[TowerTalk] Sateliite Dish Acuator Arm

[Ian White, G3SEK]

Scott E. Olitsky wrote:
>
>I would be interested in getting information from anyone who is using an
>actuator arm from a Satellite Dish to elevate an antenna system.  I am
>trying to figure out how I can read out the length of the arm and where it
>is pointing
>
>Scott

Almost all moonbounce operators are using satellite screw-jacks, because
they are so much stronger and better value than sidewise conventional
rotators. 

The readout methods vary a lot, depending partly on the position
transmitter in the screw-jack (gear-driven pot or repeating reed
switch). Three examples are:

1. An old multi-channel RX including a  dish controller, with the
controller part pre-set to channels 0-90 (degrees). This obviously needs
a compatible position transmitter on the screw-jack.

2. With a pot readout, either a voltage or resistance meter with a
conversion chart. It's also possible to plane the geometry so that a
voltmeter readout is very nearly linear (reads low at both ends of
travel, high in the middle, but always closer than about 2 degrees).

3. An independent pot on the antenna, with a plumb-bob. This can give
accurate linear readout but is subject to wind effects and/or vibration. 

A Wheatstone bridge arrangement is a favorite for potentiometer readout,
because you can adjust the zero and span independently.

There are some ideas, pictures and links on the Moonbounce part of my
web site - in particular see G4ZHI's system.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           http://www.ifwtech.demon.co.uk/g3sek

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