Products > Test Equipment
Affordable <200MHz PDN analysis / impedance measurement hardware?
joeqsmith:
The first thing I noticed when I took their new H4 apart, the manufacture added two capacitors in series with the connectors. It's still AC coupled at the mixers. No idea what they are thinking.
I went ahead and reworked their VNA, removing those input caps, adding the TVSs and additional caps, similar to what I had done with mine. It's performance is no where near what I get with mine.
They had originally purchased two of the NanoVNAs and gave one to me to get started. I plan to steal the parts from theirs like I did with my H4 after it was damaged. My guess is the synthesizer but maybe there is a problem with the firmware configuring the MS part.
Shown is flippers H4 after my mods with 30Hz IFBW, 401pts, 1.6-10kHz, both ports terminated, same firmware but MS. Thru cal. Scaled -50 to -100. I expect yours would be similar with 30Hz.
joeqsmith:
My old H4 also had a mezzanine board that was used to interface between the main PCB and the LCD. From photo, you can see the TX input goes from the connector to R10. Yours may have a capacitor there for what ever reason now. The same for port 2. Note, this was taken after swapping mixers but prior to adding caps and TVSs.
Compared to the 75dB I previously showed with Solver, using 30Hz IFBW with this old hardware, gets us an easy 80dB below 5KHz, and 90dB above. Of course, it takes a long time to sweep.
I'm surprised that none of this was mentioned in the groups.io or by the manufactures, but then again.... Keeping my fingers crossed that swapping the synthesizer will get my friends new H4 to perform as well as mine.
joeqsmith:
This was the only post I found on the change. No mention of the low frequency performance.
--- Quote ---Hugen,
Hello Salva, Due to Si5351 out of stock, we started to use MS5351M to replace SI5351A-B-GT. In order to obtain the widest possible range of measurement frequencies for the NanoVNA, we have extended some usage ranges beyond those specified in the Si5351 manual. Although the performance specified in the MS5351M manual is almost identical to that of the Si5351A-B-GT, they differ slightly for the parts that go beyond the manual. Simply put the MS5351M has a slightly higher VCO frequency than the Si5351, the MS5351M has a steeper square wave edge, and the MS5351M has slightly lower phase noise than the Si5351. With targeted software adjustments, it is possible to get slightly better results with the MS5351M than with the Si5351. Since the frequency range of the VCO is slightly different, the frequency points for switching different divider are different when using Si5351 and when using MS5351, so if the software's signal generator MODE is different from the actual chip installed, it will generate some anomalies around the divider switching frequency.
You can set the measurement frequency to 50kHz-900MHz and check if some abnormal spurious is generated. If there are multiple abnormal spurious, the signal generator mode of the software is not the same as the actual installed chip. On our NanoVNA-H and NanoVNA-H4, if MS5351M is used, we add the MS suffix to the version number on the label of the backshell, such as 3.6_MS or 4.3_MS.
--- End quote ---
https://groups.io/g/nanovna-users/topic/88101278#msg26386
inevitableavoidance:
--- Quote from: joeqsmith on November 17, 2024, 02:59:50 pm ---
--- Quote from: inevitableavoidance on November 17, 2024, 11:22:40 am ---I'm getting nowhere near that figure - 10dB per division:
...
Where do I find the revision and synthesizer?
--- End quote ---
The back of the unit should have the hardware revision and possibly an _MS. You can also select Config, Expert Settings, More. At the top is should show the synthesizer selected (MS5351 or Si5351).
You can try to set the IFBW to 30Hz which should at least remove the pattern you are seeing.
--- End quote ---
That’s way better indeed:
It’s a 4.3_MS
joeqsmith:
Thanks for checking. That's on par with my friends. I should have his original NanoVNA in a few days. I'll post the results once I start swapping parts.
If it is the clock generator, it doesn't really help you other than maybe someone you know might be willing to swap you their older unit to get a brand new one.
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