Dan Kovatch wrote:
All currently manufactured dimmers should have filters in them. I also found
> that if they(the noisy dimmers) were OFF or FULL on the noise went away.
> This may just have been my particular setup.
> --
Dan:
Yes, they should all have filters, but the bargain units usually do not.
Your observation about no noise if OFF or FULL ON is correct, for the
following reason. These dimmers work by cutting off conduction during a
portion of the sinusoidal cycle around the zero crossings. The resultant
chopped current waveform has a lower RMS value than the full sinusoidal
waveform, so the light is dimmer. The width of the nonconducting region is
set by the dimmer control. Unfortunately, the triac devices used can and do
oscillate at RF in the cutoff region, generating short bursts around the
zero crossings. The result is two RF bursts per AC cycle, or 120 per second.
This is the source of the characteristic 120 Hz (and harmonics) buzz in your
RX. The oscillation usually rolls off in the low MHz range, and typically
you will hear it on the AM BC band, 160, and maybe 80, but it is less likely
to be noticed at 40m or above.
Of course, if there is no current flow, or full unchopped current, such
noise is unlikely.
73,
Garry, NI6T
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