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Message-ID: <85763.34251.qm@web86501.mail.ird.yahoo.com>
Date: Sat, 20 Feb 2010 23:32:21 +0000 (GMT)
From: ALAN MELIA <alan.melia@btinternet.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: My first tests below 9 kHz
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Hi Horst dont forget you are in the near field at that frequency and the=
 signal strength drops of as the third or fourth power of the distance (no=
t the square) until you are about 15km away from the transmitter then you=
 enter the far field and get square-law effect. You need to factor that in=
to your equations. This means at 1km the strength will be either 30 or 40d=
B lower not just 20dB (I think) at 10km 60 to 80dB lower. You are really=
 in "induction" fields at the moment, I think.

Interesting tests. Make a bridge and measure the antenna at the at frequen=
cy, the majority of the resistive component will be ground loss. Tune out=
 the reactive part with inductance and use a transformer to get the highes=
t antenna current. A "ground dipole" could well be better than an elevated=
 small T.

Interesting reference
"ELF Communications antennas" Michael L Burrows, pub by Peter Perigrinus=
 for the IEE 1978   ISBN 0 906048 00 1

Alan G3NYK
=20

--- On Sat, 20/2/10, Horst St=F6cker <horst.stoecker@web.de> wrote:

> From: Horst St=F6cker <horst.stoecker@web.de>
> Subject: LF: My first tests below 9 kHz
> To: rsgb_lf_group@blacksheep.org
> Date: Saturday, 20 February, 2010, 16:39
> Hello,
>=20
> some years before, some experimental licences for ham radio
> below 9 kHz were issued in germany. Meanwhile this frequency
> range is free as the Bundesnetzagentur has confirmed last
> year.
>=20
> Transmitter is an Pr=E4citronic GF62 Level Generator
> actually at 8,79 kHz. PA is an old homebrew NF-Amplifier
> with 2x 2N3055 and about 40 Watt at 4 Ohm into a 100V ELA
> transformer. Antenna is a T-Antenne of 10m with 20m top
> capacity and poor ground.
>=20
> Receiver is a portable sferics RX that I built some years
> before (AATIS). Unfortunately its whip antenne is highly
> influenced by trees and houses.
>=20
> The fact that I can hear (!) my beacon in normal CW up to
> 100m in an city environment with a highly unmatched antenna
> makes me believe, that in a better environment and with a
> matched antenne and with help of ARGO one can make tests
> over longer distances. But even from my QTH in the city the
> ODX ;-)) surely can be improved.
>=20
> The mean problem now ist how to match the antenna . . . -
> or using ground antennas vor TX, RX or both.
>=20
> vy73 Horst
> ___________________________________________________________
> NEU: Mit WEB.DE DSL =FCber 1000,- =BF sparen!
> http://produkte.web.de/go/02/
>=20
>=20