[RFI] Not your typical invisible fence RFI

Mon Jan 31 17:48:57 EST 2022

Here is an interesting update regarding the 20 meters broadband RFI being
generated by my neighbors Invisible Fence transmitter that's not the
typical RFI encountered with such systems.

We tried a brand new transmitter and we still had the same problem but at a
slightly higher frequency (15 MHz versus 14.3 MHz as an example), but the
frequency is very temperature sensitive (drifts based on temperature)
so hard to tell how much difference in transmitters was just due to
temperature.

We configured the transmitter for 10 KHz output versus 7 KHz output
operation, but still had the same 14 MHz broadband RFI problem.

We tried the Corcom 10VK6 transformer on the output of the transmitter, and
sure enough it eliminated the broadband RFI on 14 MHz, and a spectrum scan
from 500 KHz through 30 MHz showed everything looked great (no broadband
RFI).  Unfortunately the Corcom filter caused the invisible fence
transmitter to no longer detect a break in the in ground loop of wire, and
I had already been told that would be the case by the local invisible fence
technical manager.  This is not what I have encountered with the Innotek
brand of transmitters which still detects a break in the loop when using
the Corcom 10VK6 filter.

Also tried two #31 clamp on cores as a common mode choke on the transmitter
output wires (both wires passing through the same core 3 times and added a
second core in series with the first one in similar fashion), but this had
no effect  as the broadband RFI on 14 MHz was still present.
Note:  Now looking back at the situation I should have also tried a #31
clamp on core on each wire individually after seeing that the common mode
choke configuration had no effect.

I then wondered if I could just use a capacitor across the output of the
transmitter as a very simple low pass filter to "short out" the 14 MHz
signal while looking like an open at the 7 KHz frequency of operation.  I
decided we should start with a 0.001 uF cap since this would provide the
following inductive reactance: XL at 7 KHz = 22.7 K ohms, XL at 14 MHz =
11.4 ohms.  Low and behold this worked great in eliminating the 14 MHz RFI
and a scan from 100 KHz through 30 MHz looked great (no RFI) and my pickup
antenna was only about 5 feet from the transmitter.  We then tested the
wire break detection system on the transmitter and it still worked fine.
We also tested the distance from the in ground wire relative to when the
dog collar detected the wire, and noticed no changes in the detection
distance so the Invisible Fence technician was pleased that everything was
working just as it should.  Note: we used a 100 volt silver mica capacitor
because that's what I had on hand.  The capacitor is located between the
output of the Invisible Fence transmitter and the Invisible Fence lightning
arrestor, so hopefully the 100 volt rating will be adequate.

I'm now going to write up what we did, and then I'm going to have the local
Invisible Fence office send this info to their parent company (Radio
Systems Corporation) who is the actual manufacturer of the Invisible Fence
brand.  I want Radio Systems Corporation to officially approve the use of
the 0.001 uF capacitor for elimination of the 14 MHz broadband trash that's
generated by the transmitter.  I also want Radio Systems Corporation to
look into the design of the transmitter regarding why it's generating the
14 MHz broadband trash as it definitely generates harmful interference (The
RFI is not coming from the wall wart power supply as previously mentioned,
it's being generated by the transmitter).  I would also like to go back and
evaluate #31 cores on each transmitter output wire (high impedance on 14
MHz but not at low frequencies) as this would be a more robust solution
regarding component failure as a shorted capacitor would cause the output
signal to bypass the inground loop which would not be detected and the
homeowners dog would no longer be contained by the system which would be a
horrible situation.

In the meantime the 0.001 uF cap is in service.  Upfront I made sure that
Invisible Fence understood the homeowner must not incur any expense related
to remediation of the RFI, and they fully agreed.

Just FYI,
Don (wd8dsb)

On Mon, Jan 24, 2022 at 12:37 PM David Eckhardt <davearea51a at gmail.com>
wrote:

> My wife sez I'm always in a hurry.  Well, she is correct.  A search on the
> specific number did not yield anything.  And I did not visually search.  As
> you found, it's there.  Next time I'll slow down a bit.  Thanks for the
> verification.
>
> Dave - WØLEV
>
> On Mon, Jan 24, 2022 at 11:59 AM Hare, Ed, W1RFI <w1rfi at arrl.org> wrote:
>
>> I didn't have to do anything special, Dave. I just typed in KE3 in the
>> grantee box and scrolled down the resultant list until I saw the full ID
>> number.
>>
>> It was about 75% down the list if 116 items that KE3 has certificated.
>> Perhaps you simply overlooked it.
>>
>> I always change the default of showing only 10 items to show 500 items
>> because I don't like to have to keep clicking the "Show Next 10 Rows"
>> button at the bottom of the screen of results.
>> ------------------------------
>> *From:* David Eckhardt <davearea51a at gmail.com>
>> *Sent:* Sunday, January 23, 2022 7:52 PM
>> *To:* Hare, Ed, W1RFI <w1rfi at arrl.org>
>> *Cc:* Don Kirk <wd8dsb at gmail.com>; RFI <rfi at contesting.com>
>> *Subject:* Re: [RFI] Not your typical invisible fence RFI
>>
>> Ed, please let me know why I did not find it under the listing on the OET
>> for the FCC ID number.  That is usually where I find such things.  Please
>> educate me on how you found it.
>>
>> Dave - WØLEV
>>
>> On Sun, Jan 23, 2022 at 10:49 PM Hare, Ed, W1RFI <w1rfi at arrl.org> wrote:
>>
>> I found the certification record easily.
>>
>>
>>
>> https://apps.fcc.gov/oetcf/tcb/reports/Tcb731GrantForm.cfm?mode=COPY&RequestTimeout=500&tcb_code=&application_id=rQqvlnXl0jI%2BsFf%2Fvos1Hw%3D%3D&fcc_id=KE3-3002587
>> FCC - OET TCB Form 731 Grant of Equipment Authorization
>> <https://apps.fcc.gov/oetcf/tcb/reports/Tcb731GrantForm.cfm?mode=COPY&RequestTimeout=500&tcb_code=&application_id=rQqvlnXl0jI%2BsFf%2Fvos1Hw%3D%3D&fcc_id=KE3-3002587>
>> OET TCB Form 731 Grant
>> apps.fcc.gov
>> It is not a Class B device; it is an intentional emitter.  The rules for
>> emissions from intentional emitters, when coupled with a flawed
>> extrapolation method that the FCC defines is rather high by
>> radiocommunications standards.  The harmonic suppression required in the
>> rules is essentially 0 dB, with spurious emissions limited to the same
>> levels as would be intentional emissions on the same frequency.
>>
>> Fortunately, the cure worked.  Interestingly, ARRL has received very few
>> complaints about these, although by the look of the rules and the
>> certification test report, it looks like interference is likely.
>>
>> Ed
>>
>>
>> ------------------------------
>> *From:* RFI <rfi-bounces+w1rfi=arrl.org at contesting.com> on behalf of
>> David Eckhardt <davearea51a at gmail.com>
>> *Sent:* Sunday, January 23, 2022 1:06 PM
>> *To:* Don Kirk <wd8dsb at gmail.com>
>> *Cc:* RFI <rfi at contesting.com>
>> *Subject:* Re: [RFI] Not your typical invisible fence RFI
>>
>> There is no record on the FCC OET site for KE3-3002587 which is shown on
>> the image of the label as the FCC ID number for the wireless transmitter -
>> Part 15, Class B, Subpart B, intentional radiators.  However, if I input
>> only the Grantee Code of KE3, indeed, all kings of pet care products are
>> shown.  This might be a knockoff with a bogus FCC ID????  Also, as a Class
>> B product - home and small office - the FCC logo is required on the
>> regulatory label.  It is absent.
>>
>> Dave - WØLEV
>>
>> On Sun, Jan 23, 2022 at 3:23 PM Don Kirk <wd8dsb at gmail.com> wrote:
>>
>> > I just uploaded a video onto YouTube that documents wideband RFI on 20
>> > meters that I tracked down to my neighbors invisible fence transmitter,
>> and
>> > it's not the typical approximate 7 or 10 KHz interval RFI encountered
>> with
>> > inground invisible fences.  The RFI which is at least 150 KHz wide at my
>> > house moves around based on outdoor temperature and on warmer winter
>> days
>> > it drops down to slightly below the 20 meter band.
>> >
>> > I was hoping the problem was with the wall-wart power supply feeding the
>> > transmitter but it was not.  The transmitter has battery backup and the
>> RFI
>> > is still present with the wall wart unplugged, and we also tried a
>> linear
>> > lab grade power supply in place of the 19.0 Vdc 1 amp wall wart with no
>> > noticeable difference in the level of RFI at my house.
>> >
>> > Unfortunately the transmitter is not part of a DIY system so the
>> > manufacturer (Radio Systems Corporation) requires that we deal with the
>> > local "Invisible Fence" Dealer which is our next step.
>> >
>> > An interesting note is that when I first tracked the RFI down to my
>> > neighbors home I wound up near the main circuit breaker box.  We then
>> tried
>> > sniffing the circuit breakers with a very small loop to see what
>> circuit in
>> > the house the RFI was originating (assuming the RFI was being conducted
>> on
>> > house wiring) and this technique typically works great.  We did not
>> detect
>> > the RFI on 20 meters on any of the circuit breakers which was
>> interesting
>> > because the RFI was strong near the main circuit breaker box.  It turned
>> > out that the invisible fence transmitter is just a few feet away from
>> the
>> > main circuit breaker box which explained why the signal was strong near
>> the
>> > main circuit breaker box.
>> >
>> > For those interesting here is a link to the video documenting the RFI:
>> > https://youtu.be/rHABjR0GZWg
>> >
>> > P.S. I have great neighbors that are wonderful to work with on RFI
>> issues.
>> >
>> > 73,
>> > Don (wd8dsb)
>> > _______________________________________________
>> > RFI mailing list
>> > RFI at contesting.com
>> > http://lists.contesting.com/mailman/listinfo/rfi
>> >
>>
>>
>> --
>> *Dave - WØLEV*
>> *Just Let Darwin Work*
>> _______________________________________________
>> RFI mailing list
>> RFI at contesting.com
>> http://lists.contesting.com/mailman/listinfo/rfi
>>
>>
>>
>> --
>> *Dave - WØLEV*
>> *Just Let Darwin Work*
>>
>>
>
> --
> *Dave - WØLEV*
> *Just Let Darwin Work*
>
>