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 (not 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 into your equations. This
means at 1km the strength will be either 30 or 40dB 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 frequency,
the majority of the resistive component will be ground loss. Tune out the
reactive part with inductance and use a transformer to get the highest 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
--- On Sat, 20/2/10, Horst Stöcker <[email protected]> wrote:
> From: Horst Stöcker <[email protected]>
> Subject: LF: My first tests below 9 kHz
> To: [email protected]
> Date: Saturday, 20 February, 2010, 16:39
> Hello,
>
> 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.
>
> Transmitter is an Präcitronic 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.
>
> Receiver is a portable sferics RX that I built some years
> before (AATIS). Unfortunately its whip antenne is highly
> influenced by trees and houses.
>
> 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.
>
> The mean problem now ist how to match the antenna . . . -
> or using ground antennas vor TX, RX or both.
>
> vy73 Horst
> ___________________________________________________________
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>
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