# [TowerTalk] dipole length adjustment

David Robbins K1TTT k1ttt at arrl.net
Sat Jan 20 08:35:07 EST 2007

```I prefer the 'close enough' adjustment method.  This works for any units and
any band.

The formula is just     length*change/frequency

As long as the units of 'change' (how much you want to move the resonance)
and frequency are the same it will give you how much to cut or add in
whatever units you use for length.  Note that length can be the current
length, the desired length, or just the guestimated length for the band.
And frequency can be the current frequency, the desired frequency, or just
the center of the band.  As long as you don't try to use it to retune a 30m
dipole to 40m or something like that it will be 'close enough'.

Don't believe me... consider this case, a 40m dipole that is resonant at
6900khz and you want it at 7100khz.  Change =200khz

Assume current length is 32'
32*200/7100=.9'  (10.8" or lets say 11")
but if you were a bit off and its really 33'
33+200/7100=.92'  (11.04".. close enough)
but what if you used 7000khz or even worse 6900khz
32*200/6900=.92'

oh, prefer meters... assume current length is 10m
10*200/7100=.28m
really 10.3m?
10.3*200/7100=.29m (does 1mm really matter??)
or you used 6900khz?
10*200/6900=.29m

so don't worry about all the spreadsheets, fancy formulas, and other
stuff... just cut it long, find that first resonance, and snip away.

Oh, and remember this... how close is 'close enough' is proportional to how
hard the adjustment is to make.  That is, the harder it is to make the
adjustment (climbing a roof, or tower is harder than snipping from the
ground) the wider the limit is on 'close enough'.  Remember "Too low an SWR
can kill you!".

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net

```

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