RF interference issue again (esp. for E Drucker and Jim Weir and other RF wizards)

I respectfully disagree with this statement. There is precious little that is
engineered as well as a commercial radio station. Even sloppy maintenance
wouldn't get the sidebands this out of whack...and besides, those sidebands
would have to be from the FM band, and we are talking about 20% away from the
carrier. Ain't no way.

I live next door (literally) to a 10kW AM transmitter, and occasionally I tune
the spectrum analyzer to their frequency and put an 80 dB notch filter on the
center of the carrier. With a 120 dBm noise floor, I **still** can't see any
splatter outside their allocated bandwidth.

While aircraft radios are generally good with filters, also, there comes a limit
to any design when the volts coming in the front end are just too much for the
microvolt amplifiers. It is called fundamental front end overload, and we are
all susceptible to it.

Both Microair and King use varactor tuned filters in the front end for
selectivity. While these are good design choices, you must remember that a
varactor is nothing more than a diode, and a varactor is one of the best
multipliers in the world. Whap that front end diode with a couple of volts and
you've got a little comb generator second to none.

I think we'd best look elsewhere for the solution.


Jim




"Bill Daniels"
shared these priceless pearls of wisdom:

-I think the commercial stations are poorly controlling their sideband
-radiation and some of their RF power is spilling onto the aviation band.
-Aircraft radios are generally well designed and reject signals that are not
-intended for them, but they can't do anything about spurious signals from
-sloppy maintenance at a commercial radio stations.

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

"Jim Weir" wrote in message
...

I think we'd best look elsewhere for the solution.

Sounds like intermodulation to me. Look for a sum/difference with the
frequencies at the antenna farm?

Rich S.

In article , Rich S.
wrote:

Sounds like intermodulation to me. Look for a sum/difference with the
frequencies at the antenna farm?

That's my thought. I used to fly over Voice of America's transmitter
farm in southwest Ohio before they shut it down. Their transmissions
always leaked into the aircraft radios when in close proximity.

"Rich S." writes:

I think we'd best look elsewhere for the solution.

Sounds like intermodulation to me. Look for a sum/difference with the
frequencies at the antenna farm?

I'd ask other owners. Then try to find your regional FAA frequency
coordinator or similar, in other to locate a sympathetic ear. He'd
know who would go by with a 494 spectrum analyzer or such...iffen they
ever have time.

It could well be intermod from tower guy joints or such. It could
also be the front end of the radios. (Don't suppose you have 3 element
cavity tha would fit in the back seat ;-?)

If all else fails, maybe filing a NASA report would get a response.
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433