Hi Joe,
I revisited the AM radio with internal bar antenna today on a known faulty
power pole (bad lightning arrestor which is scheduled for replacement). I
used two different AM radios (one was an Eton and the other was a Sony
Walkman Sports which has a very sensitive receiver and both have internal
bar antennas that have very sharp nulls). While the Sony worked best, I
could not hear the RFI from this faulty pole when I got over 150 feet from
the pole with the AM radios while I could detect the RFI from over 0.2
miles away on 136 MHz and at a much greater distance on 80 meters as an
example. The AM radio with internal bar antenna was really useless until I
was standing very close to the pole (within approximately 25 feet), and
then I was able to detect a very distinct null when pointed up at the top
of the pole where the bad arrestor is located but it had to be pointed in
exactly the right direction to detect the null. While it did have an
amazing null when up close, it really was of no help to me in finding the
pole because I had to use 136 MHz to get me there. You could hear the
noise with the AM radios at a much greater distance when standing under the
lines but that's due to the signal propagating down the lines which is
something you can often observe while driving your car down the road.
As I mentioned offline to you there are many times where I can hear bad
power poles on a specific band (like on 80 meters but not on 160 or 40
meters) when located far from the pole which initially came as a surprise
to me but one that I now understand and accept. This phenomena in itself
shows why the use of higher tech gear than a AM radio with internal bar
antenna is often required and if you have the higher tech gear it really
makes life much easier and the high tech gear normally involves a radio you
already own and a home made antenna.
Just my opinion based on many hours of tracking down RFI for myself and
others.
73, (wd8dsb)
Don
On Wed, Jan 13, 2021 at 9:59 AM Joe <nss@mwt.net> wrote:
> I have used all sorts of direction finding stuff. From 2 meters Fox hunt
> stuff, to the 138~ Mhz AM yagi and scanner.
>
> BUT what I still find to be the absolute best is the simplest, And if
> you don't already have one, you probably can get one for like 5 bucks!
> The simple old portable AM reciever. You know the 550 to 1700 Khz
> Broadcast band,. The old farts would say the Transistor Radio.
>
> That ferrite bar antenna has nulls off the end that are like infinite
> deep. and extremely narrow. I'd wager the nulls 3 db points are only a
> degree or two wide. Lets see you get that kind of accuracy with a 4
> element beam on 2 meters.
>
> I was helping a local try to find a noise on his farm that was totally
> killing his HF, 20+ db over most times. He has tried the as described
> above (not the AM radio I think he thought I was full of something you
> find a lot of on a farm when i suggested the AM Radio)
>
> He just could NOT find the source. He did not even think it was on HIS
> farm. I drove my car first listening to an empty spot on the AM radio
> and when I started hearing the noise I got out and used the little
> radio, got a beam heading, or should I say NULL heading, I was probably
> almost a mile from his house it's that bad!
>
> drove 1/2 way towards his place took a nother reading and drew it on the
> map. well I see where they are crossing
>
> I do it a few more times even past his place and it all points to his
> place.
>
> I park in his driveway get a null and walk in it's direction. it's LOUD!
>
> But in less than 5 minutes I'm standing next to a silo, and a wire that
> is going underground somewhere. the Null is incredible when I am even
> only inches away from that wire if it is off the ends of that ferrite
> bar there is no noise but move 1/2 a inch away from that wire in a side
> to side sweep and BOOM BBBZZZZZZZZZZZZZ.
>
> It is incredible the accuracy!
>
> Joe WB9SBD
>
> On 1/13/2021 12:11 AM, K9MA wrote:
> > I haven't tried using an antenna with a sharp null, but I wonder how
> > well it really works with power line noise. The problem seems to be
> > that the lines themselves radiate so much that it often appears that
> > the noise is coming from some distance away from the true source. What
> > sort of experience have others had?
> >
> > I like the idea of the 135 MHz Moxon, though. It would be a lot
> > smaller than the yagi on the MFJ-856, too.
> >
> > 73,
> > Scott K9MA
> >
> > On 1/12/2021 3:25 PM, N4ZR wrote:
> >> Using a Moxon antenna is another way to get a sharper null - there
> >> was an article in QST describing such an antenna, which I use with a
> >> shirt-pocket handi-talkie with 136 MHz AM aircraft band. The null
> >> off the back is deep and narrow.
> >>
> >> 73, Pete N4ZR
> >> Check out the new Reverse Beacon Network
> >> web server at <http://beta.reversebeacon.net>.
> >> For spots, please use your favorite
> >> "retail" DX cluster.
> >>
> >> On 1/12/2021 1:41 PM, David Eckhardt wrote:
> >>> Most recently, I have isolated a source on a power pole by using
> >>> both the
> >>> MFJ device AND a home brew 0.5-meter shielded loop connected to a
> >>> battery-powered receiver tuned to the frequency of maximum RFI. The
> >>> null
> >>> perpendicular to the loop plane is extremely sharp and, from that
> >>> experience, I dare say sharper than the MFJ device or at least an
> >>> equal.
> >>> Another strength of the shielded loop is that you can isolate the
> >>> source
> >>> *at* the interfering frequency(ies). Also, confirming a source
> >>> with two
> >>> entirely different technologies can be helpful in nailing the source.
> >>> Once isolated, our power provider, PVREA (N. Colorado), had the problem
> >>> fixed the next day and waited for us to confirm their fix. Not all
> >>> providers are so responsive.
> >>>
> >>> Dave - WØLEV
> >>>
> >>> On Tue, Jan 12, 2021 at 1:25 PM Dave Cole <dave@nk7z.net> wrote:
> >>>
> >>>> Hello,
> >>>>
> >>>> I have some RFI location information at:
> >>>>
> >>>> https://www.nk7z.net/i-have-rfi-now-what-locating-it/
> >>>>
> >>>> I use the MFJ-856, (https://mfjenterprises.com/products/mfj-856),
> when
> >>>> looking for VHF RFI. It will pinpoint an RFI source and in most cases
> >>>> you can tell which part of the house the RFI is coming from, if you
> >>>> are
> >>>> on the sidewalk in front of the home.
> >>>>
> >>>> Your RFI could be anything, is it on a schedule, does it change
> >>>> strength, lots of questions to answer first.
> >>>>
> >>>> IDing via signature can sometimes work, (not too often), but
> >>>> nothing has
> >>>> worked for me better than getting out on foot and looking for the RFI
> >>>> source.
> >>>>
> >>>> Once you have it located that is another entirely different matter.
> >>>>
> >>>> 73, and thanks,
> >>>> Dave (NK7Z)
> >>>> https://www.nk7z.net
> >>>> ARRL Volunteer Examiner
> >>>> ARRL Technical Specialist, RFI
> >>>> ARRL Asst. Director, NW Division, Technical Resources
> >>>>
> >>>> On 1/11/21 8:45 PM, RALPH GRANCHELLI wrote:
> >>>>> Hello inteference investigators,
> >>>>>
> >>>>> I have new RFI issue that started about a week ago.
> >>>>>
> >>>>> I have eliminated the house / items as a source.
> >>>>>
> >>>>> Killed all breakers, ran the XCRV from batt. No change.
> >>>>> Disconnected ext
> >>>>> antenna, used in house antenna and no noise. So noise coming in
> >>>>> from ext
> >>>>> antenna.
> >>>>>
> >>>>> The RFI is strongest on 80 meters however it is present up to vhf
> >>>>> with
> >>>>> diminished magnitude.
> >>>>>
> >>>>> I took a screen shot of it on the spectrum scope.
> >>>>>
> >>>>> Does anyone recognize the signature?
> >>>>>
> >
>
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