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@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@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@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@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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> >
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> >
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