[time-nuts] AM Broadcast stations as a frequency reference...

[Charles P. Steinmetz]

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