In article ,
Doug Smith W9WI wrote:
Mark Zenier wrote:
SAP is a narrowband FM subcarrier on the TV Audio Signal. 75 Khz,
I think.

78.67KHz, 5 times horizontal sweep. It's DBX companded.

The other subcarrier ("pro channel") is at 102.27KHz. It has no fixed
purpose but many stations indeed use it for studio=remote purposes.

This is the same as a SCA signal on a FM Audio Broadcast, where
67, 75, and 92 kHz are used for "Elevator Music", talking newspapers
for the blind, and various subscription ethnic radio services.

There's no 75KHz subcarrier for FM but there is a data carrier at 57KHz
on some stations, used for RDS. (which allows some newer car radios to
display the name of the station you're tuned to - and sometimes, the
song being played)

No, I've monitored some of the local SCA services here, and (as of a dozen
years ago, when I built an SCA demodulator) they did use 75 kHz. If they
bothered to have one, they usually had all three in use. There's no
regulation beyond how much modulation and bandwidth of their signal is
devoted to SCA. There's also a whole zoo full of digital services.

Mark Zenier Washington State resident