Yep Ive just been discussed this with John TAG trying to recall what we have did- as ever my files are back in Alaska and Im here..
I did "try" 2T (the loop was 4 large conductors in parallel separated between metres on the vertical and top horizontal sections and about 5 Cms on the lower horizontals) - the results did not give an improvement in far field or local mobile field measurements, but, I did not fully investigate the other losses - my total loop current did decrease, and other losses would indicate that this negated any "gain" perceived or otherwise...
Ive been racking my brains and as far as I can remember a single turn I realized around 49A loop current and 2T around 33A fully matched using the "M0BMU scopematch" for around 1Kw into the loop.
Im sure there is more...
Laurence in BY3A
> From: [email protected]
> To: [email protected]
> Date: Mon, 23 Nov 2009 01:09:24 +0000
> Subject: LF: Re: N-turn TX Loop
>
> Hi Piotr I think Laurence KL1X had 2 turns in Oklahoma.(about 100m
> periphery)
> I think there are other loss problems as you increase the turns. Jim M0BMU
> is the expert on that.
>
> Alan G3NYK
>
> ----- Original Message -----
> From: "Piotr Młynarski" <[email protected]>
> To: <[email protected]>
> Sent: Monday, November 23, 2009 12:19 AM
> Subject: LF: N-turn TX Loop
>
>
> > Dear LF group,
> > I would like to put for your consideration the issue of
> > multi-turn transmitting loops. Have you ever done such an experiment on
> > LF ?
> > This sunday evening i decided to do some simple math and it turns out
> > that such a N-turn TX loop should work ( at least on the paper)
> > The radiation resistance is proportional to the square of so called
> > "effective
> > height" and this last term can be easily derived for a loop i.e. it is
> > equal to
> > 2*pi*A*N/lambda where A denotes area closed by a loop a N is the number
> > of turns
> > so the radiation resistance for a single turn loop reads as
> > 320*pi^4*A^2/lambda^4
> > For the N-turns the radiation resistance obtained for a single turn is
> > multiplied
> > by N^2. Ok, the R (ac) is increased as we increase N but this is linear
> > with respect to N
> > and therefore we should have gain in the radiated power.
> > (there is an implicit assumption made: the loop is "small" i.e. the
> > current is constant)
> >
> > i did some calculations: assumed TX power ( and later, perfect match to
> > the loop) 200 Watt
> > environmental loss: 1.5 Ohm, diameter of the wire d = 3 mm, rectangular
> > shape of the loop
> > i.e 10 meters by 20 meters ( less optimal than square or circle )
> > so A = 200 sq.m For N =1 (classical tx loop) we get R(AC) = 0.62 Ohm
> > ( Rac formula taken from ARRL Antenna Handbook, f = 137.7kHz)
> > radiation resistance RRAD = 55.5 microOhm, total R loss = 2.12 Ohm,
> > efficiency is 0.0026% and radiated pwr 5.2 miliWatts, I = 9.7 Amp.
> > Next, I took N =3 so the wire length is changed from 60 meters to 180,
> > everything else was kept the same and now one gets: R(ac)= 1.85 Ohm so
> > R loss = 3.35 Ohm
> > RRAD = 499.5 microOhm, efficiency increased to 0.015% and radiated pwr
> > abt 30 miliWatt, I=7.7 Amp
> > I am sorry bothering you but i simply would like to learn
> > where is the 'catch' here - if there is one ...
> > I guess the assumed loop i.e. 10 by 20 mters is 'reasonable' as TX antenna
> > i took these values after reading the article about
> > WD2XES first TX loop: 40 feet by 65 feet - well , almost the same
> > dimensions.. :)
> > From practical reasons the N values will likely be small , say, 2 or 3
> > but as the above numbers show maybe it is worth doing it.
> >
> > 73 de Piotr, sq7mpj
> > qth: Lodz /jo91rs/
> >
>
>
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