Rain, rain, rain...

Thanks to an almost stationary, lawrge low pressure system over SE Iceland waters, it has been extraordinarily rainy over much of the UK the past few days.

When it rains very heavily like this, I always see a modest reduction in the resonant frequency of my 20m vertical delta loop.  Normally, this only sees a small increase in SWR - or so I thought.

When connected to my IC-746, the SWR indication during wet weather is considerably higher than indicated by my FT-450 - up to 1.5:1 at the upper band edge of 14MHz (the antenna is designed for the lower end).  But it is also quite high at the lower end, maybe around 1.35:1.  These are not in any way 'bad', and indeed, compared to some antennas, they are good SWR figures.  My SARK-110 analyser confirmed the IC-746's account of what was happening.

I had a good look, in pouring rain, at what was going on.  Excessive capacitive coupling to hedges and trees?  Unlikely, as even with lots of growth, the overall density of plants isn't much different from previous years.  Water bridging the feedpoint?  Not a problem with other antennas; I dried and greased it - no change.  Feedpoint not properly located at the 1/4wave-0.06 wave point?  Measured and found it slightly off, adjusted - only a 0.04 SWR change.

Then I remembered some distant advice from the early days: "twin feed can't pass through metal, go around sharp corners, or get wet".

I went to have another soaking, and found a modest length of twin feed sitting in standing water.  I pulled the whole line out of some weeds that had overgrown it over the years, and raised it off the ground, propped-up by bushes.

Any change?

Yep!  At 14.100MHz, the SWR is now 1.11:1.

So, whilst twin feed works fine in the wet, you antenna will be more consistent if you keep it off the ground, and out of puddles!