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

"krj" wrote in message
...
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

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.

Sail magazine, June 2005.

Gordon West recommended:

1. Wrap compressor and controller in copper foil and ground the foil to
the compressor's metal mounting legs;
2. Install ferrite chokes on the control wires coming out of the
controller, as close as possible to the plastic controller box; and
3. Wrap controller box with copper screen from a hardware store.

Cheers

wrote:
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.

Sail magazine, June 2005.

Oops! It was the July issue, 2005, not June.

Cheers

Bil

wrote:
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.

Sail magazine, June 2005.

Gordon West recommended:

1. Wrap compressor and controller in copper foil and ground the foil to
the compressor's metal mounting legs;
2. Install ferrite chokes on the control wires coming out of the
controller, as close as possible to the plastic controller box; and
3. Wrap controller box with copper screen from a hardware store.

Cheers

Thanks for the info. I guess I'll go get some copper screen and try it.
krj

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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This has been discussed on Rparts forum a couple of times. The power unit
of the BD series of compressors is a variable frequency inverter and is
notorious for creating RF noise. Danfoss makes an aluminum shielded model
but they are hard to find and don't help with conducted noise. The digital
thermostat is not normally a source.

Some things that will help are ferrite chokes on all wires going to the
power unit to reduce conducted noise. You may have to experiment with the
size to cut the frequencies that you need. Also lining the compressor
locker with metal screening tied to ground reduces radiated noise.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"krj" wrote in message
...
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

krj wrote in news:A%Ihh.1397$cB6.766
@bignews7.bellsouth.net:

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

That "morse code" sound is a NEMA sentence bleeding into 12V wiring
through an improper connection. Check out this excellend site for info.
on how to check and correct.
http://www.shipmodul.com/en/connections.html

That "morse code" sound is a NMEA sentence bleeding into 12V wiring
through an improper connection. Check out this excellend site for info.

on how to check and correct.
http://www.shipmodul.com/en/connections.html