[TowerTalk] Driv Elem Tuning

[Kenneth D. Grimm]

Ron Chambers wrote:
> 
> The practical side of assembling, building, erecting and tuning beams
> that are mounted on non-crank-up/down towers presents a problem. You get
> the thing all assembled per the design/manual, take it all the way to
> 60, 70, 80, or even 180ft with the help of several local OM's, put it on
> the analyzer and voila', the "tuning" is off a little. You could beg all
> your help to stay, go thru the procedure of getting it back down the
> tower and adjusting, then back up, etc....maybe just to do it  all over
> again....ad infinitum (maybe I could be a lawyer)......
> 
> So my question is, what are the REASONABLE limits, say, if you have a 3
> element beam (monobander? tribander?), of adjusting only the driven
> element length (which you can usually get to on top of the tower)and not
> diminish the ability of the antenna to achieve what it's supposed to?
> ...The point being that you are not going to touch the length of the
> reflector or director....(Yes, this was questioned after K5MR repaired
> his full-size 3 element 40M at 170ft and it was 'off' a little, we did
> NOT want to take that thing down...)

What a great question!  I hope someone who is into modeling will take
the time to come up with an answer.  Obviously, the correct thing to do
is to change all elements, but what is the magnitude of the penalty that
you pay for just tuning the driven element?  

I too, have been caught with a very large antenna erected according to
the manufacturers dimensions and which was a "little" off and wondered
if I really had to take the whole thing down or whether I could "get by"
with simply adjusting the driven element by a wee bit.  

For example let's take a 20 mx beam ...the ubiquitous HyGain 204BA.  You
put the thing together using HyGain's measurements for the Phone
settings and on top of the tower is resonates in the middle of the CW
band.  What happens to the pattern, gain, f/b etc. if you shorten the
driven element by 3 inches and leave the other element lengths the
same?  

73,
-- 
Ken K4XL
grimm@lynchburg.net
BoatAnchor Manual Archive - ftp://bama.sbc.edu

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