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isw

In article ,
wrote:

"SCA sub-carriers never went above
about 80Khz, so there was no increase in occupied bandwidth. IBOC
changed all that by grabbing all the spectrum between +/-100kHz and
+/-200KHz: "

But bear in mind there were adverse implications. When it was simple "store
cast allocation" it was at 76 KHz, locked to the 19 KHz stereo pilot. The
deviation was very low and did not produce much in the way of sidebands.

SCA usage predates FM stereo. Originally there were two subcarrier
frequencies: 43 kHz and 76 kHz. As stereo broadcasting became popular,
the 43 kHz channel was abandoned due to interference. While some
broadcasters may have synchronized the 76 kHz frequency with the 19 kHz
stereo pilot, this was not required. Plus, since the SCA signal itself
is frequency modulated, locking it to the pilot would not accomplish
much in any case.

Isaac