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.
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?
Kim N5OP
On 2/9/2020 7:09 AM, Paul Christensen wrote:
"I put a pair of small pie wound chokes in series with the + and return
lines at the box's keying jack and that fixed the problem."
That often works fine on control circuits but for audio circuits and other
circuits that require maintaining signal waveform integrity, I now use
common-mode chokes and abandoned differential-mode filtering that uses
Pi-section L and bypass C components. For example, pass a square wave, or
any other fast, complex waveform through a Pi-section choke and observe the
result. Even when properly terminated, large overshoot spikes and ringing
results.
By contrast, a CM choke does not affect differential mode signaling as
there's no differential series L due to inductance cancellation. A CM choke
yields 2*L on common-mode currents, or twice the inductance of a single
winding.
We also need to be mindful of series resistance when using simple series
chokes in power supplies and high-power audio output circuits. We can
mostly ignore that with CM chokes except for the added wiring resistance
required with each turn through a core.
Paul, W9AC
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--
Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP
SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)
/"A great second violinist plays second fiddle to no one." //– Robert C.
Marsh, Chicago Sun-Times./
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