fgrosz@otiengineering.com said:

What do the local TV stations use for a frequency reference?

Are there low cost receivers that also produce a good reference frequency?

--
These are my opinions.  I hate spam.

Hi

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 ….

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”.

Bob

It might of been fairly easy to use an old NTSC television signal as a
frequency reference (lumina, chroma or audio carriers). Now that it is
converted over to ATSC it would be much more difficult to recover a
reference frequency using readily available electronics.

You would have a much better chance of locking on to a commercial FM
carrier (88-108 MHz). Some are quite accurate with less than 0.5 Hz of
error.

If you want both time and frequency then a GPS source is your best bet. You
can get something like a ebay surplus Trimble Thunderbolt for less than
$150.

Tisha Hayes, AA4HA

Ms. Tisha Hayes

On Fri, Mar 30, 2018 at 5:13 PM, Hal Murray hmurray@megapathdsl.net wrote:

On 3/30/18 5:52 PM, Bob kb8tq wrote:

And Crazy Bob can convince the owner of the station that it's needed<grin>

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.

Hello to the group.
Been staying clear of the thread as many good comments.
Several things happened that made the color burst signal useless for most
people.
Yes the networks had Cesium's about 3 of them at CBS and the network feed
carried that quality.
but about 1980 a device called a frame synchronizer became popular. $25,000
each. This essentially locked the video to the local house reference.
Generally a free running ovenized crystal. At that point what was sent over
the air had no relationship to the network reference. The benefit of this
device is it allowed glitch-less switching between network and local feeds.
(Staying clear of a gen-lock discussion and terrestrial network microwave
links.)
It was the CBS network color burst that I tinkered with in 1990 to
ultimately see the satellite doppler shift on the CBS signal and other
effects.
Bad news it sort started me on the time-nuttery path and drugs like HP 5360
counters interfaced to computers.
Today the modern mpeg/atsc has none of these qualities and really doesn't
need it. Frame buffers exist in every TV. (Amazing) Originally I thought
ATSC might have value.
Regards
Paul
WB8TSL

On Fri, Mar 30, 2018 at 8:52 PM, Bob kb8tq kb8tq@n1k.org wrote:

Am 31.03.2018 um 00:13 schrieb Hal Murray:

The German channel ZDF was known to have their line frequency
derived from a Rubidium, when received from the air.
But already on cable, there might have been elastic buffers.

Now with sat and terrestrial TV gone digital, there is no such
thing as a line frequency in the MPEG data stream.
You are 30 years too late  ;-)

But you can find the pseudo noise of the satellite's own
navigation loops abt. 20 dB below the MPEG.
If you know the polynomial, you are back in time nuts land.

The 20 dB are enough that there is no interference. I wonder
how many secret services are parasites on the commercial
TV transponders. The power required for 1 Kbit/sec of
stealth transfer should be much, much lower. Even less when
you just want to disseminate a new key, with the mass transfers
done somewhere else.  Nobody would notice that. Just use
your own polynomial. With a dish on  every house that already
points to the right direction, you just need a modded feed unit.
If that is not tempting!

regards, Gerhard