Another directional RX loop

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Andrew (grayhat)
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Re: Another directional RX loop

Post by Andrew (grayhat) »

Also, a DUE note !

The idea came after a request from my dear friend Kostas (SV3ORA); he asked me if it was possible to make the "SULA" smaller and less visible (basically it shouldn't look like an antenna) and told me that ideally he needed some given dimensions

At first, knowing all the hurdles and issues I faced while designing and optimizing the "SULA" I told him that it wouldn't be possible or, better said, that such a reduced size antenna wouldn't offer acceptable performance at lower frequencies, but then... being the kind of "hard headed" folk I am, I told myself... why not, let me try

So after some fiddling with NEC, changing designs, mailings (with Kostas), scratching head... ok, all the usual "process", I finally came out with the design you tried, and given your results, it seems to work decently well :D

A request, if I can dare; would you be so kind to try the "nulling" of the antenna ? I mean, aim it at some given station, then record the signal and try turning the antenna so that its backside "NULL" will be oriented toward the station; does it really "cancel out" the station or, in any case, is there a noticeable signal attenuation (as I think it should be) ?
Egil - LA2PJ
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Re: Another directional RX loop

Post by Egil - LA2PJ »

Andrew (grayhat) wrote: Wed May 15, 2024 1:28 pm If you can/want, it will be interesting to see a video comparing that antenna with the stock one (or with some other antenna)
Right now I am in Trondheim, but I am planning to do just that when I return home at the end of this month.

Forgot to say that I made the SULA made with some break line had had at hand, and placed 3m above ground on a small rotator. But I hadn't made it strong enough mecanicly, so one of the winter storms pulled it apart. It was a really good receiving antenna, so I plan to make a new one with more sturdy materials, so it can survive the harsh winter weather on an island on the west coast of Norway.
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Andrew (grayhat)
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Re: Another directional RX loop

Post by Andrew (grayhat) »

Egil - LA2PJ wrote: Wed May 15, 2024 3:30 pm
Andrew (grayhat) wrote: Wed May 15, 2024 1:28 pm If you can/want, it will be interesting to see a video comparing that antenna with the stock one (or with some other antenna)
Right now I am in Trondheim, but I am planning to do just that when I return home at the end of this month.

Forgot to say that I made the SULA made with some break line had had at hand, and placed 3m above ground on a small rotator. But I hadn't made it strong enough mecanicly, so one of the winter storms pulled it apart. It was a really good receiving antenna, so I plan to make a new one with more sturdy materials, so it can survive the harsh winter weather on an island on the west coast of Norway.
The "squished SULA" (the rectangular loop) may be a good candidate for harsh weather conditions, if built using a pipe (see the images I posted) it will offer very small surface to wind so may possibly survive those winter storms (notice, the pic at the link below is not up to scale, the support between the antenna and the mast may be as short as say 20...30cm)

viewtopic.php?p=960#p960

anyway, I'm really interested in knowing how well the "squished SULA" nulls out stations so, if possible, rotating it to "null out" a station and reporting results will be really useful and interesting
Egil - LA2PJ
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Re: Another directional RX loop

Post by Egil - LA2PJ »

Andrew (grayhat) wrote: Wed May 15, 2024 3:46 pm
anyway, I'm really interested in knowing how well the "squished SULA" nulls out stations so, if possible, rotating it to "null out" a station and reporting results will be really useful and interesting
That is exactly what I also have been thinking. But right now I'm recovering after beeing hit and severly injured by a car at a pedestrians crossing.
So at the moment I have some mobility problems and have to use a walker or crutches. The doctor indicate another six to eight weeks before I'm back to normal, so to kill a rather boring time, I'm studying how to make my antennas "weather resistant".

The original SULA was a rather good receiving antenna the few weeks it survived. But the squashed version pinned to the inside loft, using the same balun and preamplifier in my opinion worked very similar to the original. So my plan when I am back to normal is to make one of each of the antennas and try to compare them. I already have an extra balun and have ordered an extra preamplifier.
And I think your idea using a wide pipe to support the squashed antenna is very good.
It will take some time, but I'll report here when I'm back on my feet and able to play properly with these antennas. So now you know why I had to make the antenna inside the house. Must admit that this is fun!
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Andrew (grayhat)
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Re: Another directional RX loop

Post by Andrew (grayhat) »

OMG, hope you'll get better soon !!

As for the antennas, I believe that the "pipe" may be able to survive harsh weather better than the SULA, if you look at the image, you'll notice that everything is enclosed/protected by the pipe, including the coax connector, and then the pipe is small enough (assuming the original sizes are used) to stand to winds w/o issues, plus given the geometry, it's possible to use a lightweight antenna rotator to aim it

A note, since you currently have the antenna aimed at a fixed spot, if you want, you may find a station which is "at the back" of the antenna using the wire antenna or the whip of the receiver, and then with such a station tuned, use the small loop to check if the signal disappears or is strongly attenuated (as it should be)
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