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Random Wire Tuning - Take 2


Dave W0DCX
 

After reviewing the previous thread on this topic, I felt somewhat uneasy about my contribution to the discussion.  I felt as if my reporting became somewhat desultory.  So, I have done some more analysis and would like to share it along with some additional context.  Keep in mind, I am trying to optimize a wire antenna for DIRECT use with my KX2 while NOT using my 9:1 unun.  When I used the unun I can get just about any length wire to tune okay.  So I am trying to create a minimal operating system here.

The original study under discussion used a 72-foot wire.  Why did I select this length?  For one thing, according to the random wire antenna links, one of which was shared by another contributor, 71-72 feet is suggested as one of the preferred lengths in order to avoid 1/2 wavelength multiples on any common HF band.  1/2 wave multiples present high impedances to the transceiver.  The second reason I selected 72 feet was that it is exactly the distance from my transceiver to the high branch of a tree in my backyard where I have a nylon haul line installed.  This length of antenna wire allows me to get the distal end of the antenna as high as possible (33 feet), all the way up to the branch.

Well, 72 feet worked really well on 30 meters, and if I was going to work just 30 meters this is the antenna I would haul up the tree.  Great SWR, great tuning, and as high as possible.  BUT there were tuning issues for me on other important bands like 20 meters and 40 meters.  So today I tried something a little different.  I decided to trade-off the maximum antenna height for a more useful antenna length, one that might tune better on more bands.  I selected a 50-foot wire which was able to get the distal end of the wire up to a height of about 28 feet.  I used my 29-foot counterpoise wire in conjunction with this antenna.

Below is a Table showing my results from NanoVNA measurements and actual KX2 ATU tuning results.  The bottom line is that the 50-foot wire was quite workable on all the bands I tested - EXCEPT FOR 30 METERS where my 72-foot wire excelled.  I can live with that.  Also, except for 10 meters where reactance was slightly inductive, reactances all on other bands were capacitive.  The big caveat is that I do not fully understand or trust what the NanoVNA is telling me.  But I am presenting the numbers as raw data and also some resulting impedance calculations I performed.  I just want to put the numbers out there and see if they make sense to anyone else.  Perhaps the VNA is not functioning accurately on all frequencies.  Perhaps I still not yet know how to use it properly.  Also, I understand that using different lengths of counterpoise or changing the counterpoise positioning relative to ground and the antenna wire may have impacts on the results.

Well, here is my 50-foot wire antenna Table from this morning.  (Excel document as an attachment, too).  While futzing with things I made two QSOs on 40 meters - Florida and Georgia.  Your mileage may vary.



73,
Dave W0DCX


Curt
 

This interests me, although don't own a KX2.  My K1-4 has 15, 20, 30, and 40M.  It also has a KAT1 internal tuner.  I usually use a SOTA tuner to load a 34' wire in a tree with the internal tuner disabled.  No radials.  For 30M I clip in an additional 16 feet.  This scheme works very well.  As simple as SOTA tuner is, it is too bad an internal version for the K1 was never offered. 

I have been wanting an antenna requiring no devices external to the radio and using the internal tuner, looks like 50' with 29' counterpoise might work for 15, 20, and 40M.  My only concern is it isn't mentioned by Cebik, unless this is a "special case" for an inverted L.

I seem to recall the KAT1 manual suggesting a 51' element with a 1/4 wavelength counterpoise @ 40M or about 34 feet.  I also encountered suggestion for deploying a horizontal loop, which wouldn't require any counterpoise.  Of course a loop would be more of a pain to deploy than a single wire.  But, Cebik mentions them and I use a 40M FW loop on all bands effectively for the home station.

72, Curt KB5JO