From: WarmSpgs@aol.com
Message-ID: <a4.f3d8d81.27a4cd47@aol.com>
Date: Sat, 27 Jan 2001 20:17:59 EST
Subject: Re: LF: RE: Final update on FM 19kHz pilot tones
To: rsgb_lf_group@blacksheep.org
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In a message dated 1/25/01 4:01:41 PM Eastern Standard Time, 
ryeg@sitestar.net writes:

<< 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. >>

This may be true in some major television markets, but it is not the case 
nationwide.  Most television stations are not synched to anything but a local 
reference oscillator, usually a TCXO.  This is a big improvement over the 
situation in the 1960s and early 70s, but it is not nearly as good as that 
period in the late 70s to early 80s when all networks' atomic-referenced sync 
pulses were passed directly by local stations.  Back then, it was literally 
true that "ghost" sync bars would stand still at the same position day after 
day.  (In locations where it was possible to overlay the video from three 
stations carrying the same network program, it was great fun to try to deduce 
either the spacing between the stations or one's own position relative to 
them.)

Now, frame synchronizers re-sync incoming network signals, the output of 
videotape machines, and all other sources to the local studio reference.  The 
network owned-and-operated stations may use atomic standards or GPS-based 
references, but most others don't.  Sync drift is generally very slow, but it 
does occur in most of the country.

73,
John