[TowerTalk] "K" factor gets sillier
wa4dou@juno.com
wa4dou@juno.com
Sat, 22 Jul 2000 14:00:56 -0400
Hi Pete and Gang,
Guess it gets to be quite expensive chasing those little db's. My C3SS
weighs 27 # and 4 ft. of schedule 40 aluminum mast weighs 3.6 #.30.6 # X
turning radius of 13.5= 413. Guess i lucked out. Kurts response to this
subject makes a lot of sense to me. 73 Roy WA4DOU
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On Sat, 22 Jul 2000 20:50:18 +0000 Pete Smith <n4zr@contesting.com>
writes:
>
> 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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