Hi Dave,
I still recommend tuned and untuned loops to folks on an almost daily basis
but they definitely don’t shed as much light on the situation as a
unidirectional antenna does. It would be nice to see what your shielded
untuned loop design is.
The beauty of the portable flag which is unidirectional is that you
typically can walk right to the source (no guessing which direction the
signal is coming from). I still pack 7 antennas when I go on a RFI case,
and this includes 3 tuned HF loops, but I have found that I typically don’t
use bidirectional loops anymore (unless I’m trying to be more stealth) as
the portable flag saves me an enormous amount of time. Also in heavily
congested areas (like downtown Indianapolis) having the unidirectional HF
antenna is priceless as it unmasks noise that’s mixing from other sources
that are in the opposite direction, etc. Yesterday I worked on a case
(more of a country setting) where I had 2 different bad poles that were
only 0.14 miles apart plus a 3rd RFI source generating spikes every 1 KHz
within the same area and having the unidirectional HF antenna helped me
locate all 3 sources in a matter of minutes (way under an hour).
You can never have enough antennas in your direction finding bag of tricks
but after using a unidirectional HF antenna like the portable flag for
direction finding I can’t imagine not using one. It typically takes me
seconds to tell which direction the signal is without the need of
triangulation, etc. Traditional triangulation has almost become a thing of
the past for me.
I also have been helping a ham that has the MFJ unit (the one with a beam
and the one with a dipole) and while it has helped him, it has an odd
characteristic that makes the meter jump which causes confusion to him and
after looking at the schematic I question how they implemented AGC in those
units. I’m starting to think AGC in a radio direction finding system is
typically not desirable. Manual attenuation is priceless but I don’t want
anything changing gain automatically.
Just my opinion from tracking down RFI on an almost continuous basis in
addition to my day job.
Please share details on your shielded untuned loop and thanks.
73,
Don wd8dsb
On Mon, Mar 22, 2021 at 1:22 PM David Eckhardt <davearea51a@gmail.com>
wrote:
> We recently found a faulty lightning 'arrestor' on a pole by using both the
> MFJ device and a small shielded loop (easy home brew project) into a
> battery-powered receiver. We had two of us in the field. One wielded the
> MFJ and I had the small (0.5-meter) shielded loop fed into the Yaesu VR-500
> on 1.830 MHz (160-meters). We both independently found the same source /
> pole in the field. The null on the shielded loop is extremely sharp and
> this piece of hardware should be in the bag of tricks of anyone sleuthing
> RFI. It is a powerful tool when coupled to a battery-powered receiver with
> its extremely sharp null (perpendicular to the plane of the loop). One
> doesn't need something as large as the 'Flag" that was recently published
> in QST and referred to in a previous post in this thread. Another plus
> for the shielded loop is that in the field, one can tune the receiver to
> the worst-case frequency of the RFI as I did in the related story, above.
> The shielded loop is untuned. The MFJ relies only on VHF noise. In some
> cases, an ultrasonic microphone at the focus of a small parabolic or
> spherical reflector is good at finding coronal discharges as well as active
> arcs and discharges. MFJ also makes that at a reasonable price.
>
> Our power provider was out the next day to fix the problem. We even gave
> them the pole number which is a great help to any power provider.
>
> Dave - WØLEV
>
> On Mon, Mar 22, 2021 at 2:28 AM Kim Elmore <cw_de_n5op@sbcglobal.net>
> wrote:
>
> > It's odd that you can't hear it on your portable rx. That made me
> > curious: What if this is something internal to your '847? Have you tried
> > pulling your '847 and listening on a different receiver using the same
> > antenna? If you have, do you still hear the noise? It's a long shot,
> but...
> >
> > Kim N5OP
> >
> > On 3/21/2021 7:28 PM, Gary wrote:
> > > Mike,
> > >
> > > Thanks for the info. I understand locating the noise
> is
> > more important than identifying the noise. I am just try to play all the
> > angles as I was hoping to work the WPX contest nest weekend. I have been
> > walking the neighborhood a good chunk of the afternoon, and have not been
> > able to hear the noise on my portable shortwave and loop antenna. It is
> as
> > strong as ever on my home station.
> > >
> > > I have an MFJ 852 Noise Finder and it seems to go
> crazy
> > when broadside to any house. The neighbors on each side of me drive the
> > meter full scale.
> > >
> > > Yep I only want to knock on one door, as I know that
> > can get dicey. I would rather place a call to a utility, but can’t really
> > do either until I know.
> > >
> > > Keep the suggestions coming!
> > >
> > > Thanks and 73,
> > > Gary “Joe” kk0sd
> > >
> > > From: Mike Martin <mike@rfiservices.com>
> > > Sent: Sunday, March 21, 2021 6:53 PM
> > > To: Gary <gary_mayfield@hotmail.com>
> > > Cc: rfi@contesting.com
> > > Subject: Re: [RFI] New Interference at kk0sd
> > >
> > > Joe I haven't had time to read all the other input but I can tell you
> it
> > is not an arcing source or a sparking source. either one of the two would
> > be much broader than what you're reporting. if someone were to tell you
> > exactly what it is you really wouldn't be any further ahead. You would
> > still have to find which residents or business it's in. My suggestion
> would
> > be to either go mobile or on foot, preferably on foot listening to the
> > frequency that you know the problem affects. once you locate the
> residents
> > then go through the breaker scenario and locate what the source is. Be
> 100%
> > certain of the structure or home that the problem is in before knocking
> on
> > the door. The last thing you want to do is start guessing. Guessing we'll
> > ruin the relationship with your neighbors.
> > > Be safe,
> > > Mike k3RFI
> > > www.rfiservices.com<http://www.rfiservices.com>
> > > Get BlueMail for Android<http://www.bluemail.me/r?b=16696>
> > > On Mar 21, 2021, at 2:01 PM, Gary <gary_mayfield@hotmail.com<mailto:
> > gary_mayfield@hotmail.com>> wrote:
> > >
> > > My last problem was tracked down to a neon sign in a neighbors garage.
> I
> > had several months of blissful relatively low noise operation, but now
> have
> > a new RFI issue.
> > >
> > > You can see a recording of it here:
> > > https://www.youtube.com/watch?v=GKf4P44FXMo
> > >
> > > I have turned all of the breakers in my home off and run the radio from
> > a battery and the noise remains.
> > >
> > > My neighborhood utilities are all underground.
> > >
> > > There are no solar installations in my neighborhood, and the noise is
> > there at night anyway...
> > >
> > > The noise is not detectable on the AM broadcast band, but starts around
> > 2 MHz and runs to at least 6 meters.
> > >
> > > It is there 7 days a week 24 hours a day.
> > >
> > > It is not detectable from my pickup when I drive the streets of my
> > neighborhood (checking both AM broadcast and Shortwave).
> > >
> > > If any one has heard something like this, I would love to hear what you
> > found.
> > >
> > > Thank You for your input and help!
> > >
> > > 73,
> > > Gary "Joe", kk0sd
> > >
> > >
> > > ________________________________
> > >
> > > RFI mailing list
> > > RFI@contesting.com<mailto:RFI@contesting.com>
> > > http://lists.contesting.com/mailman/listinfo/rfi
> > > _______________________________________________
> > > RFI mailing list
> > > RFI@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/rfi
> > --
> >
> > Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP
> > SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)
> >
> > /"A great second violinist plays second fiddle to no one." //– Robert C.
> > Marsh, Chicago Sun-Times./
> >
> > _______________________________________________
> > RFI mailing list
> > RFI@contesting.com
> > http://lists.contesting.com/mailman/listinfo/rfi
> >
>
>
> --
> *Dave - WØLEV*
> *Just Let Darwin Work*
> _______________________________________________
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>
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