[TowerTalk] Resistance of Rotor Control Wires (see also CAT5 thread)

Larry Loen lwloen at gmail.com
Thu Jul 26 14:44:01 PDT 2012


I am trying to understand control wire (DC) resistance losses.  This
would be for my rotor control wire for my M2 atop my
soon-to-be-erected 72 foot tower.

I figure my total run is going to be fairly long -- about 215 feet
(for a variety of reasons, a straight cable run is not in the cards --
I have to go around my septic field and a shed).  The specs for the M2
rotor http://www.arraysolutions.com/Products/m2rotators.htm . . .show
the minimum cable gauges are 2 at number 18 and 2 at number 22.  This
probably relates to the total amperage delivered and the planned
voltage drop the unit can stand.

Calculations given here:
http://www.stealth316.com/2-wire-resistance.htm  . . .are suggestive
that I would want more like number 12 gauge if I wanted to keep the
voltage loss to half a volt (apparently, the M2 design can stand a bit
more?).  There are a couple of other sources, including this one:
http://www.mogami.com/e/cad/wire-gauge.html   which, while it
dispenses with the "circular mills" part of the calculations (at least
overtly) seems to me to create a similar conclusion.

This suggests to me that I should be looking at some hefty cable
gauges if I want to be "really sure" of things working, but I get the
impression that this is probably overkill, given what M2 itself seems
to be recommending.  A 72 foot tower would have a minimum run (if one
wanted to keep the shack out of the fall zone) of about 150 feet for a
75 foot total tower exposure.  And, I know M2s are popular with
VHF/UHF hams, where a lot of towers are taller still.  I'm sure lots
of M2s have 200 plus foot runs.

Still, in line with my overengineering of the project, what I probably
would find ideal is some sort of four wire shielded cable at somewhere
between 12 and 16 gauge if I could find such a thing.  Or, would
unshielded with a couple of ferrite beads at nor near the rotor be
enough?  That would simplify things quiet a bit.

CAT cable looks suspiciously narrow gauge for my run, at least.


Larry Wo0Z


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