Just a final update on the 19kHz FM stereo pilot tone (compared to TV sync).
If you are not interested in this subject, please stop reading here or click
on the delay button of your Email browser. Or explain to me why if it is
completely "off-topic"... ( IMHO it's just a very little "off-topic" ;-)
The stereo pilot tone used by FM broadcast stations is quite accurate for the
large FM stations, and some may be useful for us as a cheap frequency
reference, BUT (as Alberto 'PHD already thought):
You have to find a station which produces an accurate frequency.
In north western DL, I could not even find two with exactly the same pilot
frequency.
Just a few samples (without "absolute" accuracy, just to show the difference:
WDR1: 19000.00 Hz (I used this as a pseudo-reference for the soundcard)
WDR2: 19000.27 Hz (same company, other transmitter, 14 ppm off ?! )
WDR4: 19000.12 Hz (...)
BFBS: 19000.07 Hz (British Forces Broadcasting Service)
Maybe BFBS uses the the same stereo pilot tone as the BBC in London. WDR is
one of the largest broadcasting companies in DL, but even they seem to differ
from each other. (Compared to the accuracy of some well-equipped 'big guns'
on LF, one may say the commercial broadcasters have lousy accuracy ).
To verify that these differences are not propagation effects, I also compared
some the TV line frequences (using a soundcard at 44100samp/sec, mixed down,
decimated by 81, 64k FFT size, 0.008Hz resolution). All TV stations were
received 'old style' via antenna.
The TV line synch frequencies found this way (using the same "correction
factor as above):
ARD: 15625.18 Hz
ZDF: 15625.19 Hz
WDR: 15626.18 Hz
RTL: 15626.20 Hz
The difference between these signals are still above 1ppm (!?), but this may
be based on propagation effects (It's not the measurement, I verified by
switched the stations and watching the effect on the waterfall).
Hope to meet you on the band in regular CW next weekend, even if it is our
10th QSO !
73's Wolf (DL4YHF, DF0WD)
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