Snow and SWR

This morning, something very rare indeed happened on Anglesey, although it is hardly unusual in many other places.

The situation is best summarised by a temperature (blue) plot from the nearby, RAF Valley airbase:

In just 50 minutes, the temperature dropped from an already falling 6 degrees Celsius to just under 2 degrees Celsius.  All this in a strong, Beaufort Force 10 wind (which can occur several days a week during winter here in NW Wales).

It also happened to be snowing again - something that only really happens during solar minimum in this coastal location.

When I switched on at 14MHz for some breakfast operating, I found my delta loop was reporting a 1.5:1 SWR.  Normally, it never climbs above about 1.2:1 at my preferred, digital frequencies, and only then during or immediately after extremely heavy rain.

I hoped it wasn't wind damage that would mean time spent in very unpleasant conditions outdoors, conducting repairs.  When I looked at the antenna, the rare combination of weather conditions had led to snow accumulating on the antenna wires, despite the wind, which had then started to melt during the warmer temperatures, only to freeze quickly as the temperature plummeted within just a few minutes.  The antenna was therefore covered in small drop-like icicles, something akin to those American ice storms we often see in the ham press.  The ground was also saturated with melting snow water. The antenna therefore experienced itself as being somewhat electrically longer than expected.

As the morning warmed up, the delta loop match returned to 1.2:1, still higher than normal due to the ground remaining saturated.

I've often heard many people say that their radio reception is 'quieter' during snowfall.  Perhaps the reason for that is that their antenna has become detuned by water in various phases to the point where it is no longer doing what it should be doing at that frequency.  It may also 'detune' those AC and other non-antenna wires that emit the noise, so that it occurs slightly further down the bands.