"norml" wrote
KGO's system favors the north-south directions and disfavors east-west
transmission.
Your gold country home is in a "null" direction from the KGO transmitter
(at the eastern end of the Dumbarton bridge).
In such areas, the phase interference produced by the transmitting antenna
causes distortion in receivers.
_________________

Distortion of this nature usually occurs only very close to the transmit
site (a mile or so). Note that if KGO was transmitting distortion toward
ldbk's gold country site, she also would hear it there on her stock car
radio. But she says her car radio "tunes in KGO perfectly."

While KGO radiates less power toward the gold country than KNBR, the signal
strengths of each are defined more by groundwave losses than by their
radiated power. For example, the 2.5 mV/m groundwave field strength contour
for KNBR passes about 60 miles beyond Sacramento, while for KGO it is about
20 miles beyond Sacramento -- and this includes the differences in their
radiation patterns.

Probably the reception that ldbk notes is based more on the sensitivities of
the radios, and the locations where they are used. Radios used inside a
building have less signal to work with because the wiring in the building
can act as a shield. Aluminum siding just about kills AM reception except
in very strong signal areas. Also there could be a lot of interference in
the building (light dimmers, touch lamps etc).

Rotating/moving the CC radio around the building may help reduce noise by
capturing more signal and/or rejecting some of the local noise sources.

RF (retired broadcast engineer)