[Premium-Rx] Time Signal Station Receivers sought

[David I. Emery]

On Sun, Jan 01, 2006 at 06:02:07PM -0800, John wrote:
> Hi Ed & group,
> 
> These days, networks are genlocked (synchronized) to master time/frequency 
> systems -- I've seen rubidium and GPS - disciplined systems.  This stuff 
> has become so inexpensive these days, that even local stations can go with 
> GPS locked systems.  Sync generators are so accurate that many stations 
> just run a master sync generator for their in-house use, and have frame 
> synchronizers (retiming systems) on incoming lines such as network feeds, 
> so that the network is forced (call it finessed) into time with the local 
> station. Because of this retiming, it is no longer accurate to assume that 
> frequency is "network-accurate" when airing a network show.  The signals 
> are, however, extremely accurate.

	I might add my two cents here... more and more network program
distribution is now MPEG digital (ALL of it soon will be) via satellite 
(or in a few cases leased fiber) so the days when the color burst
frequency and timing of network feeds was super accurate because it was
rubidium or cesium timed in NY or LA and fed over stable AT&T microwave
circuits to the local stations is very very long gone.

	The microwave circuits mostly were replaced by analog satellite
in the early 80s and now post millennium by completely digital MPEG
compressed transmission.   And even in the 80s when most things went via
analog satellite the accurate timing largely evaporated because - guess
what - satellites move around in their nominal orbital position boxes
significantly and this creates quite measurable doppler shifts and
accumulated timing errors.

	Today, of course all one has is an incoming stream of bits
(maybe with some course time of day information in the vertical interval
time codes) fed into a broadcast satellite IRD that likely can be and is
genlocked to the local house sync generator.   But it in turn may just
output bits (SDI/HDSDI) in time with house sync which are input into
switchers, frame store/TBCs and eventually digitally to  a SDI to NTSC
modulator somewhere near the transmitter. If the station is careful this
may be clocked by a precision GPS locked reference clock, but it
certainly doesn't have to be.   It might be just using its internal
standard...

	But when one can buy GPS disciplined frequency standards used on
Ebay for $200-400 and new for a couple of K it hardly seems useful to
base timing or frequency on anything else when a good GPS box will do
parts in 10^11 or better frequency and about 50 ns accurate time of
day... why do you need anything else ?

-- 
   Dave Emery N1PRE,  die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."