Hi Richard,
I never stop thinking, and you originally said you were encountering 120 Hz
noise bursts but I don't know how you determined it had 120 Hz component.
As Frank mentioned the approximate 1 Hz repetition which goes away when it
rains is what one might expect with an electric fence but I would not
expect a typical repetitive electric fence discharge system (one that
discharges every second) to have a specific 120 hertz component as the
"transmitter" normally is just a capacitor charged to a very high DC
voltage which is then momentarily connected to a pulse transformer primary
to discharge the capacitor which greatly steps up the voltage to thousands
of volts (but with limited energy) so there is no specific relationship
with 120 Hz. There is likely a huge amount of harmonics generated unless
the pulse is intentionally shaped which I believe some companies are now
trying to do in order to try and limit the harmonic content. The high
voltage generation concept is similar to how a conventional Xenon tube
flash circuit works in photography. Can you upload a recording of your
noise burst so we have a better idea of what you are hearing/seeing? But
as others have said I never try and guess what the source is other than to
try and determine if it is power line related noise because if it's not
power line noise then I might not pack my vehicle with as much VHF and UHF
DF gear.
Don (wd8dsb)
On Thu, Dec 29, 2022 at 11:51 PM Don Kirk <wd8dsb@gmail.com> wrote:
> Frank,
>
> Great comment about the electric fence, and I previously dealt with an
> electric fence case at W9RE and it indeed had a rate of approximately 1
> second. It was a very brief discharge every second and if I were to
> describe it, it sounded like tick, tick, tick with each tick being spaced a
> second apart (the ticks were very brief). We were able to hear it at great
> distances just using my old car AM radio that has no noise blanker
> technology whereas it could not be heard on a modem cars radio that Mike
> W9RE had. I believe most modern car radios have noise blanker technology
> that makes them less useful for RFI detection.
>
> Don wd8dsb
>
> On Thu, Dec 29, 2022 at 11:23 PM Frank W3LPL <donovanf@starpower.net>
> wrote:
>
>> Richard,
>>
>> I forgot to mention that electric fence RFI typically has
>> a definitive repetition cycle similar to what you described
>> and often goes away during rain.
>>
>> 73
>> Frank
>> W3LPL
>>
>> ----- Original Message -----
>> From: "Don Kirk" <wd8dsb@gmail.com>
>> To: "Richard" <richard@karlquist.com>
>> Cc: "rfi" <rfi@contesting.com>
>> Sent: Friday, December 30, 2022 4:07:12 AM
>> Subject: Re: [RFI] Powerline noise question
>>
>> Hi Rick,
>>
>> Sorry that my last message was blank as I typed it on my cell phone and
>> then accidentally deleted the text prior to hitting the send key.
>>
>> You can use your MF/HF loop to do some triangulation on the source but you
>> often need to get far away from existing power lines to avoid receiving
>> conducted signals along the lines versus the signal direct from the
>> source. As an example when out in the country I will often walk out into
>> the middle of farm fields to get away from overhead power lines when
>> obtaining bearings. As you get closer to the source you can go higher in
>> frequency if it really is power line noise (arcing hardware). As an
>> example you can go to 40 meters then 20 meters and then 10 meters as you
>> get closer to the source as a form of attenuation and to also help you get
>> multiple wavelengths away from objects that might otherwise skew your
>> readings. Adjustable RF gain and/or attenuators are also very helpful.
>>
>> If it really is power line noise (arcing hardware) you should be able to
>> hear the source using an AM receiver with a 3 or 4 element yagi when you
>> are within approximately 0.25 miles of the source (and sometimes upto 0.5
>> or more miles away). Make sure the yagi is tuned for the frequency you
>> are
>> using in order to assure the correct antenna pattern. When you get very
>> close to the suspect pole you will typically need to throw in 20 to 30 dB
>> of attenuation in order to determine the exact pole (in rare cases you
>> might even need 40 dB of attenuation).
>>
>> One thing that is great is that it sounds like your source has a specific
>> pattern that will help you differentiate it from other sources but if the
>> pattern is always a very specific 0.9 second pattern that never changes
>> regardless of what day you listen, etc. that makes you wonder if something
>> else is going on, but the fact that it goes away when it rains is
>> typically
>> a good indicator that it's indeed power line noise (arcing hardware).
>>
>> Don (wd8dsb)
>>
>> On Thu, Dec 29, 2022 at 10:46 PM Don Kirk <wd8dsb@gmail.com> wrote:
>>
>> >
>> _______________________________________________
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>> http://lists.contesting.com/mailman/listinfo/rfi
>>
>
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