Burt wrote:
There are some AM broadcast stations in the U.S. that are GPS referenced.
Supposedly being GPS locked would allow receivers that are GPS
locked to lock up faster and stay locked better. So far I don't
know of a single IBOC receiver that has the capability of being GPS referenced
while it would be simple enough to GPS lock/reference an AM
broadcast transmitter, this may not always be desirable. Having two
co-channeled stations precisely on or very near the same frequency,
even though they may be thousands of miles apart, can have serious
fade issues. If they are exactly on the same frequency they can
cause deep nulls in their coverage depending on the relative signal strengths.
I believe the argument that was advanced for better reception through
GPS-locking had to do with improving nighttime skywave reception. So
the argument went, locking the carriers of co-frequency stations
would prevent fast fading (beating). Instead, you would get only
long fades due to atmospheric changes. I'm not sure how much of an
advantage that would be, in practice, but it shouldn't mess up local
coverage (which is all the FCC cares about).
Best regards,
Charles
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