More recently, I moved on to a very robust, all-aluminium version. Whilst this worked well, it is somewhat too heavy and, especially, the 2.5m-long top load catches more wind than is ideal.
My latest idea was to make this antenna more portable-friendly, based once more around the first seven sections of a 10m fibreglass fishing pole, but with physically smaller end loads. With the seventh section being about 25mm in diameter, the pole is quite stiff, and quite resistant to strong winds.
A quick forum post on QRZ.com brought an unusually constructive response from one fellow operator, who suggested the rather obvious solution of disc-shaped end loads. I thought I would have a go at this.
My first test end loads were about 30cm in diameter, which were calculated from guidance in the ARRL Antenna Book. This very nearly worked out, but not quite. My TS480SAT's internal ATU could only match the antenna down to 14.260MHz, so the loads were slightly too small.
I decided to build loads 40cm in diameter, a nearly doubling of total area, which connect to two vertical wires, each 2.5m long (essentially, a 10m vertical dipole, plus end-loads). To maintain self-support, I used 1.8mm bare copper wire, which proved to be a good choice. So that the hat will fit over a fence post that holds my fishing pole, the hat is made as a concentric set of rings.
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| Careful soldering is needed to ensure mechanically-robust links. |
Autumn conditions have now swept in from the Atlantic after two months of very dry, hot weather. So it wasn't the best day to test the antenna, as winds exceeded 100km/h under very enormous cumulonimbus clouds.
Having hooked everything up with the 300Ohm twin, I found the antenna now matched up easily right down to the lower end of 14MHz. I could match all bands except 28MHz, but could overcome that simply by detaching the lower end load. This might seem to make the antenna very unbalanced, but because one end of the dipole is much closer to the ground than the other, it is already unbalanced and removing the hat for 28MHz probably makes the antenna relatively balanced, overall.
I have to admit that the weather was quite dangerously close to generating lightning locally, with plenty of storms already underway across the UK. Interestingly, and very unusually, propagation was extremely variable on all bands. One minute they were strong, then all of them would fade together, as though a geomagnetic storm was happening (geomagnetic conditions were fairly quiet). I suspect this was related to the strongly convective weather, and indeed, the MST radar in Aberystwyth shows very strong returns, probably the result of strong gravity waves, the structure of which is, unusually, actually evident, induced by severe thunderstorms.
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| Very strong returns from the mesosphere today. |
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| Not a good day for operating! |
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| The top hat proved unperturbed by very strong winds. |
I ran a quick WSPR test. Overall, and although the power output for my field set up was not calibrated, the end loaded dipole was about 2dB weaker on the median than my vertical delta loop across all distances, and about 4dB weaker on DX distances greater than 6000km.
Because the delta loop is effectively a pair of closely-spaced verticals, that difference is pretty much exactly what one would expect, compared to a single vertical dipole. So the end loads are not having a noticeably negative effect on efficiency. The radiation pattern seems to be a little higher for the dipole.
I found the antenna could withstand winds of 100km/h and more without guying, but a single guy to windward certainly made things less exciting! In those conditions, taping or clamping the sections was essential to avoid slipping. This is now an ideal multiband antenna format, just 6m total height, for portable working.
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| Later WSPR test over about 1 hour at 14MHz. MW1CFN/P is the end-loaded vertical. |
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