Maybe you ought to check out "FTA" reciever on the web..several
sites...but be carefull there are some scam sites out there...


Graywolf wrote:
George,
wrote in message
news

Thanks for the info. I had originally thought there was a DC and
it
was reversed by polarity. This is a more unusual setup, at least
from
what I am familiar with. I find it hard to figure out how that
capacitor causes the reversal, but as long as it works. If I am
correct, this tells me that one wire is forward, on reverse and one
common (ground). That leaves the 4th. Let me guess, that one
controls the indicator position, and I would guess thru some sort
of
resistance variation ???? The rest and what you explained makes
sense.

The capacitor, in series with one winding changes the AC phase
of the applied winding voltage. Remember I said it was a two-
phase motor.

The indicator function is not always that simple. Alliance
made one rotor where the control box had its own synchronous
motor that turned the same speed as the rotor. You turned the
knob to the desired azimuth which closed the internal switch.
The switch was opened when the position of the motor in the
control box matched the azimuth setting. However, occasionally
the two motors would get out of sync with each other. Turning
the knob to first one end of its range, letting the internal
motor stop, and then turning the knob to the other end of its
range and waiting for the internal motor to stop would
synchronize the two. This worked by having one of the two
motors reach its mechanical stop while the other still turned.

Another version used a rheostat winding in the rotor unit that
supplied a meter in the control box. This is a special AC
meter and one which is not easy to duplicate. Yet another
version used a switch inside the rotor that was attached to a
gear such that the switch was momentarily closed every few
degrees. In the control box, there was a solenoid that pulled
a ratchet that drove the indicator mechanism. The indictor
jumped in rather coarse steps and clicked loudly.

Probably the most modern system Alliance made used a five-wire
cable. The rotor had a much higher resistance internal
potentiometer than the older models. It was fed from DC and
drove a null-balance circuit. The control box had a matching
potentiometer, and the motor direction and the starting and
stopping was controlled by whether the resistances matched each
other.

I recall trying to find some of those non-polarized caps for a
speaker
crossover setup. Not easy to find. I never know about using two
standard caps in that manner.

Non-polar electrolytics are two aluminum foil sheets coated
with the anodic oxide film wound together with a small moist
separator in between. Unlike conventional electrolytic
capacitors, they cannot be reformed and they do not heal.
Hooking two conventional electrolytics like I suggested forms
the same capacitor but it is physically larger.

Send me your email address and I will send you two articles on
electrolytic capacitors you might find useful. Take out the NO
SPAM in the address below to email me.

PS. How would I determine which is the common wire? I would assume
the other two don't matter, it either turns one way or the other.
The
4th, I am not sure how that one would be determined.

Get out the venerable old ohmmeter. The motor windings have a
moderate resistance, although I don't remember the value (and
very old Alliance units used much finer wire too). You should
find approximately the same resistance from one wire to two
other ones. This is the common connection. To verify, the
resistance between these two other wires should be double this
resistance. Between common and the indicator wire, you may
measure anything from a few ohms to an open circuit depending on
which model is installed.

Back in the 1960's, the ARRL did some tests on antenna rotors.
When installed with the external thrust bearing bracket, the
Alliance rotor was found to be almost as strong and far more
rugged than the much larger ham rotors. The article was in QST
sometime between 1965 and 1967.

73, Barry WA4VZQ