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Re: LF: RE: Loop Conundrum

To: [email protected]
Subject: Re: LF: RE: Loop Conundrum
From: "Warren Ziegler" <[email protected]>
Date: Mon, 21 Jul 2008 11:47:13 -0400
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Mitch,

      The vhf antennas are full wave loops with a relatively high
radiation resistance and low loss, electrically small loops at LF are
the opposite, i.e. low radiation resistance and high loss.

73 Warren K2ORS


On Mon, Jul 21, 2008 at 11:34 AM, Mitch Buchman <[email protected]> wrote:
> How is this different from an eggbeater or turnstile antenna, that is
> often used at VHF?
>
> http://pagesperso-orange.fr/on6wg/Doc/Antenne%20Eggbeater-Engl-Part1-Full.pdf
>
> and
> ARRL Radio Amateur Satellite Handbook 1st ed, p10-16
>
> Mitch
> KB3MYC
>
> On Mon, Jul 21, 2008 at 8:02 AM, Gary - G4WGT <[email protected]> wrote:
>> Andy, LF,
>>
>> You wrote :-
>>
>> "Now, I take two identical such loops and mount then on the same centre line
>> but at right angles to each other so there should be no coupling
>> between them, whatsoever.   Now, I connect the two loops in series and
>> resonate the combination with a single capacitor of half the original
>> value."
>>
>> I have been pondering about something similar as I have problems remotely
>> rotating yet another antenna.
>>
>> My idea is to make the loops in the same way as you describe but feed the 2
>> loops to the two inputs of a balanced pre-amp like the G3LNP loop pre-amp
>> shown in the "LF Experimenters Handbook"
>>
>> What are your thoughts on that please.
>>
>> Gary - G4WGT.
>>
>> -----Original Message-----
>> From: [email protected]
>> [mailto:[email protected]] On Behalf Of Andy Talbot
>> Sent: 21 July 2008 12:30
>> To: [email protected]
>> Subject: LF: Loop Conundrum
>>
>> Was pondering this while out walking the other day, and couldn't come
>> to a satisfactory conclusion either way...
>>
>> A small magnetic loop mounted vertically has a defined radiation
>> resistance that is a function of its diameter, a loss that is function
>> of its conductor and hence a loss or efficiency that is the ratio of
>> the two. It is resonated with a good quality vacuum capacitor, and
>> fed/matched by any suitable metrhod.  Lets also leave aside all the
>> myth and folklore about small loops, and also ignore the environment
>> for now.   It also as a radiation pattern with nulls.
>>
>> Now, I take two identical such loops and mount then on the same centre
>> line but at right angles to eachother so there should be no coupling
>> between them, whatsoever.   Now, I connect the two loops in series and
>> resonate the combination with a single capacitor of half the original
>> value.   The resulting radiation pattern should have the nulls filled
>> in, and be a reasonable approximation to omnidirectional in azimuth.
>>
>> BUT...
>> What is the resulting change in efficiency?
>>
>> Argument 1:
>> Two identical loops = two times the loss R,  but also two times the
>> radiation resistance (since they don't couple) so net efficiency
>> remains the same.
>>
>> Argument 2 :
>> Chu-Harrington relates efficiency / Q / bandwidth / volume enclosed.
>> Therefore, as the enclosed volume has increased, the effciency ought
>> to rise.
>>
>> Both arguments developed little side trendrils & thoughts as I walked
>> and pondered, and both appear valid in their own way.  So
>> the floor is open for discussion :-
>>
>> And where does the net radiation pattern fit into the equation?  Does
>> it, at all ?
>> --
>> Andy G4JNT
>> www.scrbg.org/g4jnt
>>
>> ps.  Fascinating paper on EMP btw. - I was up way past midnight last
>> night  reading it.
>>
>>
>>
>
>



-- 
73 Warren K2ORS
 WD2XGJ
 WD2XSH/23
 WE2XEB/2
 WE2XGR/1


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