Hi Mike, Gary, and gang,
Well after seeing Garys shielded un-tuned loop, I watched the video on how
to build that loop. I just built one almost identical to his loop but used
RG-58 coax since that's what I had on hand. I also spent 10 seconds
building a simple 1 turn 9 inch loop (no form, just free standing) for
comparisons which is even smaller than Garys loop, and I can tell you there
is no comparison. Without doing any impedance matching, the 9 inch
un-tuned single turn loop I built has a gain that is approximately 23 dB
greater than Garys loop when tested in the AM broadcast band and it still
exhibits nice nulls which comes as no surprise. My single turn non
shielded loop just has about 6 inches of twisted wire (the same wire that
forms the loop) to form the feedline to it, and then I just used a 3 foot
piece of 50 ohm coax to connect it to my receiver. I used the same 3 foot
piece of coax to connect the shielded un-tuned loop to the receiver. While
my un-tuned 9 inch loop might not be as well balanced (one null might be
deeper than the opposite null), it makes one fine DF antenna in a pinch.
Also if Gary needs more gain he can just make the loop I made bigger in
diameter. It really just takes seconds to make this antenna (much less
than a minute).
I now fully understand why Gary can't hear his noise, as his un-tuned
shielded loop has very poor sensitivity based on my trying to copy the
design. While I normally use preamps with my DF loops, Garys RFI is so
strong that I'm pretty darn sure he can make a simple one turn loop to
figure out what possible directions the signal is coming from. Something I
have done in the past is to use a cardboard box as the antenna form as it
does not have to be round. Need to figure out what directions the signal
is coming from before leaving his property if at all possible.
Just my opinion, and I will try and post some comparison videos but they
will not be pretty as I'm buried in other tasks.
73,
Don (wd8dsb)
On Tue, Mar 23, 2021 at 8:33 AM Mike Martin <mike@rfiservices.com> wrote:
> Remember in his shack he has a very good radio and a very good antenna
> which together increased sensitivity and allow him to hear much further
> away. when he goes outside with a portable and a smaller antenna he doesn't
> have the sensitivity he had inside there for he may have to travel a lot
> further before he's able to receive it.
>
> Be safe,
> Mike
>
> Get BlueMail for Android <http://www.bluemail.me/r?b=16696>
> On Mar 22, 2021, at 11:37 PM, Gary <gary_mayfield@hotmail.com> wrote:
>>
>> Kim,
>>
>> I hear it on the portable when connected to the vertical antenna, but will
>> undertake an antenna substitution experiment this weekend.
>>
>> Keep the suggestions coming!
>>
>> 73 and Thanks,
>> Gary "Joe", kk0sd
>>
>>
>>
>> -----Original Message-----
>> From: RFI <rfi-bounces+gary_mayfield=hotmail.com@contesting.com> On Behalf
>> Of Kim Elmore
>> Sent: Monday, March 22, 2021 4:44 PM
>> To: Don Kirk <wd8dsb@gmail.com>
>> Cc: Rfi List <rfi@contesting.com>
>> Subject: Re: [RFI] New Interference at kk0sd
>>
>> That’s a great idea, too! I once ran into an interference problem that was
>> inherent to the antenna, but only under certain conditions. It didn’t sound
>> like Gary’s but I pulled a lot of hair out fixing that one. I’m simply
>> suspicious that he hears NOTHING with his portable rx so I’m after
>> eliminating anything inherent to his station. Standing by his vertical with
>> his portable rx is a great idea.
>>
>> 73,
>>
>> Kim N5OP
>>
>> "People that make music together cannot be enemies, at least as long as the
>> music lasts." -- Paul Hindemith
>>
>> On Mar 22, 2021, at 2:24 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*
>>>> ------------------------------
>>>>
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>>>>
>>> ------------------------------
>>
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