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Re: [RFI] RFI Direction Finding

To: "'Jim P'" <jvpoll@dallas.net>, <rfi@contesting.com>
Subject: Re: [RFI] RFI Direction Finding
From: "Ed -K0iL" <eedwards@tconl.com>
Date: Sat, 18 Feb 2006 12:29:15 -0600
List-post: <mailto:rfi@contesting.com>

This has drifted far off from where the original question was, which was how
to make/use a loop on 40 mtrs to track noise.  I was simply giving some
"general" guidelines from my experience and those of other professional
power company RI guys.  You seem determined to dive off into specifics for
which we haven't been given any information yet.  

Of course there are exceptions to the "rules", which are actually
guidelines, not rules.  But we don't have any info from the guy on the
specifics since he's just getting started.

Most of what you say is true: never start a search on UHF for a noise you
hear on HF that could be far away; some FM radios do pick up impulse noise
(which I stated), but usually at a lower sensitivity that a good AM rcvr
would, and you have to take into account the limitations of your equipment.
I think you'll find I said the same things overall if you stop looking to
tear apart each individual paragraph.

Now back to the first question of tracking on 7 Mhz with a loop; some good
things to look at before starting a PL noise search can be found in the
"Interference Handbook" by William Nelson & Bill Orr.  Even though the
book's a bit dated, powerline technology has not change too much over that
time.  Fig 1 (pg 54) and Fig 5 (pg 58) shows the range of noise given
different freqs/bands.  Another is Fig 1 (pg 104) showing standing wave
effects from a transimssion line.  What's interesting here is a peak in the
horizontal is a null in the vertical and vice versa.  Anyone tracking a
source needs to keep these things in mind simultaneously when tracking a

One limiting factor will always be the amount and type of equipment
available to the investigator whether he's a ham or a power company
employee.  If a ham is trying to find the source to speed up response time
and repairs, it's important that he get it right before calling the power
company or he'll get a reputation that might hurt his response the next

There was also an excellent article in QST last year or before that
discussed a fast method of getting a kind of "fingerprint" of the offending
noise on a storage scope, then searching for that specifc noise in the
field.  I have the book by the same author at work (Marv Loftness).  There
are also some good tips on Mike Martin's site at http://www.rfiservices.com/
who teaches seminars on Loftness' tracking technique and does consulting
work for power compaies.

Just some things to think about before heading out with the HF loop.  Good

73, de ed -K0iL

-----Original Message-----
From: Jim P 

> The FM broadcast wouldn't be affect on an FM radio since noise is
> "Amplitude" in nature.  FM rcvrs won't pick them up (usually, although
> rcvrs may).


Not these cheap ratio-detector equipped FM radios with only
4 transistor IF stages - which I used to check this phenom (these
radios aren't equipped with a full set of 'limiter' stages followed by
the usual Foster-Seely discriminator).

> Most powerline noise sources, when you are in the neighborhood, do emit
> VHF high-band real nice and sometimes even lower UHF portion locally if

Only a partial "Bzzzzzzt! on this one.

An attempt on this basis to establish correlation of a particular source
and it's 'effect' that one has in his shack may fail given a rock-hard
assumption in this area.

Take for example, again, where the ham who took his Two Meter
Beam could not locate this source using VHF alone.

> have a sensitive enough rcvr at those freqs.  I am not referring to ham
> bands here, just generic VHF (30-300Mhz) & UHF (300-3000).  At work we use
> somewhere around 250-300Mhz and usually have to start turning the gain

I pointed out a specific case where a general assumption did not
work; I just want to point out to people that there are no hard, fast
rules to this game, there are exceptions..

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