Strange behavior with Nanovna - Page 1
Forum section: electronics / rf-microwave

author: WPXS472
author_rank: Regular Contributor
timestamp: December 08, 2020, 02:02:05 pm
content: I recently bought a newer model Nanovna, the one with type "N" connectors and extended frequency range. I loaned it to a former co worker so he could check it out with his better quality equipment. After a week, I called to see what he thought. He said he didn't really check everything, but he thought it was worth the money I paid. He commented that the level measurement seemed very accurate, but he didn't check it over the whole frequency range. Then, he said the frequency was off by 5.6 MHz. I thought this was odd. I assumed that it used some kind of TCXO for its reference and might be off a few PPM, but 5.6 MHz at a pretty low frequency didn't sound right. So, I hooked it up to my trusty Racal 1992 counter, set it for CW frequency, 100 MHz. The counter just displayed random numbers. Surely this thing puts out enough to trigger my counter. So I select 10 MHz, and it displays more or less 10 MHz. I didn't note the exact frequency, but there were zeros after the decimal point. Good enough. I went back to 100 MHz, set the number of points to 1, it displayed 101 points. I set the number of points to zero and it displayed 2 points. Odd, I thought. Still no counter display. So, I connected to my spectrum analyzer and the frequency seemed to be all over the place. Actually, it didn't look like a single frequency jumping around, it looked like a bunch of rapidly shifting frequencies. No wonder the Racal couldn't lock up on it. Checked 10 MHz, same thing. Now, I am wondering if this thing will even be usable. Has anyone else with one of these seen the same thing? I doubt if there was even a warranty. I will do a cal and try measuring a few filters to see what I get.

author: thinkfat
author_rank: Unknown
timestamp: December 08, 2020, 02:10:09 pm
content: Very likely the output is pulsed. That will confuse any regular counter quite a bit. A spectrum analyzer will see a lot of lines as normal with an ASK (or OOK) signal.

author: WPXS472
author_rank: Regular Contributor
timestamp: December 08, 2020, 03:08:56 pm
content: That sounds reasonable. But why would a CW output be pulsed? I am still perplexed.

author: Bud
author_rank: Super Contributor
timestamp: December 08, 2020, 03:25:57 pm
content: Connect to the oscilloscope and see if it shows sweeped frequency output, that will explain why the counter and spectrum analyzer behaved as they did.

author: thinkfat
author_rank: Unknown
timestamp: December 08, 2020, 03:34:12 pm
content: Quote from: WPXS472 on December 08, 2020, 03:08:56 pmIf it's a SAA2 based design, those don't do true CW.

author: mawyatt
author_rank: Super Contributor
timestamp: December 08, 2020, 05:13:47 pm
content: Yes the output is a pulsed output.If you load the latest firmware 20201013-32077fd this pulsed output becomes a CW signal if you select CW Freq from the Stimulus menu.I get 999.994888MHz with a 1GHz CW frequency selected, reading from my SA (don't have a counter than goes that high), and 99.99990MHz from my DSO counter with 100MHz selected.Best,Edit: Also get 99.999884MHz, 9.9999883MHz and 999.99882KHz with 100, 10 & 1MHz selected reading with the counter function on the SDG2042X. The spectrum is pretty good also for the SAA 2N as you can see from the images.

author: WPXS472
author_rank: Regular Contributor
timestamp: December 08, 2020, 08:40:34 pm
content: In that case, it seems I need to update my firmware. I'll look into that. I just assumed, yes, I know. Never assume, that since I just bought it, it would have the latest firmware. I know VNAs are often looked upon as swept measurements, but a measurement at a single frequency is often all I need. I will inform my former co worker that he was wrong about the frequency.