[BC] Transmission vs received bandwidth

[Phil Alexander]

On 19 Jul 2006 at 22:07, stanleybadams wrote:

 > Sometimes the 680 site (original WMPS) has IBOC on at night, perhaps
 > testing, but if you want to listen to WLW at 700 and a Cincinnati Reds game,
 > forget it.
 >
 > That is the only transgressor that I have heard around here.  But the 1030
 > Spanish station has birdies all over the place at times.
 >
 > OBTW, all I can say is Praise God for small favors.  WCKY, 1530 is rid of
 > Air America, at least at night, it is now a sports station.  Wish the oldies
 > would return but anything is better than AIR AMERICA, how bout them apples
 > you NE liberals you (not wanting to fan the flames too much.)

Stan,

There are not *supposed* to be IBOC emissions beyond +/- 15 kHz. If they
are present there is a non-linearity in either the transmitting antenna
system or the receiver front end, or the receiver has a good I/F IOW
 > +/- 5 kHz bandwidth. If a station has dynamic pre-distortion in the
PA, the "bumps" in the spectrum should be only slightly above the noise
floor, or about -87 or -90 dBc. On a communications receiver with a
clean antenna, the I/F set to narrow band and RF gain backed off to
prevent overloading you should be able to copy WLW when 680 is fired up.
If not, 680 may have a mis-match with some VSWR, but I'd be reluctant
to find them guilty without a standard mask measurement in hand.

Not that it makes much difference to the listener, but I suspect we will
find second adjacent IX more related to the set than to the Tx plant.
If only that were true of the first adjacents. Sadly, that is a whole
different problem.


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Phil Alexander, CSRE, AMD