On the topic of tuning an antenna by folding back the wire on
itself, rather than cutting:
Quoth KG0KP...
Seems to me -
This "folded back" discussion needs to specify BARE wire wrapped. If you
are not using bare wire and wrap the folded back section, things will change
(I suspect the change would be less if you electrically connect the end of
the folded back section back to the antenna but this will be a pain when
trying to tune).
-0-
Seems to ME, that if you're using insulated wire...which I do exclusively...
that you don't WANT to strip it. Just fold it back and see what happens.
Dielectric effects will be included in the resulting vswr curve.
When you reach the point you want, you can either a) leave it alone, or,
b) cut and finish the ends. I favor a.
My process for an inverted Ell is pretty much like for dipoles. Make 'em a
bit long, and fold 'em back til you land where you want.
My 80/160 dualband vertical used 4 elevated radials for each band, and open
wire line for the lower 65'. It was calculated for 1830. Radials were about
15' high at the feedpoint, and lower at the ends. For 160, I just folded
back
the radials equally until the vswr center was where I wanted it.
80 required pruning of the 450 ohm OWL, to get it up to 3600. About 62.5'
was
right. THEN, I could foldback the radials to move it up-band, if I needed.
Since I had to cut the 80m radiator, rather than folding it back, I went in
progressively smaller steps. 1', 0.5',0.5', 0.25', 0.25', etc.
Elevated radials start out at 105% of 234/f, while the radiators are at
234/f.
In the case of dipoles, I use 234/f. For Inverted Vees, 105% of that.
Been doing it that way since I was a nipper. Cut my first dipole to
textbook
specs and found it too short. Been cutting 'em long and folding 'em back
ever since.
N2EA
ps: a measuring hint to save time... carefully measure the fingertip to
fingertip distance
of your outstretched arms. In my case, 5.5' is the tip to tip
distance....and I've measured
all my antennas using that method. Once, when challenged, I pulled out my
long tape,
to verify, and found I had a 3" error in a 160m dipole. Fingertip to nose
can be another
useful distance. 'course, if your measurement is 5' 2.375", the math is a
bit gnarlier.
But I've always found that environmental variables more than swamp out the
measurement
errors.
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