[R-390] High Electrical hash noise level

David Wise David_Wise at Phoenix.com
Tue Mar 29 16:28:38 EDT 2011


That's what I did.

Dave Wise

>-----Original Message-----
>From: r-390-bounces at mailman.qth.net 
>[mailto:r-390-bounces at mailman.qth.net] On Behalf Of Steve Toth
>Sent: Tuesday, March 29, 2011 9:16 AM
>To: r-390 at mailman.qth.net
>Subject: Re: [R-390] High Electrical hash noise level
>
>
>
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>Curt
>I did a little scanning on the net for info on Pulse Width 
>Modulation  and you are probably correct about the use of a 
>PWM drive.  I still haven't heard from Trane or the Dealer but 
>from my very limited knowledge of PWM and what I found on the 
>net, it appears what Trane is using is a Direct Torque Control 
>PWM controller on their fan inducer motor.  From what I read, 
>this type of PWM is directly related to Delta PWM that 
>generates a full spectrum noise (no particular harmonics) 
>sawtooth wave shaped into an AC voltage sine wave format 
>within certain limits and is used to drive AC motors.  This 
>would explain the hash all over the spectrum.
> 
>Also, you can actually hear the pitch of the noise change 
>(which I would think would be the changing of the sine wave 
>format) as, from what I would guess, is the controller 
>calculating the changes for the characteristics of the motor 
>voltage to match the fan's load prior to the main furnace 
>blower turning on. 
> 
>You know, this is actually kind of like an ignition noise 
>problem from the days when we had contact point ignition 
>systems that generated interference in our car AM radios.  A 
>viable solution to this might be in my 1964 ARRL Radio 
>handbook!  If I remember correctly it was basically 1.) bypass 
>every wire in sight, 2.) shield every wire in sight, and 3.) 
>thoroughly ground the shields.
> 
>Which, when you think about the age of the R390A is sort of 
>actually appropriate in an ironic sort of way....
> 
>And, of course, the simplest solution is just turn off the 
>furnace when I have my radio equipment on the air!  ; - )
>


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