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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