Re: you can fry a Nest thermostat - on the RFI hunt

Dan Pflugrath


Palomar Engineers is a good source of EMI/RFI countermeasures information and products.  In the case of your Nest Thermostat, all lines going into and out of that control will need to have a mix 31 countermeasures applied.  Mix 31 for 1-300 MHz (suitable for most HF amateur and commercial transmitters)  These can be torrid cores with the wiring making multiple turns through the core or snap on cores etc.  Depending on the frequency you may need mix 75  0.15 to 10 MHz.


Good luck, your are on the right track to reduce your noise problem.







-----Original Message-----
From: [] On Behalf Of Shawn / K7ATA
Sent: Monday, September 14, 2020 11:09 AM
Subject: Re: [SnoVARC] you can fry a Nest thermostat - on the RFI hunt


First thing to do is put RFI filters on ALL of the control runs

connected to the nest; this SHOULD eliminate a lot of its radiated

noise, and will probably protect it some as well.


Common mode chokes with bypass capacitors would be my first step.






On 9/14/2020 10:26 AM, Ryan - KJ7GIE wrote:

> Wanted to share this bit of info I've run across in my hunt for RFI in my house. Using an AM radio I noticed my Nest Thermostat was _very_ noisy. There is also no way to turn the thermostat off; it will simply drain the battery and then shut itself down which is the only way to actually get the thing to go off. But, I also identified, as I was hunting online, more than a few people have fried their Nest Thermostats on 40 meters. I guess running a long wire, from HVAC to thermostat, and then filling the thermostat with tiny fuses and FETs just doesn't play nice with amateur radio.

> So, I've got this source of RFI in my house I cannot turn off that is connected to a long wire that _may_ resonate / couple to 1 or more of the HF bands. How lucky can a guy get?

> Additionally... I _know_ the HVAC itself is noisy as it impacts my 70cm performance! Has anyone else gone to this extreme to fix it?

> It's easy enough to turn the HVAC (blowers / condenser etc.) off while I'm operating. But the Nest is still active so I'm still on the hunt for ways to reduce / eliminate that issue (without replacing the unit as I really like my Nest thermostat). This is also pushing me towards the "wire on fence" outside HF antenna design and _not_ using a wire in the attic. My HVAC is in the attic so an attic based solution is looking less and less like a good use of my time.






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