Tim (& others) —
Be very careful when comparing a single 8-conductor rotator cable with two 4-conductor cables.
Typically, 8-conductor rotator cable is special in that two of the conductors are heavier gauge
(larger conductor diameter) for use with the Ham-M and TailTwister rotators. This is true of the
DXEngineering 8-conductor control cable that costs $0.89/foot. I think you’ll find that
it’s NOT the motor but, instead, the brake wedge SOLENOID inside the Ham-M and TailTwister
rotators that draws a lot of current and dictates the use of heavier gauge wire for two of the
wires. In contrast, the motor leads in those rotator models are normally assigned to two of the the
remaining six wires, which are smaller diameter. I don’t know about the newer (MFJ) manuals
for the TailTwister, but Cornell-Dubileer (aka CDE, the original manufacturer of those two rotators)
used to include enough information on the maximum allowable build-up of resistance in the various
leads that you could figure out the wire gauges you needed once you knew the total distance of your
rotator cable run from the base of the rotator to the back of the control box.
I couldn’t quickly find a 4-conductor control cable selling for $0.29/foot on the
DXEngineering web site, but often all the wires in a 4-conductor cable will have the same diameter,
so it’s not unreasonable to expect two 4-conductor cables to be less expensive than a single
8-conductor ROTATOR cable. It’s generally not an apples-to-apples comparison.
Also, if the rotator you’re using doesn’t have a brake wedge or other high current component
atop the tower, you may not need special “rotator cable” at all.
One trick for Ham-M and TailTwister rotator owners is this: Two of the wires in the
8-wire cable are solely for connecting an AC electrolytic capacitor (located in the
control box) across the motor windings. If you obtain a separate electrolytic and
mount it at the rotator housing, you can eliminate two of the eight wires running back
to the control box in your house! I’m not familiar with the current state of
the art in electrolytic design, but electrolytics always used to be notorious for
having very sloppy temperature coefficients of capacitance at low temperatures so the
higher your Latitude the more you may have to fuss in winter with the exact value of
an AC electrolytic that is mounted outdoors.
And there’s no reason you can’t locate the capacitor is at the base of your
tower and just run some simple zip cord up one leg to the rotator.
Depending on the length of the run to your rotator, you may find that jacketed standard 14-ga. branch circuit house wiring cable is
perfectly adequate for your high current leads, and in conjunction with some “ordinary” (i.e., smaller diameter
conductors) 4- or 6-conductor cable may even be less expensive than buying so-called “rotator” cable. However, one
advantage — if the price is OK — to 8-conductor “rotator cable” is that the overall diameter of the cable
is smaller than the effective diameter of marrying some dissimilar cables as I describe above, so it tends to be visually quite
unobtrusive. Some brands have a battleship gray jacket, which helps even more.
Bud, W2RU
On May 10, 2016, at 12:15 59PM, john@kk9a.com wrote:
It has been decades since I bought actual rotator cable. Typically the
motor requires a larger conductor than the sensing wires so I would
imagine that actual eight wire rotator cable would have two larger gauge
wires and six smaller ones.
John KK9A
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