amateur radio - Hackaday

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Capstan Winch Central to This All-Band Adjustable Dipole Antenna

Posted: 23 Feb 2021 07:00 PM PST
https://hackaday.com/2021/02/23/caps...ipole-antenna/


The perfect antenna is the holy grail of amateur radio. But antenna tuning
is a game of inches, and since the optimum length of an antenna depends on
the frequency its used on, the mere act of spinning the dial means that
every antenna design is a compromise. Or perhaps not, if you build this
infinitely adjustable capstan-winch dipole antenna.

Dipoles are generally built to resonate around the center frequency of one
band, and with allocations ranging almost from DC to daylight, hams often
end up with a forest of dipoles. [AD0MZ]s adjustable dipole solves that
problem, making the antenna usable from the 80-meter band down to 10
meters. To accomplish this feat it uses something familiar to any sailor: a
capstan winch.

The feedpoint of the antenna contains a pair of 3D-printed drums, each
wound with a loop of tinned 18-gauge antenna wire attached to some Dacron
cord. These make up the adjustable-length elements of the antenna, which
are strung through pulleys suspended in trees about 40 meters apart. Inside
the feedpoint enclosure are brushes from an electric drill to connect the
elements to a 1:1 balun and a stepper motor to run the winch. As the wire
pays out of one spool, the Dacron cord is taken up by the other; the same
thing happens on the other side of the antenna, resulting in a balanced
configuration.

We think this is a really clever design that should make many a ham happy
across the bands. We even see how this could be adapted to other antenna
configurations, like the end-fed halfwave we recently featured in our $50
Ham series.