[RFI] Multi-Stage High Efficiency Air Conditioner Units

[Jim Brown]

On 2/17/2020 7:10 PM, Kim Elmore wrote:
> It seems that I may have used the wrong terminology, as the latest 
> approach to this is "variable speed compressor," where the compressor 
> speed is varied. Looking briefly into this, I found that some companies 
> tout that they do this with an inverter. apparently, AC input is 
> rectified, possibly filtered, then converted to variable frequency AC, 
> which is used to control the compressor speed. Depending on how that's 
> done, it sounds like it could either be RFI-silent, or a catastrophic 
> screamer.

Yep, that's how 99.9% of variable-speed motor controllers work. You'll 
find this addressed in this app note that ran in NCJ a few years ago, 
and my older RFI tutorial. http://k9yc.com/KillingReceiveNoise.pdf
k9yc.com/RFI-Ham.pdf

> I have a bid on a Carrier system -- does anyone have experience with 
> variable-speed Carrier units? Does anyone have contacts at Carrier that 
> I could talk to about any RFI associated the units that have been 
> specified in the bid and what measures might need to be taken?

Most better mfrs can sell you an RFI kit, that may or may not make the 
unit quiet. Without that kit, the system (controller and motor) is 
likely to be quite noisy. Last week, I saw a post from a ham who got the 
RFI kit for his system, but it didn't solve his problem. A ferrite choke 
on the wiring to the thermostat did. Both the kit and the choke were 
required.

73, Jim K9YC