That's the most compelling argument I've seen to explain this...when Ron mentioned
that the modulation was in the Q channel, you had to know that it wasn't coming from
conventional amplitude modulation.

The only other explanation I can come up with, building on this one, is that this
transmitter's exciter has developed a phase-modulated hum. Keeping in mind that all
transmitters have exciters which operate from low voltage power supplies, and those
supplies are usually powered with single-phase 120 VAC, a 'lytic that went south
could possibly explain it without having to resort to an abandoned but still
connected stereo exciter. You wouldn't hear the hum, as already established, if you
were dead-on tuned, since the RF exciter's amplitude, even if it was affected by the
problem, is clipped by the next class C stage the RF path encounters, but you'd see
the sidebands in a spectrum analyzer, and you could hear all but the quietest of
these when you tuned through the center.

If I were the engineer in charge, I'd be embarrassed to have to admit the latter, but
probably even more embarassed to admit that maintenance on the rig was so bad that
this situation could occur. After all, it's detectable with a simple
tune-through...is this to say that the station's engineers NEVER tune into the
station? When I ran a transmitter plant, it was an expected job function to LISTEN
to the station for frequent quality checks, even if it wasn't the preferred format
for the engineer. And from WBRW says, this was mentioned to the CE a long time
ago....if he was doing his job, he'd have looked into it. I couild understand if
this was a 1kW daytimer, but this is a Class I Clear, after all. And what
quasi-natural interference, in anyone's experience, isn't amplitude modulated?

And they say that deregulation is good for broadcasting!
--
For direct replies, take out the contents between the hyphens. -Really!-


"WBRW" wrote in message
om...
Since Thursday morning I've been hearing 120Hz hum on WFAN (NYC) 660,
does anybody else?

I've been hearing a background hum on WFAN for a LONG time, but only
when listening in "forced" AM Stereo. When listening in mono, the hum
disappears.
[...]
I once asked WFAN's engineer about this hum, and they said WFAN was
not transmitting it, and that it was being caused by my reception
conditions, such as electrical interference. However, I hear this hum
from WFAN, and ONLY from WFAN, 24 hours a day, even when there's a
local power failure and thus no electrical interference can possibly
be generated!

WFAN _was_ an AM Stereo station until about two years ago, when they
reverted to mono. But, it IS possible that their C-Quam AM Stereo
exciter is still installed and operational, but merely is being fed
with mono audio and has its 25 Hz pilot tone generator switched off --
which, for all intensive purposes, means WFAN is transmitting a
conventional "mono" signal. However, if that AM Stereo exciter ITSELF
is the causing this 120 Hz hum, it could be introducing it into WFAN's
signal in the manner that I described -- only "forced" AM Stereo
listeners will be able to hear it, while mono listeners won't hear the
hum.
[...]