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 wish you luck with the shielding. I used to sail on an Endeavour 35
with an Adler-Barbour ice box cold plate that just tore up VHF Channel
16, of all channels, with a pulsing noise. I'm on an Amel Sharki 41
ketch and have installed an Icom M802/AT-140 and insulated backstay on
the main. On this boat the noise source is a Guest dual 10A battery
charger that makes broadband noise across the HF band very strong.
Luckily, it is off at sea.
To shield that fridge unit, you'd need screen box (It doesn't have to be
copper. Aluminum will work fine.) with proper feedthrough capacitors for
each individual wires where it feeds through the box. The ferrite
absorbers, while useful, will not stop the radiation that must be bled
off INSIDE the box, to the box itself. This, in effect, creates a
"screen room" we had in every calibration laboratory I ever worked in.
In the lab, we had to protect the measurements from RF sources outside
the screen room. The 5KW AM radio station just outside Charleston Naval
Shipyard had no signal, at all, inside the room with the door closed.
This is what you are trying to create. Feed through capacitors are a
straight wire through the center of a low impedance capacitor from that
wire to the outside case of it that is threaded to connect it to the
screen box. The signal coming out the wire couples harmlessly through
the capacitor to the INSIDE of the box. The AC and control signals are
much lower in frequency so very little of them couples through to the
screen and they escape the box. An additional ferrite absorber will
attenuate anything that escapes further.
Best of luck to you. You'll find more noise sources as time goes along.
Anything in that boat that has any kind of switching creates it. Your
NMEA data network to the instruments is also a prime source of HF noise
because the manufacturers go on-the-cheap and use unbalanced outputs,
grounding one side of what should be + and - phased signal lines that
were supposed to balanced out its radiation. Now with even 1 ground on -
NMEA data lines, it radiates like hell the whole time the NMEA stuff is
running. Add that to the wires wrapped around screws and all unshielded,
again on-the-cheap, and it makes it much worse. You'll find NMEA's
signal all across the HF bands at regular intervals.
Larry
