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Re: [RFI] Excellent RFI notes by ON4WW

To: rfi@contesting.com
Subject: Re: [RFI] Excellent RFI notes by ON4WW
From: Jimk8mr@aol.com
Date: Mon, 27 Dec 2010 19:14:34 EST
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
In the spirit of passing on stories of odd sources of RFI, here is one that 
 was recently solved at K8AZ:
For several years we had intermittent problems of interstation  
interference at Tom's Multiop contest station, with the 20 meter station 
interference on 15 meters. it wasn't always there, but was mostly observed  
transmitting on the 20 meter stacks about 100 feet from the house. Not a  
problem when using the multiplier station stacks on a rotating tower about 
300  feet away.
During the CQWW SSB this year we noticed that this noise was appearing in a 
 20-30 KHz spread of garbage at 1.5 times the 20 meter frequency, i.e.  
transmitting at 14220 would center the garbage around 21330. 
After the contest I spent an afternoon on the tower checking connectors,  
bypassing relay boxes for the 20 meter stack, even trying an alternate 
feedline  normally used on the 15 meter system.  No success.
So we next took an IC-R10 scanner, using the rubber duck supplied with that 
 radio, through an ICE 15 meter filter to avoid any fundamental overload  
problems. Lots of sniffing around, while reducing the transmit power to the  
minimum amount that would cause the interference (about 40 watts with the TX 
 stack pointed at the east end of the house would do it). We found a hot 
spot  near the garage door opener, but totally disconnecting the opener did 
not  eliminate the problem.
I had pretty much run out of time that day, so I left, with Tom's next step 
 to unhook a number of wall warts run from a power strip in his bedroom, 
located  pretty much right over the garage.
With the strip unplugged the QRM disappeared. He then started plugging them 
 back in one at a time.
The culprit?
The one that powered an XM Satellite receiver. The receiver was originally  
intended for automotive use, with a low power FM transmitter to couple the 
XM to  the car radio.  The transmitter section was being grossly overloaded 
with  HF RF from 20 meters, causing it to put out RF garbage at who knows 
With that radio out of service, the 20 and 15 meter ops at K8AZ were able  
to very peacefully coexist in the CQWW CW test.
73  & HNY to all   -   Jim    K8MR
In a message dated 12/27/2010 12:58:44 P.M. Eastern Standard Time,  
jim@audiosystemsgroup.com writes:

On  12/23/2010 4:03 PM, Tim Duffy K3LR wrote:

> http://www.on4ww.be/emi-rfi.html

Yes, this is truly  excellent work.  Required reading for anyone active 
on the ham  bands.

73, Jim K9YC
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