krj wrote:
I just finished installing an SSB on my boat. When I turn on my freezer
I get noise on the radio that sounds like morse code. The freezer has a
Danfoss BD50 compressor with a digital thermostat. Has anyone else had
this problem. I think I remember Gordon West writing about this problem
in one of the sailing mags. but can't remember which one or when.
krj
I'm not familiar with the Gordon West article, but the following may help.
Digital thermostats often use microcontrollers capable of generating RF
interference. That is more likely the problem than the compressor itself.
The interference can be transmitted to the SSB either by radiation, in
which case the SSB is picking it up via its antenna, or by conduction
through the 12 VDC wiring.
To test the former possibility, radiation, simply remove the coax
connector from the SSB and carefully short the center conductor on the
SSB to the grounded outer conductor. Use as short a wire as possible and
try not to touch it. There is no risk whatever to the SSB or to you. The
idea is that your body not serve as an "antenna". Next, listen for
freezer noise on the SSB. If it is gone or even reduced significantly,
then a good portion of the noise is being radiated. Short of providing
RF shielding of the freezer electronics (which may be quite a task) your
best option may be to contact the manufacturer. These units are often
constructed with explicit RFI reduction circuits/components, which could
be defective in your unit.
If the noise is not being radiated, then it is being conducted via the
12 volt wiring. Bypass capacitors at the 12 volt connections to the
freezer (right at the unit itself) may cure the problem. Chokes and RF
filters could also be added to the SSB 12 volt line, although they would
have to be able to handle the current drawn by the SSB during transmit:
20- 30 amps.
There is a lot of useful info on the web, but it is important to know
how the interference is reaching the SSB. Meanwhile, maybe someone will
remember the Gordon West article.
Good luck.
Chuck
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