[TowerTalk] Rotator Choice for Larger Yagi

[Roger (K8RI) on TT]

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 at 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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