[TowerTalk] "K" factor gets sillier

[Leonard Kay]

It sounds like Pete is saying:

1) Yaesu is recommending that you not exceed **60% OF** the K factor -
NOT that you not exceed it BY 60% (let's hope not!).  I.e. if the
K-factor is 1000, then don't go above 600 (not 1600). But then the
question is still valid... why not derate them all by 40% and just
say that you can't exceed them?!?

2) More importantly, I interpreted what was said to mean that
Yaesu wants you to multiply the mast weight by the ANTENNA's
turning radius - that sounds completely wrong. If you're going
to include the (probably negligible) effect of the mast weight
times its OWN 1"-2" turning radius, that seems to me to be the right
way to do it.  Maybe that's what Yaesu meant?!? But then, even a
100 lb, 2.5" OD mast would only give a K of about 10 ft-lbs.

Len K1NU

-----Original Message-----
From: Stan or Patricia Griffiths <w7ni@teleport.com>
To: Pete Smith <n4zr@contesting.com>; towertalk@contesting.com
<towertalk@contesting.com>
Date: Saturday, July 22, 2000 3:57 PM
Subject: Re: [TowerTalk] "K" factor gets sillier


>
>Hi Pete,
>
>My comments are interspersed below:
>
>Pete Smith wrote:
>
>> Imagine my amusement to discover that Yaesu now defines the K factor to
>> mean the product of the antenna weight and turning radius, PLUS the
weight
>> of the mast (or a share of the mast in the case of multiple antennas)
times
>> the turning radius!
>
>My understanding of "K Factor" is that it is supposed to be a measure of a
>rotator's ability to handle starting and braking torque loads as well as
>rotator torque loads due to wind gusts.  So, if you are going to compare a
>rotator's K factor to your antenna configuration, you need to consider
every
>bit of mass that the rotator is expect to turn and/or stop by braking.
Whether
>or not it is appropriate to include the mast can be answered by answering
the
>following question:  "Is the mast being rotated and/or braked by the
rotator?"
>Well . . . obviously YES it is, so it should be included.  If it is a long
>mast, the mass is significant, but the radius will always be small compared
to
>the antennas themselves.  Whether the product of mast mass times radius is
>large enough to impact the comparison of your antenna system to the K
factor of
>the rotator is open for discussion, ie: it depends on HOW large it actually
is.
>
>> Then just to gild the lily, they recommend that you not exceed 60 percent
>> of the allowable K factor for a given rotator,
>
>I don't really understand why it is acceptable to exceed the K factor at
all.
>I would think that a good definition of K factor would mean that you don't
>exceed it, at all, ever.  If exceeding it by 60% is OK, why don't we just
make
>all K factors 60% larger in the first place . . .  ? ?
>
>> and they caution that even
>> if you use a thrust bearing, you still have to count the mast weight in
>> your calculation!
>
>For this concept, you have to go back the the original question:  "Is the
mast
>being rotated and/or braked by the rotator?"  Well . . . yes, it is.
Having a
>thrust bearing in place does not affect the fact that the mast is still
being
>rotated and braked by the rotator.  Therefore, its mass and radius must
still
>be considered when comparing your antenna system for K factor compatibility
>with a rotator.
>
>> This K factor thing gets further and further from physical reality, and
>> looks more and more like CYA/marketing of bigger rotators!
>
>Other than the 60% fudge factor, it seems a little more "real" to me if the
>mast is included in the calculations.  I would think if the manufacturer's
>intent was to get you to buy a bigger rotator, they would never suggest you
>could exceed the K factor by any amount, let alone 60%.
>
>>
>> 73, Pete Smith N4ZR
>
>Stan  w7ni@teleport.com
>
>
>
>
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