Message-ID: <3A7092D4.AA64C48@sitestar.net>
Date: Thu, 25 Jan 2001 15:55:48 -0500
From: "Rye Gewalt" <ryeg@sitestar.net>
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To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: RE: Final update on FM 19kHz pilot tones
References: <65AECDF1F89AD411900400508BFC869F0D7560@pdw-mail-1.dera.gov.uk>
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I think that TV stations  may also sync their signals so that when propagation is
good the interfering signals don't "roll' through one another.  I can remember in
the early days of TV here in the states that we would occasionally see such
things --- when they were not synched.  Now you just see a stable ghost of the
'interfering' station in the background. Since TV is AM, there is no appreciable
'capture effect' like on FM and a weak signal can ghost through a marginal local
signal.

Just a supposition, but I think it makes sense.   I suspect it makes even more
sense on your side of the pond where spectrum is even more highly congested.

Rye K9LCJ


Talbot Andrew wrote:

> Wolf - are you absolutely sure about the TV timebase frequencies ?   My
> understanding is that ZDF sync pulse form a national standard for time
> distribution in D Land and should be exactly 15625.000   This is borne
> out by German microwave opertors who use ZDF TV sync for high accuracy
> frequency standards and I'm told it is an inheritance from Unification
> where the DDR originally used this method of national time and frequency
> distribution.  Your measurement of 0.19 Hz high suggests a soundcard
> sampling error of 12ppm which looks feasible.
>
> I find it hard to believe that any of the TV stations would be out by
> more than 30ppm even if a cheap and nasty TTL oscillator module were
> used - which WDR and RTL evidently are.  Your measurement of ARD looks
> to be within tolerance of your quoted accuracy so the betting is those
> are the identical frequency
>
> Andy  G4JNT
>
> > 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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