As I feared when I first raised the issue of "precip static," the Quad
vs. Yagi debate has started once again. I appreciate Toms posting on
the subject and agree with his assessment. When Clarence Moore
developed the quad it was to simply keep the corona from melting the
ends off his arrays in the high altitudes of the Andes. It worked. It
also worked on receive. Quads are simply quieter than yagis when it
comes to corona/precip static. Tom acknowledges that to be true.
What still interests me is how to get rid of the noise on yagis that you
don't have on quads! Tom's "Big Balls" solution has a certain perverse
appeal to it, but I'll bet that none of the Yagi manufacturers are going
to put copper toilet floats out on the ends of each element! I just
looked out the window at my Force 12 EF-240/420 and the idea adding
bulbous end caps on elements that are already pretty droopy would
present a problem that not even Viagra would be able to solve. The
added mass at the ends of the elements would present all kinds of torque
related problems, so while it might reduce the precip noise, it's
probably not a practical solution.
On the other hand, the addition of a "dummy" antenna (yagi, spikey
thing, vertical or whatever) above the yagis that are to be used as
receiving antennas is an intriguing possibility. So, I'm planning on
adding an aluminum extension to the top of the mast that will extend
above the yagis. One thing has me puzzled, however. Tom says that it
should be capped with a smooth rounded surface (toilet float?) and
others suggest the use of the spikey devices. I would appreciate
comments on how far above the yagis this extension would need to reach
to do it's thing and also whether the rounded end is more likely to
reduce precip noise than the spikey thing.
73,
Tom Rauch wrote:
>
To: <towertalk@contesting.com>
> > Date: Thu, 30 Apr 1998 10:54:55 -0700 (PDT)
>
> > I had a 4 element yagi at 120 feet and noted some rain static. I
> > changed it to a 4 element quad and the rain static went away. Of
> > course the QRN from a local power line was the same.
>
> That isn't surprising. The yagi has points with high gradients (the
> tips) sticking out into the air, while the quad likely has a long
> flat sides all pulled in close to the tower.
>
> I would expect the quad to have less corona, and the corona it does
> have would not be at the highest impedance part of the antenna where
> energy is coupled more efficiently.
>
> However, the yagi could be cured by adding a large BLUNT conductor
> vertically that removes voltage gradient between the lower yagi
> elements and surrounding air.
>
> None of this has anything to do with a closed DC loop or DC ground,
> however. You yagi could be cured by adding smooth round balls to the
> elements. (no viagra jokes please ;-))
>
> 73, Tom W8JI
> w8ji.tom@MCIONE.com
>
--
Ken K4XL
grimm@lynchburg.net
Boatanchor Manual Archive - ftp://198.28.36.115/pub
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