Re: [RFI] RFI from furnace/air conditioning

[Jim Brown <jim@audiosystemsgroup.com>]

Great diagnosis and great advice, Randy.

Variable speed motor controllers are notorious sources of RF noise.  The 
drive to the motor is a modulated rectangular wave, so it's the wiring 
carrying that current that's the thing to choke first.
It's also always a good move to call the mfr and tell them to fix it. 
Some major mfrs have figured this out and can send you either a mod kit 
or a filter.
73, Jim K9YC

On 11/2/2018 5:07 PM, Randy Standke wrote:
> I don't know about Lennox in particular, but I was getting RFI from a Carrier 
> furnace.  It had a variable speed motor.  I could see the RFI change as the 
> motor ramped up to speed.  The first thing I did was add a power line filter 
> inside the unit.  This only helped a little.  What eliminated the remaining RFI 
> was running the thermostat cable through some Type 31 ferrite right at the 
> unit.  That cable was about 20 feet long and made a good antenna for the 
> conducted RFI on it.  In summary, suspect filtering may be needed on all wires 
> connected to the HVAC unit.
>
> 73,
>
> Randy KQ6RS
>
> -----Original Message-----
> From: RFI <rfi-bounces@contesting.com> On Behalf Of D C _Mac_ Macdonald
> Sent: Friday, November 2, 2018 4:05 PM
> To: RFI Group <rfi@contesting.com>
> Subject: [RFI] RFI from furnace/air conditioning
>
> I have fairly recently gotten back on the air after a few years off.  This is 
> AFTER I had to have our HVAC replaced.  It is a Lennox SL280UH090V48B-03 which 
> is a variable BTU and variable speed fan system.  Lots of trash, especially on 
> 20 meter band.  Does anyone here have experience with Lennox systems in general 
> or my specific unit ?
>
> 73 de Mac, K2GKK/5​
> (Since 30 Nov '53)​
> Oklahoma City, OK​
> USAF Retired 61-81​
> FAA Retired 94-10
>
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