On 3/30/18 5:52 PM, Bob kb8tq wrote:
Hi
On Mar 30, 2018, at 6:13 PM, Hal Murray <[email protected]> wrote:
[email protected] said:
Now that analog TV has gone away, so
have these signals.
What do the local TV stations use for a frequency reference?
Anything from a crystal oscillator to a Cs standard. It’s very much a “that
depends”
sort of thing. If Crazy Bob is the chief engineer it might be a hydrogen maser
….
And Crazy Bob can convince the owner of the station that it's needed<grin>
Are there low cost receivers that also produce a good reference frequency?
As noted earlier, color burst references were a big deal a long time ago.
Depending
on how they do what they do it might still be a good bet. The big risk is that
it could
be a good bet “most of the time”.
I wonder how stable the underlying timing of ATSC or DVB-T is? You
could recover the carrier or bit clock from an over the air signal,
should you be lucky enough to live where the signal exists. It's non
trivial - all modern receivers do it as part of a single cheap
monolithic chip - but maybe you could find some SDR code to run on a
PLUTO or other cheap SDR that lets you "see" that level of the signal.
There's no inherent reason why it should be controlled well, at least
for ATSC - the receivers are designed to tolerate multipath, Doppler,
and other impairments.
But for simulcasting, the various transmitter carriers need to be
matched fairly well.
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