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## [RFI] What Does Variable Speed Mean?

 To: rfi@contesting.com [RFI] What Does Variable Speed Mean? Jim Brown jim@audiosystemsgroup.com Fri, 11 May 2018 12:47:59 -0700
 You have a SWITCHABLE speed motor -- it has two speeds, fast and slow.  Think of it as an DPDT switch. No electronics involved.  Think of a variable speed motor as being more like a volume control, so its speed can be varied over any value from zero to high. Except that the speed is NOT set by a pot, it's set by sending power to the motor in a train of DC pulses (square/rectangular waves) whose frequency and/or ratio between on and off is varied. As I hope we all have learned (by studying electronics and/or math) any fast transition between on and off produces an infinite series of harmonics, the strength of which depends primarily on the speed of the transition. ``` ```Switching power on and off is a fast transition -- we often hear it in our radios as a short pulse (even a crackle) of noise. That variable speed waveform is doing it thousands of times a second, produces a continuous train of crackles. ``` 73, Jim K9YC On 5/11/2018 12:36 PM, Dale Johnson wrote: ``````Question, what is considered a variable speed motor or furnace blower/fan? I have a furnace that has variable speeds, one higher speed for when the air conditioner is on then there is a couple speeds for when the furnace is on, one lower, one higher when demand is greater, is this considered a variable speed blower or fan? The furnace that I have produces no RFI that I can detect. `````` _______________________________________________ RFI mailing list RFI@contesting.com http://lists.contesting.com/mailman/listinfo/rfi ```
 Current Thread [RFI] AC American Standard, k5hab@arrl.net Re: [RFI] AC American Standard, Dale Johnson [RFI] What Does Variable Speed Mean?, Jim Brown <= Re: [RFI] What Does Variable Speed Mean?, Dale Johnson Re: [RFI] What Does Variable Speed Mean?, GARY HUBER Re: [RFI] What Does Variable Speed Mean?, Howard Lester Re: [RFI] What Does Variable Speed Mean?, GARY HUBER Re: [RFI] What Does Variable Speed Mean?, Dale Johnson Re: [RFI] What Does Variable Speed Mean?, GARY HUBER Re: [RFI] What Does Variable Speed Mean?, Dale Johnson Re: [RFI] What Does Variable Speed Mean?, Dale Johnson