Joe,
It's not a multiple of the distant broadcaster.. Note what Dave said
about mixing. Here are Reno AM stations
from http://en.wikipedia.org/wiki/List_of_radio_stations_in_Nevada:
KHIT <http://en.wikipedia.org/wiki/KHIT> 1450 AM Reno Lotus Radio
Corp. Sports
KIHM <http://en.wikipedia.org/wiki/KIHM> 920 AM Reno IHR Educational
Broadcasting Religious
KJFK <http://en.wikipedia.org/wiki/KJFK> 1230 AM Reno Americom Las
Vegas Limited Partnership Talk/Personality
KKOH <http://en.wikipedia.org/wiki/KKOH> 780 AM Reno Radio License
Holding CBC, LLC News Talk Information
KPLY <http://en.wikipedia.org/wiki/KPLY> 630 AM Reno Lotus Radio
Corp. Sports
KXEQ <http://en.wikipedia.org/wiki/KXEQ> 1340 AM Reno Azteca
Broadcasting Corporation Regional Mexican
KXTO <http://en.wikipedia.org/wiki/KXTO> 1550 AM Reno First
Broadcasting of Nevada, Inc. Latin Contemporary
blanks are deleted FM stations
I'll assume your victim is near a local AM transmitter. Try an AMBC
highpass filter in front of the victim radio,
as both harmonics generated in the RF stage or mixer AND mixing products
of combinations of local high power
stations in a rigs' mixer can quite easily beat with a normally strong
though more distant station with effects you describe.
If it doesn't help, you may be seeing IM generated at the local
transmitter site (there may be collocated antennas or even a shared
antenna) mixing with the Sacramento station.
Also, see if you can make out modulation that correspons with signals
you hear from your local stations.
I don't have an IM calculator on the computer, and one I found doesn't
seem to like my display, but poke around
on the net and you may find one.
Oh, and cut power to any cable or other broadband. In fact... turn off
ANYTHING that might be generating a carrier locally. Especially if it's
on a timer. You might be surprised what dwells in, well, dwellings.
Good luck,
Cortland
KA5S
On 9/18/2012 1315, Joe wrote:
----- Original Message -----
From: "David Robbins" <k1ttt@verizon.net>
Subject: Re: [RFI] AM Radio Interference On 75 meters
3960khz is not a harmonic of 1530khz so something else is also happening here.
listen carefully to the kfbk signal and see if there is some other signal
mixing with it. check for other harmonics and other signals that it might be
mixing with to end up on 3960...
1530 + 2430khz?
1530*2 + 900khz?
1530*3 - 630khz?
1530 + 2*1215khz?
5490 - 1530khz?
etc, etc.
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