Re: [Amps] OFF TOPIC: Loop antenna question

[Alek Petkovic <vk6apk@eon.net.au>]

Have you thought of a section of open wire line in the feedline at the feed 
point which puts the equivalent amount of wire into the loop to resonate it 
on 75m?

eg: a 75m loop for 3.9MHz is around 258' and for 7.2 MHz it would be 140'. 
That is a difference of 118'. If you were to use a 59' section of open 
wire, it would put 118' of extra wire into the loop.

If it is not possible to do it that way, you could perhaps put one or more 
loading stubs, say at the support points, still using open wire, to make 
the antenna up to the total required length.

I have not tried this but it could be a cheap solution and well worth some 
experimentation.

Good luck,
Alek. VK6APK

ps:
I hope to be making a nuisance of myself on 75m over the next week from my 
beach house using my 2 x 3-500z and Carolina Windom 80. Watch out for me. 
I'm heading down there tomorrow.




At 12:53 PM 26/12/2004, JimMoci@aol.com wrote:
> Happy holidays to all on the amps reflector. I have an off topic question
> about a loop antenna so if it is not appropriate please remove it or 
> respond to
> me directly via email. I am asking here because there are so many experienced
> and knowledgeable people on this reflector and the info I receive will be 
> very
> useful.
>
> My situation: I currently have a full sized 40 meter delta loop @ 30 ft and
> it is horizontal to the ground. I use it on 40 thru 10 with good results. The
> antenna exhibits a good SWR on 40 and an SWR less than 2.5:1 on 20 thru 10
> meters so the internal auto antenna tuner in my Icom solid state amp can 
> handle
> the mismatch. What I would like to do is use it on 75 meters but dont have 
> the
> room for a full sized 75mtr loop. The loop is to small for 75 and has an very
> high SWR, to much for the internal tuner to deal with. So far I have tried
> splitting it in the middle, essentially a full sized 75 meter dipole 
> folded back
> on itself. It works ok, but not a stellar performer. It also lost the 
> advantage
> of being a quiet receiving antenna, a characteristic loops are known for.
>
> I have a couple ideas that I want to try but figured I would ask before I go
> climbing tress out in the cold. The first idea was to add another full 
> turn to
> the loop, separated by a few inches. Essentially it would be a 2 turn loop,
> totalling about 260 feet, but only taking up the space of a 40 meter loop. 
> The
> other idea was to add a large inductor in the middle of the loop. I have a
> large, silver plated, flat wound inductor from a broadcast transmitter 
> that would
> do nicely. I also have a vacuum relay that I could use to short it out for 40
> thru 10 mtrs.
>
> My main question is will the two turn loop work? If so will it be better than
> the inductor?
>
> I realize that I could use a large roller inductor tuner in the shack but
> that defeats the purpose of my lazy hams push button station. My solid state
> kilowatt is silent and automatic and it is my goal to keep the station 
> totally
> push button.
>
> Thanks for any and all advice- It will save me many trips up the tree and
> there is snow in the forecast. Why didnt I do this in the summer?!?!?!
>
> 73,
> Jim W3ATV
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