A couple of comments:
I just bought ($25) a Marine DF, with BFO, 3 bands 0.15 to 5MHz, & VHF
FM, has D battery as well as 12v. Optical sights, S meter, sense
antenna as well! Pretty good RFI DF I think. Aqua-Guide CH-704 Marine
Direction Finder. If anybody has documentation, a copy would be greatly
appreciated.
A nearby pole had its ground wire cut and the remaining length was a
perfect length as a 40m vertical. PSE was quick to fix it when logged
as a safety problem. However, the "ground" for a pole might be a single
rod or a spiral wrap of the wire when the pole was dropped into the
hole, so ground wires are likely decent radiators.
I also have a Lokata 7 LF/BCB DF handheld from my way back sailing days,
a top rated handheld DF, digital freq readout but it is dead, so also
looking for schematics for it.
Grant KZ1W
Redmond, WA
On 1/13/2020 03:51, AA5CT via RFI wrote:
Scott,
The marine DF receiver (with the "sense" antenna to give a
cardioid pattern) in use by myself (and a few others) covers
the old "marine" band as shown on the scale as 1.6 MHz
through 4.0 MHz and _not_ the (now) traditional VHF band
(using FM) near 156.8 MHz ("CH 16").
Also it's rx mode is AM. Sorry for the confusion.
I have used it with the ferrite loopstick vertically oriented
(for horz polarization) and reception goes to nil in that case,
so it works out just fine leaving it oriented for incoming
vertical plane waves.
When "inspecting" a noisy pole with the UHF beam I do note
a difference when rotating the beam; this is trivial to perform
but does show that various 'elements in the structure' (wires)
are preferential to the radiation of the RFI 'noise' over others
at the much shorter UHF (450 MHz) wavelengths (a factor of
over 100 'shorter' over the wavelengths of the old "marine"
band.)
The hypothesis (my hypothesis) to the radiation of power
line noise (___for the HF low bands____) is the ground wire
running along the pole does the majority of the "radiating".
Just imagine a T-top vertical antenna; that antenna is a
vertical radiator and the opposite 'currents' in the T-top
wire generate magnetic fields opposite in direction. The
T-top wire is the active phase line(s) involved in the creation
of the noise, and it could also include the neutral wire.
If you've ever seen the demonstration video by N4IS (Jose
Carlos) of the large Waller Flag (works on 160m and 80m)
you will note when he rotates the flag horizontal ALL the
(what sounds like) power line noise __goes away__, leading
one to conclude that the majority (if not all) of the local
low band HF/MW (160m and 80m) 'noise' is vertical in nature.
de AA5CT
.
. On Sunday, January 12, 2020, 11:12:47 PM CST, K9MA <k9ma@sdellington.us>
wrote:
With any kind of direction finding antenna, you have to be aware of
polarization. A vertically polarized loop, for example, may give very
misleading bearings if the noise happens to be mostly horizontally
polarized. When I walk around with my 135 MHz yagi tracker, I rotate its
polarization as I sweep around in azimuth, and often find the most
distinctive peak with it mostly vertically polarized.
73,
Scott K9MA
On 1/12/2020 15:18, AA5CT via RFI wrote:
This may be a case where the marine DF receiver succeeds, and a
simple DF loop fails.
With the simple DF loop one is unable, repeat, *unable* to resolve
the __180 degree ambiguity__ that the 'null' of a simple loop gives.
The BIG, and this is NO slight advantage offered by the marine DF
receiver is the utilization of a "sense" antenna that works in combination
with the built-in loop antenna to 'synthesize' a cardioid or unidirectional
antenna pattern.
WITH THIS feature one can actually 'sweep' around the compass rose
and get a feel for where the strongest noise is coming from, like pointing
a Yagi antenna around, but on 160 or 80 meters! On the other hand, the
simple loop can ONLY give a one a NULL, and there remains the choice
of which direction, which bearing the 'source' lines in, because of that
180 degree ambiguity.
Also with the simple loop one cannot 'scan around' for the strongest
signal, whether that signal is a 'broad band' white noise (LIKE I get
from a car wash in my area) OR impulse 'buzz' noise from power
line arcing sources.
IT REALLY IS pretty cool to 'twirl' the direction knob on one of these
Coastal Navigator Marine DF receivers and HEAR the different 'arc'
signatures or sounds coming from different directions.
Maybe this is where we're getting hung up up? All my DFing for
any noise nowadays makes use of the marine DF receiver with the
sense antenna and that directional Cardioid pattern.
If IT emits, its a simple matter of taking two bearings sufficiently
spatially spaced apart and "x" marks the spot of the source. I now
use Google maps and 'null' bearings taken from my DF receivers
to pinpoint distant sources.
One technique I've used too is to 'set out' after one of these sources on
my trail bicycle, and through the use of null DFing and the Sense/Cardioid
function eventually locate OR determine the source is further way than
first thought. If I get down the road a mile or so AND the DF receiver is
still indicating the SAME direction, I'm looking at a source that is now
on the order of 4 to maybe 5 miles way, and as I've written, I've had a
couple just like that!
de AA5CT
.
.
On Saturday, January 11, 2020, 9:03:04 PM CST, Kenny Silverman
<kenny.k2kw@gmail.com> wrote:
KC4D,N3AC and N3CW went hunting with a KX3 and a DX Engineering Amplified RX loop and again didn’t find anything conclusive. Basically they said the loop performed about the same as one of the AM radios we have that’s fairly directional.
We’ve been looking so many times that we’re getting frustrated. There are a few noisy
clusters, but we can’t find a specific pole or house. Nor can we assess if the noisy areas are
actually the key offender(s)
Do we call in the clusters we found ? Or do we really need to pinpoint the source(s)
better before we ask for crews to come out? We’re concerned about crying wolf
and/or giving a list of more than a dozen poles for the power company to look at.
Regards , Kenny K2KW
P.S. the only success so far is fixing my subject line typo 🤓
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