[BC] Hello Craig

[Craig Healy]

> You note resonated with me.  That 3rd order issue was in the back of mind
> too when I asked a while back about the existence of any 2A +/- B mixing
> charts for AM stations (especially in large markets).  You know better
than
> I that this is an issue as regards noise floors.
>
> In IBOC, this will cause the AM noise levels to rise on non-IBOC stations,
> and the cheap little radios that are not IBOC will have a more troublesome
> time in tuning around.

The other thing that I didn't mention is that this will also occur out of
the FM band.  It will bother Channel 6 stations below and aircraft
navigation above.  Sine the above is AM detection, it may be even more
troublesome.

Worst case in the aircraft band:

(108 * 2) - 87.9 = 128.1

Goes pretty far into the meat and potatoes of that band..

Admittedly the IBOC carriers are way down from the fundamental, but a Class
B or C station will still have a lot of RF heft on the adjacents.

Some years ago one of my former clients wanted to diplex with an existing
station at an antenna farm just southwest of Providence, and closer to the
airport.  This would have added no height to the tower, but the FAA still
had to sign off on the project.  To get their approval, the client had to
stipulate that the spurious emissions within the aircraft band could not
exceed 86db down from carrier.  Typically it's 80db.  That last 6db would
not have come easily.  I think that's representative of the standard the FAA
wants when being asked to approve changes.

Craig Healy
Providence, RI