[SBE] FCC R & R 73.318: FM Blanketing Interference

[A9xw at cs.com]

We made suck outs from twin lean and coax stubs. The win lead was taped to 
the owners twinlead to couple and kill the QRM,  the coax stub was used with 
a T connector just as we would a 2nd harmonic filter on a TX.  

Had one case in Topeka, KS where an apartment complex was trying to get 
stations from Kansas City, and any local TX would overload the wideband amp. In 
another building the twinlead on the amp had an open leg and was feeding 
back and self oscillating when a ham 2 miles away used his 2 meter HT that 
added just enough RF to trigger it. 

Rectification issues from home gutters, wire fences, and a telephone wire 
from AT&T laid on the ground and used iron wire. 

At WJJD we had 50 kW and a directional pattern equivalent of 75 kW toward 
Chicago. A domed church on the adjacent property had over 100 volts of RF on 
the metal dome and nearly 200 on long speaker/mic wires. Had to actually 
lower power so they could repair the gold leaf on the dome.  Internal to the 
station was a Dynaco 70, the speaker leads picked up enough RF that ut outs 
its won quite powerful signal on top of two other Chicago stations. We're 
talking 10's of miles of spurious you could hear  on a car radio on the other 
stations frequency. Fixed that with a clip lead fro the amp chassis to the 
Amplifuzzy cabinet. Had a note, DO NOT REMOVE on the clip lead. It also had 
enough residual FM that Motorola called one day to ask when we had gone AM 
stereo. 

Had another instance where QRM occurred only around 8 PM to 11 PM. Turned 
out a house near the TX site was the source. When the owner used his light 
dimmers at night, they also rectified the RF and reradiated it on the house 
electrical wiring. 

At the Prudential building the old WGN TV mast held two FM's, and we had to 
put filters on them to prevent a mix product from clobbering an Evanston 
FM, and one day two bays of the antenna blew off and landed on the park and 
roof below. But that's another story. 

Henry


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