Danfoss make an enormous number of compressors. They are everywhere in cooling machinery. They are especially prevalent in boats where they are by far the most common refrigerator compressor.
What the heck? So why is that of interest the average ham radio operator. Well the answer is simple, they’re also very well known as a significant source of QRM.
So why does that matter to me? I’m operating for part of my stay in the Bahamas at stocking island which forms the north east coast of Elizabeth Harbour. As the winter progresses, more and more boats arrive to pass a few weeks in the sun. These are cruising yachts and most have refrigerators. The west coast of Stocking island is where I have been operating and the bay with the dock seems to attract the boats.
This has been very convenient until recently but as more and more boats arrive the steady ‘chirp’ of the Danfoss compressor has become more and more problematic. When they all get going its a bit like a summers evening in the Mediterranean with cicadas. Although they are more noticeable on the lower bands, the QRM extends as far as 17m where it will change a quite workable QSO into a nightmare. Worse still, the fridges are thermostatically controlled so you might think you have found a quiet frequency only to get nicely settled into a pileup when Mr Danfoss decides it’s time to spoil your fun. I hope this explains why sometimes I give a 5/7 (just above the noise floor most of the time recently) and then sometimes struggle to work the station. It was particularly bad today working Europe and eventually I had to give up. So as more and more boats arrive, I am considering, in the interests of productivity, moving my QTH a little further away.
I have a new QTH scoped out but this one does not have a dock although the takeoff for Europe is slightly more favourable. Another downside is that there is no convenient tree within reach of the length of coax I have with me. That is somewhat offset by the fact that is on the local nudist beach so there may be some compensations. No – don’t ask I am not doing SSTV!