[Amps] OFF TOPIC: Loop antenna question

[R.Measures]

On Dec 26, 2004, at 12:40 AM, Alek Petkovic wrote:

> 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.
>
The wire in a balanced feedline does Not add to the wire in the antenna 
-- i. e., antennas and feedlines are not like series resistors.  .

The best antenna I have used for limited space on 80m - 160m is the 
(end-fed against gnd) Hertz.  A 100' by 60' lot will accommodate a 
fairly efficient Hertz antenna.  The tradeoff is that a 
remote-controlled  L-network is required at ground level at the driven 
end of the wire.

> 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 at 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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>
> http://www.qrz.com/vk6apk
> http://profiles.yahoo.com/vk6apk
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org