Sunday, September 29, 2019

More comparisons with NanoVNA and Keysight analyzer

I built a little test jig this morning to allow plug-in low-pass filters
designed for the G0UPL Ultimate 3S to be easily swapped and measured. I have 8 of these filters for various bands, six of which are currently installed in my U3S.

The other two are for 15 and 30 meters and it is these I used to
compare both the David and the Goliath (at least in terms of price - they're both small) of the analyzers I have on hand.

It didn't take long for me to realize that having the test set-up and the NanoVNA will allow me to more accurately wind the toroids for such filters in future QRP projects as it is easy to see the effect of compressing or spreading the windings in real time.

Also, if an additional, or one less, turn is needed, the result can be verified before installing the filter into the circuit.

I'll be making plots of the other filters soon - I think I'm now pretty much trusting the NanoVNA without needing further verification of the results from the Big Guy - at least at HF frequencies.

In fact, it looks like this device is - for a price of $50 and a weight of 2.6 ounces - going to replace my antenna analyzer, RF bridge and noise source (no, I don't mean you, Naomi...) as well as offering other functions to boot.

Here are comparisons of the two filters I've tested so far (I know that the 30m band ends at 10.150 MHz but the VNA's 101 points-measured limit didn't allow me to put a marker exactly on that spot with such a wide range selected):
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Low-pass filter for the 30m band

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Low-pass filter for the 15m band

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I also wanted to test a 1.03 GHz bandpass filter as well. It falls outside the NanoVNA's upper limit of 900 MHz but I thought I'd be able to select the higher frequency anyway just to see what the results would be.

No can do - 900 MHz is the upper selectable frequency.

So I grabbed the least-used piece of radio gear I own - a V/UHF mobile antenna. Specifically, it is a Comet SBB7 magnet mount whip.

Again, with a wide range selected, the 101 measurable points doesn't allow for much resolution in where markers can be placed. The solution is to use a narrower range but here I wanted to see the big picture rather than zoom in for detail.


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