Richard,
One last comment. I guess an electric fence might also use ac just stepped
up along with a current limit resistor and then just have it active for a
brief amount of time every second to allow an animal to break free but I’m
not familiar with those systems if they exist.
I am curious to hear your RFI burst if you can upload a recording of it.
Don
On Sat, Dec 31, 2022 at 11:55 AM Don Kirk <wd8dsb@gmail.com> wrote:
> 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:
>>>
>>> >
>>> _______________________________________________
>>> RFI mailing list
>>> RFI@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/rfi
>>>
>>
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