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[RFI] Mystery 70 cm Repeater Input RFI/EMI?

To: rfi@contesting.com
Subject: [RFI] Mystery 70 cm Repeater Input RFI/EMI?
From: digital-conjurers@roadrunner.com
Date: Thu, 11 Oct 2007 12:46:54 -0700
List-post: <mailto:rfi@contesting.com>
Hi all,

A local 440 machine here has been plagued with a "popcorn-like" noise on 
the input with all but the strongest input signals.  It's got everyone 
baffled.  The clues so far:

1. The noise is less noticable on strong input signals, but still present. 
(Recording posted at URL below.)

2. On weak input signals, the noise is horrific. (Recording posted at URL 

3. The transmitter was turned off at the site, and the noise could _still_ 
be heard on the input. (!)

4. The repeater is atop a 5500 ft mountain, along with LOTS of other 
services, and I believe a 6 megawatt radar installation is within 20 


 From what I understand, eveything on the repeater was gone over with a 
fine-toothed comb several times over several trips/months, and no 
results.  The trustee says that tapping the "T" connector coming from the 
duplexer made some _very_ slight difference in the level of the noise, but 
he didn't think that it could be responsible for the problem.  The problem 
can disappear for days, then come back with a vengance.

I'm posting this for him, as he's swamped with work right now, and I agreed 
to take the problem up here, where all the expertise is. :)  He made one 
recording, I made another, two files:

"Repeater noise 1" is a QSO that was made with a station transmitting in 
the clear, with a beam, at good power, line of sight.

"Repeater worst case popcorn sound" is made by another station, using lower 
power,  no modulation, just keyed down to keep the input open.  Both 
stations are fixed, so that's not mobile popping you'll hear.

The theory right now is that it's some wierd RFI from some new kind of 
radar, but it doesn't seem to have a "sweep" pattern.

As Groucho said,

"Any questions?"
"Any answers?"

Files are at:


Thanks to the group in advance,


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