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KG6BAJ > NWSGRP 29.09.09 20:25l 33 Lines 1155 Bytes #999 (0) @ WW
BID : 12065_N1OES
Read: GUEST
Subj: Re: Open wire feedline
Path: DB0FHN<DB0NOE<DB0GAP<DB0GPP<DB0SEL<DB0ZDF<DB0LJ<DB0RES<DK0WUE<7M3TJZ<
XE1FH<AA6HF<KG6BAJ<KG6BAJ
Sent: 090929/0800Z @:KG6BAJ.#NCA.CA.USA.NOAM #:12065 [Grass Valley] InterGate $
** NEWSGROUP: rec.radio.amateur.antenna
** FROM : Cecil Moore <nospam@w5dxp.com>
Tim Shoppa wrote:
> But if you don't really need that 50 feet of feedline then why keep
> it? Straightest shot to the antenna will always be superior unless you
> want that extra 50 feet for impedance transformation or something
> else.
100 feet of ladder-line with an 80m dipole is easy to understand.
The dipole is 1/2WL. The ladder-line is ~1/2WL. The low 80m
feedpoint impedance tends to be reproduced at the shack end
thus making for an easy match.
However, 50 feet of ladder-line is ~1/4WL. The low 80m feedpoint
impedance tends to be transformed to ~4k ohms. Most built-in
autotuners will not handle such impedances.
100 feet of ladder-line is also a good length for multiband
operation of an 80m dipole as can be seen from this chart:
http://www.w5dxp.com/pnts130.gif
50 feet of ladder-line seems to be a good length for HF amateur
frequencies above 10 MHz - not so good for 80m and 40m.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
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