On Mon, 7 Sep 2009 07:33:01 -0400, Olin Lathrop wrote:

> It used to be you could use the TV color carrier from any of the major
> networks as a reference.  I don't know where the color carrier comes from
> for any of the remaining NTSC signals.  The networks had accurate time
> references for producing the color carriers, and routinely compared them
> against the NIST standard.  They would regularly publish the offsets so that
> measurements using their color carrier were traceable, although you had to
> wait until the offsets were published to do the actual tracing.  There were
> even some commercial frequency measuring products based on this.

I was going to suggest this sort of thing; I recently bought some bits to
build the 'Poor Man's Caesium Clock' from a Radcom (I think ?) article - a
google search will bring up the one I'm thinking of.  The project is going to
be a frequency standard and counter.

The circuit is basically an LM1880, PLL and VCO.  I can't vouch for it
though - I haven't knocked it up properly yet, but the article reckons 1 part
in 10^8 was the measured stability.  And allegedly you can even run it off-air
by using a VCR.  But you still need to figure out which stations sync to an
atomic standard, otherwise it's obviously no use.

And for some reason the BBC News 24 channel seems to send out sync pulses at
random intervals - maybe something to do with all their graphics overlays...?

Regards,

Pete Restall
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