Altho not normally pictured with "elements on top of the boom",
UHF/microwave loop elements (like K1FO designs) are more robust in hail
storms and big bird landings with elements on the bottom. I did not
realize this until after I had the loops mounted on top of the booms and hit
by hailstones and hawks.
Mel, K0PFX
www.melwhitten.com
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Tom
Hellem
Sent: Saturday, March 11, 2017 7:23 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Booms
Not all beams use elements on top. F-12 had theirs hanging underneath.
N6BT ( F-12 creator) said in his book that yagi elements naturally "want to
be that way". Seems to make sense.
K0SN
On Fri, Mar 10, 2017 at 8:55 PM, jimlux <jimlux@earthlink.net> wrote:
> On 3/10/17 7:12 PM, Ed Karl wrote:
>
>> Hey Troops-
>>
>> I've been around for a while, always wondered about this. Looking at
>> the discussion of square vs round booms. How come the elements are on
>> top of the round book?
>> Seems like less inclination to rotate out of alignment if they were
>> already on the bottom ...
>>
>>
> Tradition?
> Elements are on top with round booms too, probably because of assembly
> processes If you're assembling it on sawhorses, it's easier to have
> the boom sitting there, and then bring the elements over and mount
> them one by one, on top of the boom. If they're on the bottom you have
> to thread them around the sawhorse legs, etc.
>
> And then once it's assembled, who wants to try and flip it over
> (although it's not that hard, it is unwieldy.
>
> I can't think of any *electrical* reason why you'd care. On some LPDAs,
> the elements alternate top and bottom (both across and along the boom)
> if the boom is the transmission line.
>
>
> (and we'll leave aside any theories about the fact that the north
> facing owl will tend to sit on the element rather than the boom,
> because it's higher, and if you put the elements on the bottom, you'll
> have a 90 degree pointing error...)
>
> On VHF/UHF arrays with CP antennas, a common error is to not have all
> the antennas oriented the same (there's this tendency to make it
> mirror symmetric, because it "looks" more balanced). I may overstate,
> I've seen this error once, but I've only seen an array being assembled a
few times.
> Generally by the time most people look at it, it's been fixed.
>
>
>
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