Conference 7.286::home_work

As I understand it the garden variety rotators are fed with a lower ac
volatage via two circuits (3 wire with a common).  The rotator is a common
variety ac motor which runs at lower voltages.  Each winding provides
for one direction.  Usually a similar ac motor on the controller end rotates
at the same speed while providing drive voltage to the rotator box.  So
if you want to drive this thing with a make shift unit it will have to
provide ac at a lower volatage (I'd have to measure mine to see exactly
how much) and your only real problem is providing some sort of indicator
which provides you useful data as to where the antenna is pointing.  

Synchronizing the units generally involves simply running the control box
through complete revs in both directions.  When the rotator on the roof
reaches its full travel it just stalls while the control box reaches its
full travel in that directions.

    I would suggest taking the part of the rotor that you have (since
    you already took it down from the roof) and take it to someone who
    does antenna installations and see if they can identify the make
    and model for you.  You may be able to buy just the control box.
    
    When I moved into my house last year, the previous owner didn't
    leave the control box and I managed to get another one for about
    half of what a complete rotor would cost.  Mine was an Alliance
    U-100 model, I believe.
    
    -willie
    

    Whilst roaming about the house today, I ran across the control box
    for my Archer (Radio Shack) rotor.  
    
    Dutifully, I cranked it up and measured the voltage across all
    combinations of the three wires. When quiescent, 0 volts. When turning
    in either direction, I got 25 VAC between all combinations.  This makes
    no sense to me.  I plugged it into the system just to make sure that it
    worked and it was fine. 
    
    What can I say?  It's probably like TV itself, if you think about it
    too hard, it won't work. 
    
    -joet
    

    re .3, that does make sense.  Most rotators use 24-25 volts.  But
    the motor in the rotator is a capacitor start motor WITHOUT the
    capacitor.  The capacitor is in the control box and is switched
    to the correct leads to control rotation.  Reading the voltage
    with a meter (which ignores phase) will see no difference between
    any of the leads.  Looking at it with something more sophisticated
    (like a scope) will.

    Aha!
    
    I take it, then, that the author of .0 would be better off buying
    rather than building.
    
    -joet

    Building takes a 24v transformer, a single pole double pole (center
    off) switch, and a motor start capacitor.  If you don't need a readout
    for direction, that's all you need.  If you DO need a readout, all
    bets are off.  Every manufacturer has a different way of doing the
    readout.  Some just use pulses from a contact.  Some use a rheostat.
    Some use a much more complicated scheme.
    
    Using one manufacturers control box on another's rotor has the same
    problems.  You can almost always get it to turn.  You usually can't
    get the readout to work.

Thanks for the replies so far.

I am not willing to spend $60 for a new rotator.  If I can make my existing
rotator work by kludging something up, I'll do it.

Since the rotator has only 3 wires, I assume that position indication is by
running an indicator at the same speed, as indicated in a previous response.
The control is "open loop".

I have figured out a way to do display indication.  That's no problem.

Do I just go to Spag's (or ?) and buy a "motor start capcitor", or do I need
to know the capacitance?

I assume I apply 24v to both sides of the motor, and only hook the capacitor
across one side.  Is this correct?

    Build your own motor start cap.  Take two electrolytic caps (a.
    la. radio shack) having a value of 50 or 100 microfarads at 50 volts
    or more.  Connect them back to back (+ lead to + lead).  The two
    negative leads are what you hook up.
    
    I'm not sure I can draw it here.  Maybe words will work.  One of
    the rotor leads is a "common" lead.  The other two go to opposite
    ends of a motor winding.  Connect the motor start cap. across the
    two leads that aren't common.  Connect the switch wiper to the
    24VAC supply.  connect the common lead from the rotor to the other
    side of the 24VAC supply.  Connect the remaining two connections
    on the switch to the two rotor leads you have the motor start cap.
    hooked to.
    
    Most 3 wire rotors I've seen don't have an indicator at all.  You
    just "tune" for best picture!

    I have a 3-wire radio shack box that I don't use any more.  When
    I left my last apartment, I didn't feel like climbing up on the
    roof to get the rotator (slate roof) and the guys that moved in
    were a**holes about buying it from me ($15.00 is what I asked) so
    I took the box.
    
    You can have it if you want. 
    I work in the Mill and live in newton.  give me a ring
    
    
    -bill