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Re: [RFI] Looking for ideas about yet another noise source

To: kb4t@arrl.net
Subject: Re: [RFI] Looking for ideas about yet another noise source
From: "Christopher E. Brown" <cbrown@woods.net>
Date: Sun, 12 Jul 2009 02:33:05 -0500 (CDT)
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>

I have a Grundig SW rig, but I find the HT (wideband receive w/ AM) with a 
step attenuator and a small shielded loop to be more useful.  Also have a 
simple coax faraday pickup for in close.

The issue is that the signal is strong but *SHORT*, think snap your 
fingers short, and while it may repeat after a few seconds the long term 
average is a couple times a minute or less.

If I had a second or 2 to rotate the loop...  But I don't.

I even tried connecting the loop to the main tranceiver mounted to the 
desk so that I could try to plot long term averages while rotating the 
loop 5 deg every 10 minutes.  Only problem, the peak reading for the pulse 
varies up to 40db from pulse to pulse.

I am pretty much down to guessing likely canadates, adding enough 
attenuation to lose the pulses, and then placing the loop phyically close 
to suspect devices and waiting.  The only thing I do know is that it is 
not in home or a reciever generated issue.  All AC power cut, still there. 
2 seperate HF rigs and an HT on three seperate antennas, still there on 
all three.

Even went as far as listening on one receiver/antenna, then cutting power 
to that receiver and powering up another just to totally rule out the 
radio gear as a source.

I keep hoping that whatever the device is it is some form of 
"statekeeping" status, and that I can catch it in an active state 
generating pulse trains of 10 seconds or longer so I can properly DF it.

On Sun, 12 Jul 2009, Frank Haas KB4T wrote:

> I would use a handheld shortwave receiver (Grundig E5 or equivalent)
> and take a walk around the house and neighborhood when the
> interference is occurring with some regularity. The receiver would be
> tuned to the frequency at which the signal is strongest until I got
> close then I would either tune off the strongest frequency slightly
> and look further for an increase in signal strength or tune to a
> harmonic multiple of the strongest frequency to see if the strength is
> lower.
> The receiver should have some sort of signal strength indicator and an
> attenuator. The high end alternative would be something like the ICOM
> R-3 with a step attenuator attached via a barrel male BNC adapter and
> a small loop antenna to find nulls.
> I have tracked down HF interference sources using a small loop antenna
> I bought from Antennas & More (If I recall correctly) and an R3. By
> walking or driving in a circle (more or less) around the perimeter of
> the interference, I was able to find nulls and draw lines on a map.
> Where the lines crossed I went in close and found the source.
> Sometimes, if you are lucky, pulsing sources will be rich in harmonics
> so that when you get in close you can hear them at successively higher
> frequencies into the VHF spectrum. If I can hear the source in the VHF
> spectrum I can usually DF it with a smallish Yagi and a receiver with
> an attenuator.
> Good luck!
> 73,
> Frank N. Haas KB4T
> -----Original Message-----
> Message: 1
> Date: Sat, 11 Jul 2009 02:44:11 -0500 (CDT)
> From: "Christopher E. Brown" <cbrown@woods.net>
> Subject: [RFI] Looking for ideas about yet another noise source
> Attempting to track down a bothersome very intermittant noise and
> looking for some ideas.  Don't have a decent way to record it, but may
> need to set something up if I cannot make headway.
> Noise is pulse, appears on at least 80-20, strength higher around 20.
> On the lower freqs, it is more of a static rush but time compressed,
> it is also seemingly random, twice in 5 seconds, nothing for 40 sec,
> once, and so on.  Seems to be there almost any time of the day or
> night.
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