Charlie,
What I do is null the signal with the loop. Since the RFI signals all
seem to be vertically polarized, You are looking through the loop in the
direction of the nulled signal. I site a distant object through the
loop and then get a compass bearing from the object. That being said,
rather than take careful bearings, I find it more productive to walk in
the direction of the signal while alternatively looking for a peak and a
null until the signal is very strong. At that point I can always
identify the house where the RFI is emanating.
Tom W0IVJ
On 4/1/2014 5:26 PM, n0tt1@juno.com wrote:
We carefully plotted the bearings we took on a map of our area of
the city.
I've often thought about attaching, say, a boat or auto compass to
the loop support....might make the plotting easier.
Does anyone know of a "good" model of compass that would
work for that purpose?
73,
Charlie, N0TT
On Tue, 01 Apr 2014 15:24:23 -0700 "Kenneth G. Gordon"
<kgordon2006@frontier.com> writes:
OK. My son, Brendan KB7QEU and I went out after lunch and took 8 more
bearings with one of Tom Thompson's loops which I had constructed
over
the past few days.
Tom's loop tunes VERY sharply. I intend to add a bandswitch, a large
scale,
and a vernier dial to it to make it both easier to peak and easier
to take down
a data point.
We carefully plotted the bearings we took on a map of our area of
the city.
I connected the loop to the FT-890 in AM mode (BW 6 KHz), tuned to
3573.5
KHz where "my" noise peaks, and used the FT-890's "S" meter to take
readings.
First of all, the nulls are not quite as sharp, nor as deep, as
those I get with a
shielded loop, but they suffice. (The shielded loop I was using
would
commonly show a difference from null to peak of over 30 db, while
the
unshielded loop most often provides a difference of only about 10
db).
The results we plotted are somewhat confusing to me as three of the
bearings did not result in anything common to the other five.
4 of the bearings definitely converge on an area that appears to be
around
an area of about 1 square block which is 4 blocks east of us.
A 5th is close, but outside the convergence zone of the other 4.
Signal strengths became greater as we got up on a hill to the east
of my
station which is also nearer to that 1 block area than some other
bearings.
Those three bearings that gave confusing results were the weakest
ones,
and the differences between the null and a peak were only about 1
"S" unit.
However, one odd thing is that two of those three bearings, if I
take a 90
degree normal bearing to those, both show up in the same area as the
4
"good" bearings. One, in fact, is exactly coincident at its end with
two of the
other "good" bearings.
I don't know how to read those odd ones, but I am not in the habit of
throwing out data points just because they don't "fit" either. So I
don't know
what to do about them right now.
I suppose I should drive over to that spot 4 blocks east of us and
take a look
around, then take some more bearings.
Probably tomorrow...
Ken W7EKB.
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