[TowerTalk] Booms

[Mel Whitten]

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 at contesting.com] On Behalf Of Tom
Hellem
Sent: Saturday, March 11, 2017 7:23 AM
To: towertalk at 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 at 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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