I failed to mention that the manufacturer, Lennox, specifically suggests
using a *shielded* thermostat cable.
"IMPORTANT . . . We highly recommend using 18 - 22AWG shielded thermostat
cable for communications terminals . . . which will help eliminate any
noise interference."
This comes from Lennox's iComfort S30 Ultra Smart Thermostat Installation
and Setup Guide, 507536-08 8/2020.
~ Alan
On Thu, Nov 11, 2021 at 7:33 AM Don Kirk <wd8dsb@gmail.com> wrote:
> 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
>> _______________________________________________
>> RFI mailing list
>> RFI@contesting.com
>> http://lists.contesting.com/mailman/listinfo/rfi
>>
>
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