Message-ID: <000e01cbe589$d2324060$0401a8c0@xphd97xgq27nyf>
From: "mal hamilton" <g3kevmal@talktalk.net>
To: <rsgb_lf_group@blacksheep.org>
References: <AANLkTi=j-Bp7+YC+527yQ6EBahLUdq6WqYXSGNTk33m7@mail.gmail.com> <59F87B1BA5D04A2F98902CF94C38DB30@JimPC>
Date: Fri, 18 Mar 2011 16:30:40 -0000
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Subject: LF: Re: Re: Loop TX antennas at VLF?
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James es  Co
These type of loops were tried years ago on 73 khz, single turn, multi turn
and never covered the distance compared to the loaded vertical variety at
the time. All those chasing DX both on 73 and 137 all used loaded verticals
and were very successful.
One or two experimenting with loops managed only short distances, then gave
up.
de mal/g3kev

----- Original Message -----
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Friday, March 18, 2011 3:26 PM
Subject: LF: Re: Loop TX antennas at VLF?


> Dear Roger, LF Group,
>
> > Just wondering if anyone has done the maths to work out what sort of ERP
> > could be expected at 8.97kHz with, say, 100W to a smallish loop antenna
in
> > the garden?
>
> A 10m x 10m, 100m^2 loop of  "thickish" 3mm dia solid wire would have a
> resistance at 9kHz of roughly 0.1ohm. With 100W available, 32A antenna
> current should be possible, assuming negligible tuning capacitor losses.
> Inductance would be of the order of 40uH. A tuning capacitor of roughly
8uF
> would be needed.
>
> The radiation resistance of an electrically small loop is:
>
> 320 * pi^4 * A^2 / (lambda)^4, where A = area, lambda = wavelength
>
> for 100m^2 at 9kHz, Rrad is about 250 pico-ohms (!)
>
> The ERP is then 1.8 * I^2 * Rrad, about 0.45uW
>
> So pretty low, but with a bit bigger loop and a bit more power, it would
> seem to be competitive with small verticals of a similar size. This is
> perhaps mainly because of the serious losses present in loading coils that
> people have been able to make for verticals, combined with high voltage
> limitations of fairly short wire antennas, and high environmental losses
of
> various types also due to high electric fields. The voltage in this
example
> would only be about 70V. So might be worth trying for "back garden"
> experiments (assuming your antenna masts can support thick enought wire!),
> although I think it would not be competitive for bigger balloon/kite
> supported vertical antennas.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>