[AMRadio] HVAC RFI Question

Jim Candela jcandela at prodigy.net
Fri Aug 11 12:30:37 EDT 2017


    The new system is mostly in, but duct work continues. Good news and 
bad news. The good news is that overnight the humidity dropped to 50%, 
and the "comfort feel" was really good. The new thermostat has a setting 
for humidity, and it will be set to 55%. There will be some level of 
ventilation ongoing to maintain that, so the temp and humidity should 
not be going up and down like it would with a conventional system which 
has two modes, ON, and OFF.

    The bad news is RFI, but not sure yet. The AC system is at one end 
of the home, and the Ham antenna is at the other end. The house is 1 
level Ranch style, so it is a good distance between the AC and the Ham 
antenna. I have a little Sony portable in the master bathroom "reading 
room" (not far from AC), and I can say that some of the local BS 
stations are blocked (1370AM), as is 80m, 40m..Not good. Looks like I 
have some work to do. Sigh...



On 7/29/2017 6:02 PM, Alan Victor wrote:
> Sure Jim.
> I doubt seriously that you will find a statement on a microprocessor 
> based HVAC system that it will tolerate 2 kW of RF and the associated 
> RF voltage swings that may occur across 3.6 V logic! Get you bag of 
> magic tricks out if you see this happen. On the other hand, if you 
> plan the antenna system and feed line properly you may never see an 
> issue. Bottom line from my experience, try to get the antenna system 
> as far away from the home as possible. Makes all the difference in the 
> world especially on the receive side with the IoT in the homes today! 
> Alan
> On Sat, Jul 29, 2017 at 2:26 PM, Jim Candela <jcandela at prodigy.net 
> <mailto:jcandela at prodigy.net>> wrote:
>     My old 2001 vintage American Standard AC system is conking out. I
>     am looking for a replacement, and this post is regarding HVAC
>     induced RFI into the ham bands. In order to get the SEER rating to
>     20 or above, then both the AC air ventilator & outside compressor
>     must be computerized, have variable speed motors, and even have a
>     CAT-5 cable between the units.
>     Those issues mentioned are all a red flag when it comes to RFI.
>     One quote I got was to use Lennox, XC20 Condenser, and SL280
>     furnace and air handler, cost $10125. A more traditional system
>     without the bells and whistles is about $6180. This does not
>     include the duct rework that in my case has been haphazardly
>     redone by the prior owner of the house.
>     I wonder what experience the group might have regarding the
>     various modern day HVAC systems, and HAM radio RFI. Go a step
>     further, and I could see situations where a keyed up ham station
>     might result in RF getting into the HVAC control system and
>     creating a system that is susceptible to RF.
>     JimWd5JKO
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