Sep 22, 2013

RFI problems

N 51° 35.564', E 3° 43.165'

Previously I wrote about our first installation of SSB radio with Winlink. After a great struggle we were happy that it was at least working somehow.

It wasn't that easy, as you might have guessed.

I was requesting a GRIB file while sailing and Simrad autopilot steering the boat. When the radio started transmitting, the boat started spinning. I was alone at night watch. It was good that nothing bad happened.

At the next marina we found out that RFI (Radio Frequency Interference) was making the rudder angle sensor to report ridiculous angles.

There are two ways the RFI can get to rudder angle sensor. Through air or through 12V electricity.

Wire to the sensor was long and the shield was not grounded. I changed the wire, added a ferrite bead and a 0.01?F capasitor parallel to sensor wires. It helped, but not enough. Angles were still changing about 10 degrees when transmitting.

Next I checked the 12V system. When not transmitting it looks like this:

Some of our battery chargers are making the nice figure.

When transmitting it looks this:

Icom IC801E is really causing trouble. It is taking about 30 Amps and it has bad decoupling.

Eliminating RFI is not easy. I added a ferrite bead to SSB power input.

After that the angle changes were only 1-2 degrees.

I also put 0.1?F capasitor parallel with 0.01?F capasitor connected to ground at both sides of this inductor, making it as a ?-filter.

Problem is now solved. No problems with autopilot. As long as we are transmitting higher than 7 MHz. We are not expecting to have good connections below 7 MHz at sea anyway.