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 design or
a receiving loop. But now it sounds, that some are using the TX ant?
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 that 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 internal noise of the
RX system? Is the part of this internal noise in that case 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
-----Ursprüngliche Nachricht-----
Von: [email protected]
[mailto:[email protected]] Im Auftrag von Rik Strobbe
Gesendet: Montag, 28. Dezember 2009 15:23
An: [email protected]
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
antenna; if you can hear the difference between antenna / no antenna
then attenuation is not too much.
With a 11m high / 25m long lazy-L antenna at a quiet location I could
add 40dB attenuation and still hear the noise increasing when
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
that seems to be sensitive at LF.
73, Rik ON7YD - OR7T
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