Hi LowFers.
Too lazy to make quality narrow input filter I tried another thing.
I made a loop ant of a shape of square, 65cm by 65cm. Size mainly
limited by my wife's tolerance. There are two windings on it. Main is
50 turns and the latter is separate 5 turns. Used wire is insulated
copper wire diameter 0.3 mm only . The main one is tuned to
resonance by varible capacitor abt 500 pF.
Hot end is fed to gate of BF245. In collector
(drain) there is the the latter winding in series with trimmer
2200 ohm. The 'polarity' of this secondary winding must tried to
find positive feedback. By the trimmer the feedback can be
easily adjusted so that you can find a point where oscillation begins.
It you set feedback close to this point (not necessary to be
very close) the ant has following behaviour.
It tunes very sharply. It has to be retuned even within 136 kHz
band. When it is carefully tuned to a certain fq (136 kHz)
the fq 3 kHz distant (139 kHz) seems to have attenuation about
15 dB! I was surprised that the band is actually empty, full of
smooth ground noise, which is different from what I experienced before
on this band. Also, galloping horses can be clearly heard on 100 kHz.
To tell the whole story I live in a block of flats so that there is
a lot of TV sets and other appliances in vicinity.
I tried to listen several times during this wekend but I have not heard any
ham-looking signals. My QTH is Hradec Kralove which is about 100 km
east from capital Prague. Locator is JO70WE. Who is closest to me?
Is he willing to make a beacon for me for few minutes? Ones I
saw 137 kHz in DX-Cluster too, but not this weekend. Are there any
prefered times/fqs to try to listen on the band?
73! Petr, OK1FIG
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