AM radio propagation #antennas

Rich - KN6JLF

Requesting perspectives on propagation.

Foresthill Fire District has an emergency radio operating on 1020 AM under TIS
rules.  The usual distance/signal falloff has been noted in contour mapping.
Note, no spectrum analyzer on hand, just receivers with relative
dBu/v readings.  Power is 4 Watts CW, but with 90% mod when messages are played;
PEP 7-8 watts estimated (simple power meter) Inital setup of the transmitter field density
is 2mv/.93 miles. Antenna is at 3200 MSL, in downtown Foresthill.

However, it was noted that the signal was higher, and obtained receiver quieting
while crossing the Foresthill Bridge at about 15 miles distance.  From that point towards
Foresthill, the usual PGE, growlights and cable system noises interfere as expected while running at
this low power level.  Why does it sound so good there?   Is it the bridge structure and groundwave?

Take a crack at this one Extra Class!


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