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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