This is true , I contract for quiet a few AMs and FMs that can't
find anyone that want to be on 24/7 call. There is this "thing"
called FCC Yearly NRSC Tests where an engineer with an analyzer checks
the spectrum and the station(s) must meet spectral purity ... ie: no
spurious emissions higher than XX db removed yy Kc from carrier. It
sounds like one or both stations are producing an unwanted mixing
product. "IF" they are co-located on or at the same site, the
combiner "should" include traps that filter or reject each other's RF.
It's possible that lightning / age / rats / snakes / birds have changed
the inductance of one of the traps.
So, both of the stations may be unaware of the interference except on
the day of the NRSC test.
Don W4DNR
Jim VE&RF said :
Problem is most AM / FM stations these days all contract out the work
for regular maintenance.
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