[TowerTalk] 80m vertical size calculation

[w5prchuck at gmail.com]

But you are only adjusting the smaller diameter tube and not the larger diameter. Afterward, the antenna will have a larger percentage of the large diameter than before. Therefore, it is a different antenna then. In order for the ratio to work, you would need to remove the same percentage of each diameter. 

Chuck W5PR

Sent from Mail for Windows 10

From: StellarCAT
Sent: Wednesday, September 13, 2017 2:23 PM
To: Chuck Dietz; Charles Morrison; V. Sciucka
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] 80m vertical size calculation

Chuck,

The reason why this will work is because you are FIRST determining what the 
formula is for that particular antenna in situ. So if it were say 22M tall 
and it resonated at 3.467 Mhz then the "formula" for THIS antenna turns out 
to be :


72.16' (22M)  *  3.467 = 250.2

So for THIS antenna - where it is - in situ, you can use 250.2/Fmhz.

So then adjusting it a small amount - and that is key here we're not talking 
about testing it at 3.467 Mhz and deciding to redo it for 7.1 Mhz using that 
value ... for testing for this (relatively speaking) small change to say 
3.55 or even 3.8, a difference of only 10%, the formula will get you pretty 
darn close. If it were a bigger change - if you had it at 3.45Mhz and wanted 
to go to 3.8Mhz I'd suggest you started out 'wrong' for lack of a better 
term - but even in this case you can use this method. Variables like - for 
example with that size change of 10% if you whack off 7' and that 7' is ALL 
of the top diameter of 1/2" and the next diameter jumps up to say 3/4" it 
might be off by a little bit. But based on his request - he's in the ball 
park to start off - this will work just fine. I used it for all of my 
antennas when modeling/range testing - M2 and Optibeam antennas to put them 
where I wanted the performance to be.

Gary
K9RX



-----Original Message----- 
From: Chuck Dietz
Sent: Wednesday, September 13, 2017 2:33 PM
To: Charles Morrison ; V. Sciucka
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] 80m vertical size calculation

Maybe I don't understand, but I would think that if you had a tower with an
aluminum tube "stinger" on top, this might not work because of the change
in percentage of the various diameters.

Chuck W5PR

On Wed, Sep 13, 2017 at 1:00 PM Charles Morrison <junkcmp at gmail.com> wrote:

> Not length to diameter, It is independent of diameter.
>
> It is a simple method to determine a difference of length as a ratio based
> on frequency.
>
>
> On Wed, Sep 13, 2017 at 11:41 AM, V. Sciucka <vytenis.sciucka at gmail.com>
> wrote:
>
> > Thanks Gary K9RX and Charlie N1RR, 2nd question is clear now.
> > Charlie also gave formula for length 246/f(mhz) =  element (feet) which 
> > I
> > assume includes length to diameter ratio or this ratio is not so much
> > important.
> >
> > --------------------
> > Vytenis
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