[TowerTalk] AM Broadcast Harmonic Interference to 75 Meters

k1ttt.dave at gmail.com k1ttt.dave at gmail.com
Sat Dec 5 12:15:44 EST 2020

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 at arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: telnet://k1ttt.net:7373

-----Original Message-----
From: TowerTalk <towertalk-bounces at contesting.com> On Behalf Of Byron Tatum
Sent: Saturday, December 5, 2020 11:15
To: Towertalk Reflector <towertalk at 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 that 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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