The system as quoted below is typical of most rotators.

73 de G3YXX

In message <[log in to unmask]>, David R. Basden
<[log in to unmask]> writes
>Two of the lines in the cable to the rotor connect to a pot in the rotor
>that changes resistance as the rotor turns.  This can be used to control
>the pitch of an audio oscilator.  The circuit for the oscillator was in QST
>over 20 years ago.  I don't believe I have the information any longer, but
>it should be available if you search for it.  Essentially the way it works
>is to rotate a rotary switch till the pointer is in the desired
>direction.  The rotary switch selects among various fixed resistors.  The
>pitch of an audio oscilator changes as you rotate the switch.  A push
>button switches between the pot in the rotor and the resistors on the
>rotary switch.  You just rotate the antenna until the pitches match.  I
>wish I could be of more help.
>
>73,
>
>Dave, A F 6 Y
>
>At 11:04 PM 6/9/03 -0400, you wrote:
>
>>I'd like to get a beam back up for HF.  My Ham IV has been packed away for 7
>>years since coming from the old QTH.  At that time I could still look at the
>>meter and see where it was pointed.   Can this thing be made accesible?
>>Perhaps via computer control?
>>
>>73 Steve KW3A
>>[log in to unmask]

--
David W Wood