[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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