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

To: rfi@contesting.com
Subject: Re: [RFI] Mystery 70 cm Repeater Input RFI/EMI?
From: digital-conjurers@roadrunner.com
Date: Thu, 11 Oct 2007 17:03:48 -0700
List-post: <mailto:rfi@contesting.com>
Yes, the machine does have PL...and the tone is the reset courtesy tone.

...and I don't think it's just our machine, as two of the other 440 
machines affected are owned by other clubs/individuals, on different 440 
machines; but they're all on the same mountain site.  The hunch is that 
something on that mountain is giving everyone grief, though no-one can 
pinpoint it.


At 02:13 PM 10/11/2007, you wrote:
>Lin, although it's just a shot in the dark, we had similar popping sound 
>on a DB224 that had 2 of the 4 dipoles cracked all the way through the 
>center of the 2 dipoles. Maybe lightning, maybe it got water in it somehow 
>and split when it froze.  With 2 good dipoles, the DB 224 will still show 
>a low SWR. But that noise at the first of the one mp3 that is just keyed 
>down, that is a weird little tone at the start, but I didn't hear it come 
>back on again. Is that weird little tone frequent also, or just the 
>popping and cracking? The repeater does have PL so that isn't a constant 
>irritation doesn't it?
>----- Original Message ----- From: <digital-conjurers@roadrunner.com>
>To: <rfi@contesting.com>
>Sent: Thursday, October 11, 2007 19:46
>Subject: [RFI] Mystery 70 cm Repeater Input RFI/EMI?
>>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,
>>RFI mailing list

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