Topband: Short verticals

[Manyoaks]

With the recent postings on inferior antennas and whether they work, I
decided to try a simple set up for the CQWW SSB this weekend.  I took down
my normal antenna and erected a 30ft top loaded vertical and went barefoot!

I have a tree 105 ft from the house so I used that and the ridge of the
house to form a top loading wire and ran a vertical down from the centre
point to make a 'T'.  Modelling the system showed that the top section
needed to be longer - OK it really said the vertical section should be
taller! - so I end loaded each end of the top wire with a further 10ft
looped back on itself and spaced 4 inches.  This helped, but to get
resonance at 1840 KHz needed a coil - so I built one out of 8mm (approx 3/8
inch) copper plumbing tube.  It took 8 turns on a 9 inch former - the tube
bends easily at this radius.  Placed at the bottom of the vertical section
with the bottom of the coil grounded, I was able to match to 50 ohms by
tapping up the coil.  I put out 16 radials - 8 were 60 ft long, the rest
were shorter.  It tuned up OK and had a 2:1 bandwidth of about 40 KHz,
which was less than I expected considering the low radiation resistance and
the poor earth.

With 100w and this compromise system I worked 35 countries in 7 hours of
operating.  Best DX was XE1RCS.  In general I could work all of Europe but
did not always get through on the first call and regularly had to 'wait my
turn'.  The country score could easily have been more if I had worked more
hours e.g. I did not work GW, GM, GI, GJ, all of which are
wet-string-workable.

I was surprised at just how well a 30ft top loaded vertical over an
inadequate earth system can perform.  So if anyone is still in doubt - just
put something up and enjoy the band .......

73 de Chris  G3SVL



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