Hi Alan,
Great write up, and very timely. This past weekend a fellow ham asked what
he could do to eliminate RFI that was being generated by his furnace, and I
forwarded your write up to him to help provide some ideas on how he should
proceed.
Also thanks for testing out my circuit breaker sniffing technique, and glad
it resulted in positive results. This technique has been very helpful to
me as a first step when trying to locate what electrical circuit within a
house or commercial building the RFI is coming from. It really works
better than I ever imagined.
73,
Don (wd8dsb)
On Wed, Nov 10, 2021 at 2:13 PM Alan Higbie <alan.higbie@gmail.com> wrote:
> I just had a successful outcome with RFI from a new Lennox furnace we
> installed 3 weeks ago. It is a Lennox SLP99UHV gas furnace.
>
> When running, it generated noise which was *8 dB* up from the previously
> measured 80 meter noise floor. Similar on 7 MHz - but not much on higher
> bands.
>
> The furnace has a wi-fi enabled thermostat control (Smart Hub) which lets
> me turn the furnace on and off with an iPhone app while sitting at the rig
> watching the noise floor of the P3 / SVGA display.
>
> With help from RFI reflector and deep research on the manufacturer's
> website - I found that Lennox has an EMI Filter Kit *604552-1*. The "kit"
> was back ordered through the manufacturer - but the parts were readily
> available from Mouser.
>
> The kit is also called a "Line Suppression Kit."
> Here is link:
> https://www.lennoxpros.com/604552-01-kit---line-suppression/p/54W22
>
> Kit consists of a CorCom 12EP1 AC line filter, wires, connectors and some
> snap-on chokes. Plus, we added shielded thermostat wire.
>
> Lennox has instructions for installing the kit. The instruction sheet (2
> pages) was difficult to locate, but for reference it is numbered *507153-01
> *and titled *"Installation Instructions for Electromagnetic Interference
> Kit (604552-01) For Use with 90% Efficiency Modulating and Variable
> Capacity Furnaces." *
>
> Fixes installed:
> 1. Installed AC line filter - mounted inside the furnace - directly on the
> blower housing (using self tapping screws)
> 2. Replaced existing unshielded thermostat wiring (approx. 40 feet long)
> with SHIELDED CABLE.
> 3. Placed #31 toroids (with 5 turns) close to the ends of the thermostat
> cable.
> 4. Place #31 snap-on ferrite on wire coming from the supply junction box.
>
> This furnace had been newly installed - so I used the original authorized
> installer. This will avoid potential warranty issues down the road.
>
> Results:
> Furnace RFI now completely gone - and noise floor back to where it was.
> Now it makes no difference if this furnace is operating or not.
>
> Also, this was the first time I used the WD8DSB Breaker Panel Sniffer
> method. Before installing the furnace fix, I followed 'DSB's method shown
> on YouTube:
> https://www.youtube.com/watch?v=vDB8rAwVt5Y&t=146s
>
> Double-blind research: Closed both my eyes and slowly moved the loop up and
> down the panel until I heard high noise on a portable shortwave receiver
> (Tecsun PL660). Then I opened both eyes and read the breaker's label:
> "Furnace." After the furnace fixes - I repeated the Panel Sniffer Test:
> and now, absolutely no RFI at the panel.
>
> Thanks to all who have contributed knowledge and experiences re: furnace
> RFI here on the reflector and the ARRL RFI pages.
>
> 73, Alan K0AV
> _______________________________________________
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> RFI@contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
>
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