-In your case, I assume that you are flying either far enough horizontally
-away from or high enough above the antennas for safety. Let's say a minimum
-of 1/2 mile horizontally. Now lets assume that the strongest broadcast
-signal is 100,000 watts "effective radiated power" and a frequency somewhere
-around 100 MHz.

In a metropolitan area 100kW ERP would rank you in the lower third of broadcast
signals, but for grins and giggles, let's make that presumption.



At a distance of 1/2 statute mile the power from that
-signal that would be picked up by an aircraft com antenna would be about 10
-milliwatts.

More like 5 milliwatts, but let's not debate how many milliwatts can dance on
the head of a dipole.


This is a spectacularly strong signal for purposes of
-reception, and certainly more than enough to make it impossible for the
-attached receiver to pick up any other signal, but nowhere near strong
-enough to cause the receiver, if not otherwise powered, to generate and
-re-radiate an intermodulation product.

Oopsie. 10 milliwatts is about 0.7 volts RMS, or about a volt peak. If for
whatever reason that front end were wide open to the interfering signal, a volt
is sure as little green apples capable of turning on the B-E diode of the RF
amplifier. Now any lower power signal is perfectly capable of being mixed with
our newfound "LO" and being reradiated.


-
-So, if the signal WERE strong enough to provide enough power to cause an
-otherwise unpowered receiver to generate and re-radiate an interfering
-signal, the same powerful signal would pretty much wipe out operation of any
-other nearby receiver that IS powered on.

Ah, no. NOt if the other receiver had enough filtering in the front end to get
rid of it.

-
-By all accounts, what you have is plain old garden variety intermodulation
-interference. The intermodulation products doing the interfering are being
-generated in the same receiver that is being interfered with. In an earlier
-post I offered a relatively simple way to prove this.

I'm not debating that it is intermod. I don't know. I'm not there. But front
end reradiation is a phenomenon that should be investigated also. And, for that
matter, that is exactly why two brands of ELT have had factory recalls...the C-B
junction in the output transistor was a wonderful intermod generator.

Jim

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com