Re: The mysteries of tuning a random wire


Don, W9EBK
 

Dave,
There are too many variables here for me to make a suggestion with much confidence.  I don't know what model VNA you are using but if it's a $50 mini-VNA it might be that the numbers you are getting are not accurate.  About a year ago there was an article in QEX where someone thoroughly tested one of those.  The results showed amazing accuracy most of the time,  but there were some situations where the numbers were Very wrong.  As I recall this was caused by measuring loads that were resonant on a harmonic of the test frequency.  The solution to this problem would be to use a bandpass filter for each band,  but in your case the filter might change the xL or xC of the device under test, so that's not likely to work. 

Don, W9EBK 

On Wed, Jun 17, 2020, 1:41 PM Dave W0DCX <cwqrp73@...> wrote:
Taking the next step I took N5IB's advice and took the impedance calculations to completion.  I'm not sure if the VNA will do this for me, but for now I constructed an Excel spreadsheet where I can just plug in the values the VNA gives me and get the final results.  I've checked the calculations a few times and don't find any errors.  The results still puzzle me.  Some of the numbers I can rationalize from the actual behavior of my ATU but then some of the numbers don't make sense.  I may be doing something wrong, or maybe there is some sort of voodoo going on in my wires.

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