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A full wave open stub coaxial loop 80m

nfsus

Yeah its turned off, touch it
May 9, 2011
474
241
53
47
Arkansas
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Reactions: brandon7861

Didn't read it all, but tried anyhow. Had a half wave 11m jumper in the truck and had to know.

First thing I did was calibrate at the port saver. Then, I attached the tee and port extended the measurement plane to the tee. I initially did the calibration from 20MHz to 80MHz, but had to bump the stop up to 120MHz. I did not recalibrate, but that doesn't affect it enough to move that dip. Had I been measuring something more important, I would have. The wear on my ports wasn't justified by the minimal change in accuracy in this case.

I then connected a 50Ω terminator to one side of the tee to confirm my jumper length. At 27MHz, a half wave coax looks like an open leaving the terminator the only thing seen at the tee by the VNA. Where SWR is 1, the coax is a half wave or multiple. Coax is thus 1 wavelength at 54MHz.
IMG_20240922_143209094.jpg

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Then I removed the terminator and stuck just the center connector into the tee to make the loop antenna as described. I did get a nice match, 20MHz worth of BW under 2:1 SWR. Only thing is that it wasn't at 54MHz. It was up around 80MHz.
IMG_20240922_143522783.jpg
IMG_20240922_143506646.jpg

This was sitting on my wood pile and maybe getting it up higher would have shifted the center frequency, didn't have time to test. I also did no measurements of the pattern, figured a better setup was necessary for that.

The important part is that the power goes somewhere and its definitely worth further investigation. Wish I had time today.
 
I find it interesting that my smith chart plot and SWR trace came out just like it was shown in the patent photos, even though they used UHF and I used HF near the ground.
smith loop ant.png
 
its a read for sure. i hate patent papers. too much repetitive nonsense. i just hung a delta 80m and im interested in this matchless design as it should drop a fair amount of loss off of it. im not sure if youd get much harmonic work out of it though so it might be just a 80/40m but thats fine really since its going to be a nvis anyway.

now i have to decide if i want to spend some money on 66% velocity factor coax. the guy who told me about it said that he tried it with 80vf coax and it didnt do it right.
 
What would happen if you tried it with old 75 ohm tv coax? The smith chart trace whirled around the lower side of center, so maybe using 75 will move it to the right a little.
 
I believe it’d change your impedance for one. Then you’d be looking at having to match it. Which would defeat the matchless design. Then you’d have to consider the power handling capability bet even the coax. I’m not even sure exactly what you could push through the other one.
 
I’m thinking about trying to adjust the length of the antenna element using rg8x vs 58 since I’ve got a bunch of 8x. I’ll start with 144mhz. Should just need to make it 14% longer than the usual.

Edit

Oh thinking about it, how much difference would 25 ohms make in the grand scheme? Without knowing the resistance of the feed point you wouldn’t know what the impedance would be by mixing 50&75 ohm feeder and element. We need someone to model it
 
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