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Date: Tue, 29 Dec 2009 04:34:13 +0100
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Thread-Topic: AW: 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: AW: LF: Influence of a TX antenna to a small rx antenna
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Reply-To: rsgb_lf_group@blacksheep.org


Rik, tnx very much. I will test it and am curious about that!
That would of course be even the easiest solution for the RX.
In 08/2001, Rudi/DJ2EY has published a bandpass filter (4 LC Filters, loos=
e capacitive coupled) in the CQDL. I already thought about building such=
 one. If one is choosing an attenuation so that the Ls will not be overdri=
ven, that could give a fine SNR, better than with a attenuator that even=
 filters the wanted spectrum?
73, Stefan
-----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 17:50
An: rsgb_lf_group@blacksheep.org
Betreff: Re: AW: AW: LF: Influence of a TX antenna to a small rx antenna

Hello Stefan,

the problem with "big" antennas for RX is that they overload the =20
receiver and cause IMD effects. Most harmfull is 3rd order IMD and the =20
good thing with an attenuator between antenna and RX is that for every =20
dB attenuation the 3rd order IMD is reduced by 3dB. Therfor you may =20
want to increase attenuation as long as the external noise level is a =20
bit stronger (let's say 3 to 6dB) than the internal (RX) noise level.
As long as this is the case the attenuator will not affect the overal =20
RX sensivitity (although you will get little or no s-meter reading), =20
but IMD behaviour will improve by 100dB or more.

73, Rik  ON7YD - OR7T