My thanks to whoever posted the note on K-Factor from Eham.net!
All you need to know for the rotator is how much torque it will handle,
Calculate the K factor for the antenna, The rotator torque needs to be
greater than the calculated K factor for the antenna(s).
73
Roger (K8RI)
On 5/4/2016 Wednesday 5:15 PM, Jerry Gardner wrote:
On Wed, May 4, 2016 at 6:20 AM, Chuck Dietz <w5prchuck@gmail.com> wrote:
This was on Eham.net:
In addition to windload and torque ratings, Yaesu also offers a
specification called "K-factor," which is derrived by multiplying the
turning radius of the antenna (in feet) by the weight of the antenna (in
pounds). Add the K-factor of each antenna on the mast together for your
total system K-factor. The resulting number (in foot-pounds) must be less
than the K-factor rating for the rotator.
For example, the Hygain TH-11DXS has a 12.5 square foot windload. The Yaesu
G-800DXA rotator will handle up to 21.5 square feet. But, when you multiply
the antenna's turning radius, which is 22 feet, by the weight of the
antenna, you get a K-factor of 1,936 foot-pounds. So, although the windload
rating of the rotator would seem to indicate that it will handle the
antenna, the K-factor of the antenna is greater than what the rotator will
handle (1,302 foot-pounds). If we look at the K-factor rating of the Yaesu
G-1000DXA, we see that it is 1,663 foot-pounds, so it's not even the
correct choice. At this point we would need to use a G-2800SDX, which will
handle a K-factor of up to 6,870 foot-pounds, which is obviously much
sturdier than what we really need.
Seems to me that K-factor is a better measure than just sqft of wind area.
The OB17-4 would have a
K-factor of (30 ft x 220 lbs) = 6600 foot-pounds. Although the G-2800SDX is
rated for 6870, that's only a
4% margin. I prefer to have at least a 15-20% margin.
I've searched for a list of K-factors for various commercial rotators, but
wasn't able to find anything. Anyone have such a list?
73,
Jerry
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73
Roger (K8RI)
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