[RFI] Nest Thermostat - Think about this

Dale svetanoff at earthlink.net
Tue Dec 3 23:35:49 EST 2013

All who have posted on the thread ...

Folks, before any given t'stat unit is praised or condemned, consider that EACH installation is different.  Yes, some may have better RFI protection than others, but keep in mind the basic principles that govern the situation:

1.  RF field strength produced by the source (antenna + xmtr power)

2.  Distance between source and victim (t'stat or other controller)

3.  Threshold of malfunction of the victim (a combination of field strength and frequency + the size of the victim's antenna [the wiring between the t'stat and the HVAC system and/or the Internet connection - if wired])

Remember: ALL silicon junctions will go into forward conduction at about 0.6 to 0.7 volts (self-rectified from applied RF).  I suspect that some units on the market have a degree of RF immunity designed in, but probably not all makes and models do, and the tolerable limit may be quite small.  The wiring between the t'stat and the HVAC unit is the antenna (unless the t'stat also has AC power and the Internet connection applied to it via a separate wired feeds - then it has 2 or 3 antennas).  RF choking needs to be applied to BOTH ends of each "antenna", as the HVAC internal controller or the switch/router could malfunction just as much as the t'stat.  See the K9YC info (posted many times on this reflector) for how to address the RF cleanup.

The villain in all of this seems to be the ham antennas.  Those located close to the house (whether alongside or above) are the worst cases.  One "cure" could be to either move the antennas further away or reduce xmtr power (NOT what you want to hear).  However, for anyone who has a t'stat that goes nutsy with RF applied, try this experiment: if possible, use the antenna that causes problems and then reduce power in 10dB steps.  Start at QRO levels (say 1000 watts), then go down to 100 watts, then 10 watts, then 1 watt, if possible.  If you hit a power level that no longer causes RFI to the t'stat, you have found the "threshold of pain" for that unit.  

In general, if you either move the antenna further away OR don't exceed the threshold power level OR apply RFI suppression to the t'stat wiring, you should be OK.  You need to do at least one of the above, or try another brand/model of unit.  If you have no problems with your unit (as seems to be the case for Jim, below), then count yourself lucky.  My electronic t'stat is a Robertshaw, but it is not remotely controllable.  Most of my HF antennas are at least 100 feet from the house, with the main radiating parts even further out.  Thus, my t'stat is "great" because it does not malfunction when I operate.  The problem is that I have no clue what it would do if there was a 1000 watt signal within 20 feet of the unit.  

Bottom line: it is very difficult to say what any given device will do in the presence of strong RF fields.  Thus, when buying a unit, make certain that you can return it if it malfunctions.  Lacking that, contact the manufacturer (or their rep) PRIOR to installation and see what they say about RF and their product.  Good luck.

73, Dale

-----Original Message-----
>From: James Chaggaris <jimc at pwrone.com>
>Sent: Dec 3, 2013 2:49 PM
>To: rfi at contesting.com
>Subject: Re: [RFI] Nest Thermostat
>Had a Nest (Ver 2) at my old QTH and never had an issue with RF even when
>running full power.  Tower was about 50' away and I also had a windom
>running over the house.
>Jim N9WW
>James Chaggaris
>PowerOne Corp./PowerOne Environmental
>2325 Dean St. Suite 200
>St. Charles, IL 60175
>Phn: 630.443.6500
>Cell: 630.669.2241
>Fax: 630.44366505
>Website: www.pwrone.com <http://www.pwrone.com/>
>On 12/3/13 2:22 PM, "David Cole" <dave at nk7z.net> wrote:
>>Well...  That crosses off a Nest Thermostat from my list of cool geeky
>>things to own...  I had actually been thinking about one...
>>Thanks and 73's,
>>For equipment, and software setups and reviews see:
>>for MixW support see;
>>for Dopplergram information see:
>>for MM-SSTV see:
>>On Tue, 2013-12-03 at 15:15 -0500, Larry Bryan wrote:
>>> Problem is they refuse to send another base and without it, the stat
>>> won't work. 
>>> 73
>>> Larry - W8LIG
>>> On Tue, Dec 3, 2013 at 2:29 PM, David Cole <dave at nk7z.net> wrote:
>>>         If it were mine, I would bypass it for RF.  A call to Nest
>>>         letting them
>>>         know it is living in a high RF environment might be in
>>>         order...
>>>         Also, you might want to run some exposure calculations as
>>>         well...  :)
>>>         --
>>>         Thanks and 73's,
>>>         For equipment, and software setups and reviews see:
>>>         www.nk7z.net
>>>         for MixW support see;
>>>         http://groups.yahoo.com/neo/groups/mixw/info
>>>         for Dopplergram information see:
>>>         http://groups.yahoo.com/neo/groups/dopplergram/info
>>>         for MM-SSTV see:
>>>         http://groups.yahoo.com/neo/groups/MM-SSTV/info
>>>         On Tue, 2013-12-03 at 13:09 -0500, Larry Bryan wrote:
>>>         > I bought a NEST programmable thermostat in 2012 so I could
>>>         monitor the
>>>         > house while in Florida. It's worked very well until last
>>>         month. I was
>>>         > working 40m and after I was done, the wife wanted to know
>>>         why the HVAC was
>>>         > running and cold air coming out of the floor vents. I
>>>         investigated and
>>>         > found that both the AC and Heat was running and the
>>>         thermostat was showing
>>>         > the wrong temperature.
>>>         >
>>>         > Calling NEST the next day, I was informed that the base of
>>>         the thermostat
>>>         > has fusing and the fuse was blown. NEST sent a replacement
>>>         base and after
>>>         > installation, it was working again.
>>>         >
>>>         > Again last night while working a DXpedition on CW, I shut
>>>         down and walked
>>>         > into the family room to find the same thing had happened. My
>>>         SteppIR is on
>>>         > a tower directly adjacent to the house and it was raised to
>>>         about 35 feet.
>>>         >
>>>         > So I'm looking for suggestions on how I can reduce the RF
>>>         getting into the
>>>         > thermostat. Obviously going back to an analog thermostat is
>>>         a solution but
>>>         > would like to make that the final solution if possible.
>>>         > 73
>>>         > Larry - W8LIG
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