On Tue, 2 Mar 1999 09:01:07 -0600, Roger Cox wrote:
Glad to see you're still out there hiding in the weeds...
>It has really been interesting reading the discussion on the K-factor and
>Effective Moment on the reflector.
An interesting observation of mine is that although *writing down*
these discussions can be difficult, just about all the hams I know
understand these things intuitively to some fair degree.
There is also a fair amount of cynicism about published ratings, which
they see through, even though they may have hesitance or difficulty
expressing it in a written medium. (As my favorite and nastiest
English teacher used to say, everyone likes to talk and noone wants to
The manufacturers who consistently put out reliable and standardized
specs WILL SELL MORE STUFF. People buy from those whom they trust. I
don't know why the commercial establishment has such a problem
learning this lesson. Pete is right about what needs to be published.
Just don't think he will have much luck.
>While I agree that our EM and Yaesu's
>K-Factor are not perfect, they are much better than the older "square
>footage wind area". The EM rating was developed from what was commonly
>available from all antenna manufacturers - weight and turning radius. It
>would be nice to have a physical model of every Amateur antenna on the
>market so that we could compute the actual wind torque, but this seemed
>unlikely since we also manufactured and sold competitive antenna products.
>The weight of antenna corrolates nicely to the diameters of the antenna
>elements and boom, and the turning radius also corrolates to both long boom
>and long element length antennas, so this is a good approximation with what
>is available. We looked at the failure history of our rotators versus what
>antennas were placed on them. We also asked Craig at the Rotor Doctor
>(C.A.T.S.) for similar information. There were two parts that usually fail
>when a rotor is overloaded - the main ring gear and the brake wedge. The
>ring gear failure occurs when you try to turn large antennas in high winds.
>The brake wedge fails either when the brake is engaged during rotation or
>during extreme storm conditions. From this failure history we derived the
>EM numbers. At the same time, we also improved the ring gear and the brake
>wedge so that they were less likely to fail.
Guy L. Olinger
Apex, NC, USA
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