Here is yet one more thing I failed to mention in earlier parts of this
thread . . .
The furnace manufacturer's thermostat "Installation and Setup Guide" says:
"Reducing Electrical Noise . . . Keep all [thermostat] communication wiring
as far away from the house electrical wiring and large electrical
appliances as possible. Recommended minimal distance is 15 feet.*" *
In my case, the wiring between the furnace and thermostat had been bundled
with AC cables through some holes in the studs.
~ Alan
On Thu, Nov 11, 2021 at 8:54 AM Alan Higbie <alan.higbie@gmail.com> wrote:
> 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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