From: "Mike Dennison" <mike.dennison@ntlworld.com>
To: rsgb_lf_group@blacksheep.org
Date: Sat, 19 Mar 2011 13:11:47 -0000
MIME-Version: 1.0
Message-ID: <4D84AB93.27977.CC1BE4@mike.dennison.ntlworld.com>
In-reply-to: <000e01cbe589$d2324060$0401a8c0@xphd97xgq27nyf>
References: <AANLkTi=j-Bp7+YC+527yQ6EBahLUdq6WqYXSGNTk33m7@mail.gmail.com>, <000e01cbe589$d2324060$0401a8c0@xphd97xgq27nyf>
Content-description: Mail message body
Subject: LF: Re: Loop TX antennas at VLF?
Content-type: text/plain; charset=US-ASCII
Content-transfer-encoding: 7BIT
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


In fact, several people used loops successfully on 73kHz, and some 
distance records were achieved using these antennas. 

My own experience was that a loop was as good as a vertical but only 
in its best direction. The directivity of the loop reduced the number 
of possible stations to work, so that's why I eventually opted for a 
vertical..

Mike, G3XDV
==========

> 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
> >
> >
> 
>