Richard Thorne wrote:
>Jim Lux wrote:
>> I've been looking at ideas for electrically raising and lowering a
>> vertical antenna (like a 6BTV or R7000 style... basically 20-30 ft of
>> aluminum tubing).
>> The overall idea is to hide a vertical antenna on a rooftop by laying
>> it down when not in use.
>I had the same question some time back. The best suggestion I received
>was using an elevation rotor. I never installed the vertical but if I
>did I liked this idea. I probably would have used some sort of counter
>weight so the system was balanced.
>The other way is to use a satellite dish actuator. While on a smaller
>scale Tarheel mobile antennas uses this idea.
From experience with moonbounce systems, a TVRO jackscrew would
definitely be the way to go. Elevation rotators that are based on small
TV rotators have a very poor reputation with anything larger than a
satellite array, because the small final gear gives a lever arm of only
a few inches.
By using a much longer lever arm of about 16in, a jackscrew with a 24in
travel can provide 90deg of rotation with a very large lifting torque at
the pivot point - far larger than you need for this application.
The lever arrangement should be designed to raise the antenna by pulling
on the lever, not by pushing, because compression tends to buckle the
long screwed rod. Also there should be an arm braced at 90deg to the
antenna, which rotates downward onto the roof as the antenna is raised,
and helps handle the compressive wind forces once the antenna is
vertical. Adjustable limit switches are already provided, of course.
When the antenna is lowered, the lever arm and jackscrew would need to
stand maybe 2ft above a flat roof, but that wouldn't be very noticeable
from ground level. If the antenna could be mounted at the edge of the
roof, the jackscrew could be pivoted from the wall below.
73 from Ian GM3SEK
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