Dipole Length Question
 

Robert Kole wrote:
I know it's nit-picking and the tuner will handle it,
I just want to know what's "correct".

Your 3 1/3 inches is only about 0.3% of the total length.
Whether the wire is insulated or not can make ten times
that amount of difference but you didn't tell us what kind
of wire you are using. Not only is it a nit, but it is a
negligible nit compared to other nits. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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In article , Cecil Moore wrote:

[snip]

Not only is it a nit, but it is a
negligible nit compared to other nits. :-)

O.K. I'll have to find something else to
obsess about. G

102' 3-1/2"... less than that and your feedline narrows down again,
defeating the purpose of building your own feedline exactly 3-1/2" wide...

73,
Mike KI6PR
El Rancho R.F., CA


"Robert Kole" wrote
I'm putting up a G5RV fed with homebrew ladder-line
spaced 3 1/2" apart. Should I include the 3 1/2"
in the overall length?

Put another way; shoud the overall length of the ant
be 102' or 102' 3 1/3" ?

I know it's nit-picking and the tuner will handle it,
I just want to know what's "correct".

(A thousand pardons if this has been asked over and over.)

On Thu, 22 Apr 2004 03:39:27 +0000 (UTC), Robert Kole
wrote:


I'm putting up a G5RV fed with homebrew ladder-line
spaced 3 1/2" apart. Should I include the 3 1/2"
in the overall length?

Put another way; shoud the overall length of the ant
be 102' or 102' 3 1/3" ?

I know it's nit-picking and the tuner will handle it,
I just want to know what's "correct".

(A thousand pardons if this has been asked over and over.)

See Cebik's G5RV article at

http://www.cebik.com/g5rv.html

for the length of the dipole. G5RV was ballparking his measurements,
since an antenna tuner is used to fine-tune the system...

Bob
k5qwg

Robert Kole wrote:
"Put another way, should the overall length of the antenna be 102 feet
or 102 ft. 3.33 in.?"

As Cecil noted, 3.33 in. is inconsequential in comparison with 102 ft.
Your antenna has bandwidth, and 3.33in. is only 0.3% of its length.
Given a tuner, the antenna system can be brought to resonance to remove
a reactive impediment to antenna current and radiated power.

A resonant dipole system is 1/2 wavelength or some multiple thereof. It
is a multiple of 180-degrees, tip to tip, and this includes loads, gaps,
coils, capacitors, and everything electrically making up the length. See
Chapter-8 "Dipole Antennas" in ON4UN`s "Low-Band DXing". Note that the
tip to tip dimension includes the feedline spacing in all illustrations.

Bob, K5QWG referred to Cebik`s analysis of the G5RV, a 102-ft. version
which is (3) 1/2-waves at 14.15 MHz. Note that Cebik also shows a
107-ft. version from the ARRL. Cebik notes that wire size and elevation
are more important than wire length when you are using a tuner.

Best regards, Richard Harrison, KB5WZI

Robert Cole wrote:
"Put another way, should the overall length of the antenna be 102` or
102` 3 1/3`` ?"

An example may be found in microwaves. The RSGB 3rd edition of "VHF-UHF
Manual" has a dipole dishfeed for the 23 cm band on page 8.67.

23 cm is 9 inches. The dipole is 4 & 7/16 inches tip-to-tip, or just 5%
short of 1/2-wavelength as expected for "end effects".

The tip-to-tip length of a dipole need not be adjusted for feedline
spacing.

Best regards, Richard Harrison, KB5WZI

In article , Richard
Harrison wrote:

[snip]

The tip-to-tip length of a dipole need not be adjusted for feedline
spacing.

Looking at graphs of how the waves form on the wire, that's what
I was thinking. But illustrations like the uppermost one on:
http://www.astrosurf.com/lombry/qsl-g5rv-2.htm
had me confused. I guess it's just wrong.

Robert Kole provided a link to a G5RV antenna attachment from
astrosurf.com. I enjoyed reading the attachment but I believe it
questionable when it says:

"---erect the antenna at an average height of about 10.35m (34 ft),
which happens to be the optimum efficiency on 160, 80 and 40m bands for
any horizontal type antenna"

"In practice few amateurs install masts of the optimum height on 80 or
40m, and certainly not on 160 meters."

I agree that often amateurs are limited to low mast heights, but not
being able to reach the heights needed (1/2-wave which eliminates energy
waste directly overhead) doesn`t make a lowered antenna optimum, just
feasible.

Best regards, Richard Harrison, KB5WZI