You might want to query the rfi reflector... also consider something close to
you, even a neighbor's house, that might be picking up the primary, rectifying
it, and modulating it with a 10khz switcher harmonics. Had something similar
to that here where a wall wart was generating and modulating harmonics.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: telnet://k1ttt.net:7373
-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of Byron Tatum
Sent: Saturday, December 5, 2020 11:15
To: Towertalk Reflector <towertalk@contesting.com>
Subject: [TowerTalk] AM Broadcast Harmonic Interference to 75 Meters
Hello- Can someone point me in the correct direction, in finding technical
help and someone to make measurements, regarding a problem I have at my new QTH
involving harmonic interference from a local AM broadcast station? Here are
some details - The station is licensed for 5.0 KW daytime / 1.0 KW nighttime
power levels. The transmitting site is 2.5 miles from my QTH. The transmitting
antenna is approx 240' of 65G tower on an insulated base with steel guy wires
broken up with insulators. An old FM broadcast antenna is mounted on top of the
tower but is not in use I was told. The station broadcasts on 1290 Khz. My
problem is an extremely strong harmonic at 3870 Khz both day and night, plus
there is crud every 10 Khz from about 3600 Khz to 3960 Khz. I have received
this interference in a very similar manner on my FTDX-5000MP in combination
with the Micro-Tune RF filter and on a well aligned R-390A. I don't believe it
is my equipment. I contacted the station owner and he told me tha
t he made measurements and is within the FCC limits. I do understand that the
station can be emitting a signal within FCC limits of harmonics and the
harmonics can be generated in surrounding objects such as dis-similar metals or
corroded joints. The crud every 10 Khz indicates to me some serious mixing
products being generated somewhere. I feel that I need to find a Ham who has
analyzing equipment and knowledge of this subject who can come to my place and
make measurements and guide me onlooking into this.Thanks,Byron W5FH
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