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Date: Mon, 28 Dec 2009 16:07:06 +0100
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Thread-Topic: AW: LF: Influence of a TX antenna to a small rx antenna
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From: =?iso-8859-1?Q?Stefan_Sch=E4fer?= <schaefer@hst.tu-darmstadt.de>
To: <rsgb_lf_group@blacksheep.org>
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Subject: AW: AW: LF: Influence of a TX antenna to a small rx antenna
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Reply-To: rsgb_lf_group@blacksheep.org


Hi Rik!
Tnx for your explanations. So, perhaps my RX SNR could even be increased=
 by more attenuation, that would be fine.
I thought the most of us using a separate RX antenna, like the PA0RDT desi=
gn or a receiving loop. But now it sounds, that some are using the TX ant?=
=20
Another question: If you say that there has just to be a little difference=
 in the noise between connected and disconnected antenna, I think you mean=
, that the difference has to be as small as possible? Because, the case th=
at there is a difference, occurs at all attenuation levels from 0 dB to a=
 maximum, say 60db. So 0 dB would also fulfill this statement, of course.=
 But if the difference should be as small as possible, what about the inte=
rnal noise of the RX system? Is the part of this internal noise in that ca=
se not to much relevant? Or in other words, doesn't it decrease the SNR,=
 if the part of the received signal is small compared to the RX-internal=
 noise? I thought, the level of the received signal should be as HIGH as=
 possible, so that the input stage is just not overdriven!?

73, Stefan/DK7FC

-----Urspr=FCngliche Nachricht-----
Von: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacks=
heep.org] Im Auftrag von Rik Strobbe
Gesendet: Montag, 28. Dezember 2009 15:23
An: rsgb_lf_group@blacksheep.org
Betreff: Re: AW: LF: Influence of a TX antenna to a small rx antenna

Hello Stefan,

there is a easy way to check if you have too much attenuation or not:
Tune the RX to an unused freq (only noise/QRN) and disconnect the =20
antenna; if you can hear the difference between antenna / no antenna =20
then attenuation is not too much.
With a 11m high / 25m long lazy-L antenna at a quiet location I could =20
add 40dB attenuation and still hear the noise increasing when =20
connecting the antenna.
I guess with a kite-antenna 50 to 60dB might be a good value.
Of course it all depends also on the RX used, I use a Kenwood TS440 =20
that seems to be sensitive at LF.

73, Rik  ON7YD - OR7T