback from my understanding of control systems.

[@IMSAIGuy]

@@pentachronic All VNSs calibrate with calibration standards. Open/short/load. the calibration is done for S11. then a cable connecting the ch0 and ch1 does an S21 transmission cal. the cal is over a range of frequencies. This is a simple VNA and does not include S22 or S12

[@ElectronicsCuriosities]

Great explanation thanks 👍🏻😊

[@pinkypink2410]

you are such a precious human being! thank you sir, it was very useful

[@muckabeaga2536]

Hi IMSAI, love the content! On the subject of: "can you do videos on, ...", any chance you could do a video on measuring the output impedance of various elements (active circuits in particular). When building RF circuits you're often trying to match impedances between circuit sections. You design for a particular impedance, but it would be nice to verify with an actual measurement. You often see expensive variable reactive loads used to compute this, not sure if there's a "poor mans" version? Keep up the good work!

[@IMSAIGuy]

well you're getting out of my knowledge zone. I've never done RF circuit design and measuring s-parameters of active devices sounds tricky. I've thought of trying to build a matching LC for the SAW filter I have. seems easy to do the C part but the L part might require more knowledge of RF inductors than I have. Having the VNA does make it much easier to do this stuff so maybe I'll have to try.

[@muckabeaga2536]

@@IMSAIGuy Yep, same here, I'm certainly not an RF guy. I do stumble into this from time to time building circuits for amateur radio. I think the classic approach is to measure the unloaded output voltage, then measure again with a known load. You end up with a simple voltage divider with the output impedance as the unknown (w2aew did a video some time back). Works for low frequencies, but gets progressively inaccurate at higher frequencies. Anyway, thought it might be an interesting application for a VNA. Keep up the good work.

[@IMSAIGuy]

that works for the real part of the reactance but not the imaginary. no phase

[@Parva_Goldfinch_ALG]

Can I connect my amplifier to the phone charger with USB cord instead a battery?

[@elioalcala4371]

I WANT TO recover losses x lorawan signal install Thks

[@JD-eq1gk]

Guy, I recently bought the LiteVNA64 and I can't find any info on the port 0 output power. I'm thinking I could put it in CW mode at a frequency within the fundamental range of the internal clock and using that as an estimate, knowing the Si Labs clock uses weaker harmonics at higher f's, measuring it on a properly padded SA. What do you think?

[@IMSAIGuy]

I did some videos where I measured that. Can't remember the value. around 0dbm I think. the port 1 power is way hot, be careful. I did a video on that too. I have not measured your exact model though. I have a playlist for all my nanovna videos

[@andrewverran3498]

I am newbie, could i use the nonaVNA to troubleshoot a generic 1.5v cb radio power mics circuit? Regards Andrew

[@IMSAIGuy]

no

[@daviddawkins1]

Thank you so much for sharing. You make great videos. Thank you.

[@frankreal2258]

Hello, you can make one video to make one power source to calibrate a homemade power meter in the absence of an expensive test instrument, for the frequency the GPS disciplined oscillator is affordable but for the power source some good idea? Thank you for your video and experience.

[@IMSAIGuy]

coming soon

[@chrisbart5316]

You are the best. In this video at 7:51, you say you are putting in a short, but you are using a through connector from Channel 1 to Channel Two.

[@IMSAIGuy]

you are right, sorry

[@rjrodrig]

How about output return loss and input return loss.

[@asmahoseini4393]

خفه کردی ما رو... اصل کلام و بگو

[@novydrassel3005]

Very good !

[@frankreal2258]

Thank you

[@elioalcala4371]

Where. did you bought your n vna?

[@IMSAIGuy]

www.randl.com/shop/catalog/index.php?manufacturers_id=142&osCsid=fu3f0ql3nieitil9ir623bmcb6

[@bloguetronica]

That will surely be my use case when my newly bought NanoVNA arrives. I'll have to use attenuators, mainly at the output of the PA.

[@bloguetronica]

As an update, I did use it to characterize a PA, and worked a treat!

[@IMSAIGuy]

What parameters did you analyze? gain vs freq. anything else?

[@bloguetronica]

@@IMSAIGuy Basically, I was able to measure gain versus frequency, plus the Smith chart of the input, which is not very relevant, because I was measuring essentially the effect of the attenuator at the PA's input, with little contribution from the input stage. The setup is here: twitter.com/bloguetronica/status/1315699061937319939/photo/1 . And the results can be seen here: twitter.com/bloguetronica/status/1315736220761194500/photo/1 . It is a very nice tool!

[@__--JY-Moe--__]

couldn't you use a Multimeter? to check the power. before you run your tests on your VNA?

[@IMSAIGuy]

No. Multimeters will not measure high frequency

[@rjrodrig]

You need a high frequency power meter. DMM are good for DC only

[@__--JY-Moe--__]

Thanks 4 the replies! ok, sorry...I see now..;) I need an oscilloscope! or NVA...

[@rjrodrig]

@@__--JY-Moe--__ depends on what you are doing. Oscilloscopes measure time domain signals. VNA is a frequency domain measurement. You also have Spectrum analyzer for frequency domain analysis. So it depends on what you are trying to accomplish 🙂

[@ahbushnell1]

can you calibrate with the attenuator installed.

[@IMSAIGuy]

see comment below

[@Aron102]

Great video thanks for sharing

[@Aron102]

Great well done not interested

[@dionisisch]

Hi!! Nice video! Can I use an amplifier to have more witnesses - receive signals in an rf lorawan receiver? Helium

[@IMSAIGuy]

of course

[@dionisisch]

@@IMSAIGuy can you please send me a link ... an example of what to use - buy? The frequencies are 868-870mhz

[@IMSAIGuy]

www.ebay.com/itm/184351476023?hash=item2aec344937:g:cGMAAOSwfHJe~4up

[@RolfAnderssonLMY]

I have an IMSAI 8080 too, as well as 2 NanoVNAs...

[@IMSAIGuy]

good job!

[@RolfAnderssonLMY]

@@IMSAIGuy Thanks!! :)

[@CodeJeffo]

I really love your education style. Happy to discover your channel. Wonderful content.

[@HalfLife2Beta]

so if you calibrate through with a 20 db attenuator does it allow u to measure amplifier gain without breaking VNA ? aka 20 db attenuator = 0 db after cal so with amp it would show directly the gain

[@IMSAIGuy]

Yes that works fine. The only issue is the calibration is done at a level 20 dB lower and so the cal will be noisier. If your VNA has lots of dynamic range this is not a problem.