Attached is the 0.5-Meter shielded loop I built for DFing and ELF reception
(in addition to the 2-Meter shielded loop I have up on the hillside). It's
pretty simple.
Dave - WØLEV
On Mon, Mar 22, 2021 at 7:24 PM Don Kirk <wd8dsb@gmail.com> wrote:
> 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*
>> _______________________________________________
>> RFI mailing list
>> RFI@contesting.com
>> http://lists.contesting.com/mailman/listinfo/rfi
>>
>
--
*Dave - WØLEV*
*Just Let Darwin Work*
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