[sdiy] A Frequency Standard for Poor People?

[Grant Richter]

on 12/15/03 8:49 AM, Magnus Danielson at cfmd at bredband.net wrote:

>> signals derived from color television broadcasts
> 
> Can be tricky if you are not sure about the traceability of the signal, i.e.
> if you know that it actually derives from a stable enought source. Both PAL
> and NTSC allow for single digit PPM deviations and speed of deviations can be
> quite severe.

Broadcast network channels (ABC, CBS, NBC) are NIST locked. This is so an
affiliate signal from each coast is only phase shifted and can be resynched
with just a delay line. Dates to before digital time base correctors.

All the frequencies in video are multiples of 60 Hz in US and 50 Hz in
Europe. This is so "hum bars" (power supply noise) are stable. If you see a
"hum bar" drifting slowly, it means the broadcast source is reference
locked.