A few weeks ago, I asked about Orion rotators, and the requirements
for fancy cabling. A new Orion owner told me that the factory
recommended two shielded #22 conductors for the pickup circuits, and
three heavier conductors for the motor.
I posted a question, soliciting experiences with these rotors.
* Several were using runs up to 500' without problems, using
standard multi-core cables. In some instances, Belden 8 core
rotator cable was being used, with pairs carrying the heavier
current (i.e. two cores for pickup, 2 x 3 cores for motor drive).
* One reported AC pickup problems while using an A/D converter to
read the position off a HyGain rotator (in a homebrew controller).
The solution was an active low pass filter.
* Several reported problems with moisture in the connector, which
caused major indicator problems. Apparently, even minor
condensation in the connector up on the tower would cause wildly
While I have not seen the manual for the OR2800P, I believe that the
positioning system actually uses a pulsing encoder with a counter
(rather than an analogue system). If that is true, the A/D converter
problem should not be relevant to the Orion. The moisture in the
connector could cause trouble, as a very high impedance circuit like
that would require very little leakage to get confused.
I just got off the phone to Mike Staal, one of the Ms of M-Squared
(and formerly the M in KLM) and the technical driving force behind
the company. He says:
The pickup problem is definitely only a problem on very long runs
(over 300'). The problem is with counting pulses (on the position
indicator) being coupled back into the counter circuit.
Solution: Use a single coaxial cable for the pickup. The cable
carries around 100 uA, so its conductor guage is not critical. The
mechanical manageability of having a surviveable cable in the duct
will probably dictate the dimensions. Suitable solutions include
RG58 and audio cable (the very thin stuff, around 1 mm diameter).
Chris R. Burger
PS: For those with traditional values, 1 mm = 13/331", or 27/686"
in round figures.
PPS: Yes, I know how the Ancient system works. You might even 5/128"
if that is more comfortable to you, or even 1/32" if that is close
PPPS: Yes, that is my idea of a joke.
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