Red Wave Radio

What does an AM transmission sound like when heard on an FM receiver?
How about an IMAGE of an AM transmission heard on an FM band?

Occasionally, (on average, once an hour) I hear what sounds like off-
frequency splatter from an adjacent channel close to the one I
have tuned in my scanner.  The frequency I'm tuned to is 154.935,
which is Ohio L.E.E.R.N. (used for police mutual aid, etc.).

The transmission I hear is audible but garbled, but definitely not
the "Donald Duck" sideband, but more like bleedover (splatter)
you hear on an adjacent CB channel if someone is transmitting
really close by.

I can't make out what the person is saying, but I do seem to hear
that familiar (400Hz?) background hum you hear on most tranmissions from
aircraft on the AM Air band.

My first assumption is that its simply off-frequency bleed, so I set
the scanner to scan three frequencies above and three below the
154.935, in the usual 5Khz spacing (.920, .925, .930, *.935*,
940, .945, .950) in hopes of "bracketing" the bleedover and catching
it on a frequency nearby.  No luck. This lead me to think that perhaps
I was picking up an AM Air frequency image in the 150MHz FM VHF band.

So, I whip out the calculator and sure enough,
154.935 - 21.4 (2*10.7 IF) = 133.535 lands me right in the
AM Air band.  Three questions:

1. What does an AM transmission sound like on FM? Garbled?

2. What is the likelihood that an AM image will show up and
break squelch on an FM band 21.4MHz above?

3. 133.535 MHz I do not recognize as any frequency being used
by either Cleveland Hopkins or Akron/Canton airports. Does not
show up anywhere in Police Call. (which really did not surprise me)
Any insight from anyone?

Stumped,

Mike

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Michael Mayer, Senior Technical Support Engineer      Amateur Radio KB8RJO
Visual Numerics, Inc.  32915 Aurora Rd.  Suite 160, Solon OH  44139  USA

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|>3. 133.535 MHz I do not recognize as any frequency being used
|>by either Cleveland Hopkins or Akron/Canton airports. Does not
|>show up anywhere in Police Call. (which really did not surprise me)
|>Any insight from anyone?

Most airband transmissions are on 50KHz spacings, especially the
low altitude frequencies. This is for compatability with the older
360 channel radios still used in some older GA airplanes. Where
congestion is a problem, frequencies with 25KHz spacing are being
utilized. Since aircraft which fly in Class A airspace (above 18,000
feet) are required to have 720 or 760 channel radios, many of the
25KHz frequency assignments are used for high altitude sectors.

My spectrum allocation info lists the 132.025 - 136.075 band as
being allocated to ATC voice use (as opposed to ground control, FSS,
or Arinc, but isn't more specific. Most of the listings in this
band for the east coast are for ARTCC air-to-ground communications.
You might want to check in the latest Airport/Facility Directory
in the section marked Air Route Traffic Control Centers.

Intel Corp.
American Fork, UT

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