We can add the new Chamberlain "PD" series garage door openers to the
growing list of RFI-generating devices. Two weeks ago, I replaced a
Chamberlain HD series model but found that this series is long out of
production.
In the case of my PD series opener, it was generating RFI on 80m. It caused
a 10 dB rise of the noise floor and also generated 40 kHz switching "bumps,"
the type of which we've all become familiar. Investigating the
transmission mode a bit further, I found that the switching supply is
coupling RFI onto the lines leading to the wall switch as well as the lines
leading to the optical safety sensors.
To cure the defect, I added several feet of control wire on each line at the
opener. This allowed me to wrap 10-tuns of the bundle onto a large #31
ferrite core. That reduced the RFI level but did not eliminate it. The
opener is about 30 feet distant from my balanced open wire feeders. I had
several 0.1 uF Sprague Orange Drop caps and installed them on each of the
four wire leads, each bypassed to chassis ground. That solved the problem.
Whether or not this is a problem in other installations, the magnitude of
the RFI detected will be affected by the proximity of the opener wiring to
antennas and transmission lines, especially open feeders. In addition to
this problem, the new openers are not backward compatible with an older
vehicle's HomeLink opener (typically located near a sun visor or rear view
mirror). My daughter's 2011 SUV and XYL's Mercedes will not open the new PD
opener. For that, Chamberlain sells a HomeLink "repeater" to bridge the two
technologies. Unless there's a compelling reason why the new openers could
not be designed with backward HomeLink compatibility, the design error is
unforgivable.
Paul, W9AC
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