[RFI] Broadcast station RFI Mixing

[Util.RFI.pro]

I've been reading this thread with some interest as I recently had to prosecute an interference case for a ham who was experiencing peculiar interference on specific frequencies and portions of the 80 meter and 40 meter bands. 

I listened to his receiver and could tell from the sound of the interference that he was experiencing the mixing of continuous transmissions most likely AM broadcast. I surveyed the area around the customer's home listening on the same frequencies on which the customer was hearing the (now confirmed) mixes. 

Within a short time I had pinpointed 3 places where the mixes were occurring: 1) a utility pole near one of the two AM broadcast antenna sites; 2) another utility pole fairly close to the customer's home and; 3) a house next door to the customer's. 

I didn't do anything about source #1. Source #2 turned out to be a joint between the top of a "downguy" and the eyebolt to which it was attached. Repositioning the loose downguy eliminated the mix and silenced that source. Source #3 was very difficult to pinpoint and disappeared a few days later as temperature and humidity changed. I was pretty sure one of the gutters along the front of the neighbor's house was the source of this closest mix. 

All 3 sources vanished as the weather conditions changed. Temperature and humidity definitely affect the character of whatever gap is rectifying and retransmitting the mix. 

Like most other sources of interference, good direction finding skills will reveal the source. Once you know what and where the source is, finding a solution becomes easier. Ultimately, equipping oneself with the right tools to DF sources at any frequency and practicing enough to make locating sources fairly quick makes it possible to most effectively and quickly begin the resolution process. 

73, 

Frank N. Haas KB4T
Utility RFI Investigator


> On Apr 20, 2014, at 3:52 AM, Jim Brown <jim at audiosystemsgroup.com> wrote:
> 
>> On 4/20/2014 12:14 AM, Dale J. wrote:
>> I have a similar situation here, two radio stations one about a mile and is 10KW with the pattern North covering the entire Twin City area, the other station is about 8 miles is a 50 KW station.
> 
> These mixes can be ANYWHERE -- in the transmitters of the stations themselves, or in rectification in any non-linear junction. I experienced them in a very dense part of Chicago and never chased them down.
> 
> To do that, you must drive/walk around and do a location on the source, listening on the frequency(ies) where you hear the mix.
> 
> 73. Jim K9YC
> 
> 
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