[TowerTalk] "K" factor gets sillier

[Pete Smith]

At 01:28 PM 7/21/00 -0700, Stan Griffiths wrote:
>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.

Yes, but that's what's silly -- a lightweight 40m monobander like a Force
12, mounted on a heavy chrome-moly mast, would have a much higher K factor
than a heavier antenna of like size on a lightweight mast.  In the real
world, the weight of the antenna is being multiplied by the lever arm(s)
through which it acts on the rotator, while the mast contributes very
little to the inertia the rotator must overcome.
>
>> 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 . . .  ? ?

Stan, I think you misunderstood me -- I said not to exceed 60 percent OF
the K factor, rather than not to exceed the K factor by more than 60
percent...
>
>> 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.

Yes, but as I mentioned above, the lever arm through which this weight
operates is trivial compared to the rotating radius of the antenna, yet
they want you to count it as if it was all at the farthest point of the
antenna, which gives it a very inflated role in the antenna's mass picture,
and further cuts down on the amount of antenna you can turn with a given
rotator without exceeding their spec.

To give an example, if your mast plus antenna weighs 88 lb and the turning
radius of your antenna is 6 meters, Yaesu says the K factor is 240, and you
need the G-2800, for almost $1000.  Yet that's the description of a Force
12 C-3 on my current 10-foot mast.  According to Yaesu's previous
definition of the K-factor, that 32 lb antenna could easily be turned by a
G-800 at $319.

So basically, I stand by my point.   


73, Pete Smith N4ZR

The World Contest Station Database 
is back up and running at
http://www.qsl.net/n4zr 



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