I've been recently trying to piece together all the various conflicting information on balun and unun measurement with the NanoVNA. The problem is not a lack of tutorials, videos, instructions...it is the opposite -- there are hundreds of such things available. However, they don't agree with each other. And, even on this one forum (and other NaoVNA forums), when the question comes up for a definitive guide, different sets of links are provided! It appears there ISN'T a definitive guide, rather just a growing assortment of good/bad/ugly opinions. So it becomes a problem of "which advice should I believe?"
To give some examples:
- some folks how long leads (12-24") being used to connect the DUT to the nano, other say you need to minimize these lengths (<4"). Still other says it doesn't matter because when you calibrate the Nano it all comes out in the wash.
- Some instructions show what appears to be a metal plate "shielding" the nano from the DUT. Or maybe this is just a convenient mounting plate for frame-mount connectors? I haven't seen the explanation for why this plate is used, not everyone has one, but the K9YC Choke Cookbook shows a picture of it and I think k(YC has put more thought into baluns/ununs than almost anybody so I value that picture -- still don't know why to do it, but see that he is using it in his measurement jig.
- Some guidance uses just one Nano port, others use both. Some have PL-259's on both coax ends (for coax-wrapped baluns) which they plug into SO-230-SMA adaptors straight into the Nano.
- Others demonstrate measurements with single-conductor wire-wrapped baluns; still others have double triple, or quad wrapped single conductors -- which wire ends do you connect to in these cases? All of them, or should each one individually measure the same?
- Some guides show the use of resistors or capacitors in series or parallel with the DUT -- are they always needed? What values? Most videos do not show them being used, but enough do that I wonder if they improve accuracy. (Kill parasitic capacitance or some such.)
- What Nano menu items are selected for measuring the effectiveness of a balun/unun? Logmag, phase, smith, resistance, reactance, .... The thing we're actually looking for is Impedance, but the Nano doesn't offer that directly. What other nano settings are needed? Range offsets, etc??
So, you see, this is not a simply-answered question. The common re-occurrence of the question is enough proof of that. And reading thorough the boatload of possible linked answers is very time-consuming.
If anyone knows of a guide/video that specifically answers each of the above questions then please share that one, definitive guide. Is there any plan that shows how to build a generic balun/unun/choke test fixture that can be re-used time after time on an assortment of such devices? And what sets this recommendation apart from all the others (showing different things?) Why should I believe the specifically recommended one?
