Hello Jim,
What a surprise, i didn't expect such a story as a result of my
spontaneous transmission ;-)
Congrats to your compact and well performing antenna which will be good
for holidays and /p, if home QRM rises and rises with the years. This
should be a good solution for many QRM bothered OMs. Better to take a
walk and try it from a bank with a good view beside a forest than
sitting at home and trying for hours without success!
Yes, 136.5 kHz would be more useful for a CW QSO. We really should try
that ASAP. Are you ready for transmitting?
Ah and thanks for the nice report ;-)
73, Stefan/DK7FC
Am 28.08.2011 20:44, schrieb James Moritz:
Dear LF Group,
The QRN level on 136kHz has finally died away, and I was able to
record the attached spectrogram, showing DK7FC calling CQ around
1755utc, using my prototype ferrite rod antenna. On the left of the
spectrogram, the rod is oriented for N-S reception, and the background
noise consists mainly of horizontal Loran spectral lines, plus some
unidentified, low-level, local "mush". On the right of the
spectrogram, Stefan's signal level increases as the rod is rotated for
E-W reception. Here, the noise level is mainly vertical streaks due to
sidebands of DCF39's FSK modulation. The black area at the right hand
edge of the screenshot is where the ferrite rod was replaced by a
"dummy antenna" inductor, and shows that the internal noise level of
antenna and preamp is below the band noise level (by around 10dB).
The band noise seen with the ferrite rod is practically the same as
seen with larger loop antennas under quiet conditions, so this
practical test does show that a reasonably compact ferrite rod can
give sensitivity limited only by the external band noise on 136k. In
fact, there is some margin for making the rod smaller still in this case.
BTW, Stefan was an S4 audible signal - CW would have been a bit
difficult due to the bursts of noise from DCF39, but a QSO would
certainly be possible, especially if a quieter frequency were chosen.
Cheers, Jim Moritz
73 de M0BMU
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