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Re: LF: Re: Clipping or blanking/9kHz intermods

To: [email protected]
Subject: Re: LF: Re: Clipping or blanking/9kHz intermods
From: Stefan Schäfer <[email protected]>
Date: Sat, 22 May 2010 12:37:29 +0200
In-reply-to: <[email protected]>
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Hello Peter, VLF,

Am 22.05.2010 11:33, schrieb pws:
Stefan,

you are observing well known sunrise/-set effects and your monitor works
fine now.

I rather think that the amplifiers gain is now much more a function of the temperature. That was my worry as i saw this strong QRN decrease yesterday in the evening. It appers just when the sun is going down or coming up, so not QRN caused but sun-caused :-( Thus i installed my VFO (yesterday night) to produce a signal trace on the 2nd grabber out of 25m distance. The "ERP" was always the same but you can see QSB on the signal (some 10 dB!). That must be due to a changing working point of the amplifier and can only be temperature caused i assume, grrrrr! Maybe it is due to the source resistor of the 1st stage (before applying that, the source was directly soldered on the metallic hausing) but normally it should work even better since now the FET is rather thermal decoupled from the housing and so the influence of the sunlight should be smaller!?? And, can anyone explain where the difference of the trace of my transmitted signal in the 600 windows comes from? It is mystery for me! The transmitter was ON the whole time at stable frequency (visible on grabber 1) but on grabber 2 is looks as it would be partly OFF between 7 and 8 UTC while the background QRM hasn't changed!?? Even the 2 lines in the 600 windows of grabber2 (one with clipper, the other one with blanker) are very different to that time!?? Very complex... The poor gate of the first stage! It has to handle so many signals at very high strange there... ;-)

Aah, i have another idea: Maybe the strong QSB (even of my small transmitted signal) in grabber 2 is caused by a bad contact of the lightning arrester!? Maybe this mechanical contact is a function of the temperature and thus of the sunlight!? There appeared a IM on 18 kHz yesterday the first time. Maybe there is something like a contact in the lightning arrester that has a effect of a rectifier....
Yes, very complex but much to learn with this stuff! :-)

Wish you a nice weekend!

73, DK7FC

PS: Have to shut down the grabber 2 over the weekend...



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