[RFI] Looking for ideas about yet another noise source

Tue Jul 14 14:02:39 PDT 2009

Which one??  old rdf stuff used a loop or ferrite antenna to find a null in
strength, Doppler df uses electronically rotated vertical array to generate
a synthetic doppler shift and determine direction by measuring the phase of
the shift.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net

> -----Original Message-----
> From: Roger (K8RI) [mailto:k8ri at rogerhalstead.com]
> Sent: Tuesday, July 14, 2009 01:35
> To: K1TTT
> Cc: rfi at contesting.com
> Subject: Re: [RFI] Looking for ideas about yet another noise source
> 
> I've never seen the circuitry, but how did the old ADF equipment work?
> Might it be adaptable with a computer and display to display and overlay
> on a GPS moving map?
> 
> 73
> 
> 
> Roger (K8RI)
> 
> K1TTT wrote:
> > Those Doppler shift antennas won't work on noise.  They require a
> carrier,
> > preferably unmodulated, to detect the Doppler shift on while they rotate
> the
> > array.
> >
> >
> > David Robbins K1TTT
> > e-mail: mailto:k1ttt at arrl.net
> > web: http://www.k1ttt.net
> > AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> >
> >
> >
> >> -----Original Message-----
> >> From: Roger (K8RI) [mailto:k8ri at rogerhalstead.com]
> >> Sent: Monday, July 13, 2009 00:47
> >> To: kb4t at arrl.net
> >> Cc: rfi at contesting.com
> >> Subject: Re: [RFI] Looking for ideas about yet another noise source
> >>
> >>
> >>
> >> Frank Haas KB4T wrote:
> >>
> >>> Chris:
> >>>
> >>> The random nature of your pulsing interference means you will have to
> >>> invest more time to find the source. It's not going to be easy and
> >>> will likely be very time consuming because of its intermittent nature.
> >>> You have the right tools so now you have to use them to the best
> >>> advantage.
> >>>
> >>>
> >> How about building up one of those "doppler shift" antennas?  I've seen
> >> them used on 2-meters and for close in work I'd think it could be
> >> adapted to 20.
> >>
> >> For years I've chased what at times can be an obnoxious and loud hash.
> >> It should be easy to catch as it's often on for some time, but
> >> unfortunately when I get the chance to chase it, every time I get about
> >> a city block to the SE it disappears and does not come back.  It's like
> >> they are watching for me...Nothing like a little paranoia.
> >> When it's on it's loud at well over S-9 including the entire 6-meter
> >> band, down to some where a bit above 40 meters.  It's normally a day
> >> time signal that is strong from the NE to S where it fades rapidly.
> The
> >> only electric fence in that direction is probably a bit over a mile.
> >> While there is one to the S that I've never heard.  There is one of the
> >> big high tensions lines that at its closest is about a quarter mile to
> >> the NE but I've never heard anything in that direction.
> >>
> >> OTOH I haven't heard it in over a year.
> >>
> >> 73
> >>
> >> Roger (K8RI)
> >>
> >>> Keep a log and note the day(s) and time(s) that the interference
> >>> occurs. Is there a time/day when it seems to occur more frequent. If
> >>> you keep a log for several days, do you note an increase or decrease
> >>> in activity.
> >>>
> >>> Is the activity level affected by environment? Day or night, warm or
> >>> cool? Prime time vs. Daytime? Trend analysis may show you better times
> >>> to hunt the source.
> >>>
> >>> If you are convinced that the source is not in your home, you will
> >>> have to start walking around the neighborhood particularly at times
> >>> your trend analysis says you are likely to hear the source.
> >>>
> >>> If the signal level varies from moment to moment you will have to note
> >>> the highest and lowest levels and try to find an attenuator setting
> >>> that gives you something in the middle. Another approach might be to
> >>> set the attenuator so the level is more or less consistently low and
> >>> start moving around to see if there are any locations where the signal
> >>> strength seems higher?
> >>>
> >>> I could go on and on but hopefully by now you see my point. Thorny
> >>> problems like yours require collecting more data and thinking more
> >>> about how you can use your tools to your advantage. Invest the time
> >>> and use your tools wisely and you will locate your source.
> >>>
> >>> I can't encourage you enough NOT to SPECULATE as to what the source
> >>> might be. In my experience, guessing what the source might be has been
> >>> a waste of time. Even with all the experience I have now, I rely on my
> >>> tools to lead me directly to the source. The only meandering I'll do
> >>> is in the early stages of the hunt when I'm trying to find the general
> >>> direction I must take to the source. Once I get a "lock" I focus on
> >>> that direction. Sometimes it takes a bit of effort to get the "lock"
> >>> but that's what the trend analysis and wide open receivers do for me.
> >>> I prefer to work smart rather than work hard. I hate to waste time so
> >>> I limit guessing as much as possible.
> >>>
> >>> Good luck & 73,
> >>>
> >>> Frank N. Haas KB4T
> >>>
> >>> -----Original Message-----
> >>> Message: 4
> >>> Date: Sun, 12 Jul 2009 02:33:05 -0500 (CDT)
> >>> From: "Christopher E. Brown" <cbrown at woods.net>
> >>> Subject: Re: [RFI] Looking for ideas about yet another noise source
> >>> To: kb4t at arrl.net
> >>> Cc: rfi at contesting.com
> >>> Message-ID: <Pine.LNX.4.64.0907120217560.19313 at tree.woods.net>
> >>> Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
> >>>
> >>> 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.
> >>>
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> >>>
> >>>
> >>>
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