[TowerTalk] Rotator Control Cable

[W2RU - Bud Hippisley]

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 at 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
>