[BC] Closest-frequency AM diplexes

[tosenkowsky@prodigy.net]

>( if I measure 87db at the tx output, why is it 54db in the field ? )

External influences. I used to perform NRSC measurements for an AM DA
in CT. If I measured in a McDonald's parking lot I measured third
harmonic about 30 db down. Went 1/4 mile beyond, measured 85 db down.

Classic example from years ago. A local ham complained to the FCC
that an AM station had harmonics in the ham band. The station CE
said he did a proof and harmonics were barely audible on a shortwave
receiver at the station. FCC inspector arrives at the ham's residence
near the station and measures harmonics about 20 db down. Inspector
goes to the station, tells the CE and GM there are harmonic issues.
CE says "Show me". Inspector goes to the van, no harmonics. Goes back
to the house. Harmonics. Culprit: Neighbor's downspout/gutter had a
poor connection. Diode effect. Instant harmonics.

I would look for loose connections, poor bonding, etc. Track it down
with an FIM. I had a Kahn AM Stereo install. A lot of noise in
stereo, not in mono. Not showing up on scope, mod monitor etc. but
was very audible in stereo within 1/4 mile of the station. I cured it
by placing a wire over the vibration dampener on the A/C duct system.
Vibrating ductwork caused L-R phase noise!

Tom Osenkowsky, CPBE

--------------------------------------------------------------------
mail2web - Check your email from the web at
http://mail2web.com/ .