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ZL1ANM > HELP 06.04.07 04:57l 63 Lines 2374 Bytes #999 (0) @ WW
BID : ZL1ANM69
Read: GUEST
Subj: Re: Info, 1/2 Wave End Fed
Path: DB0FHN<DB0FOR<DB0SIF<DB0SON<DB0HBN<DB0SWR<DK0WUE<DB0RES<ON0AR<ZL2BAU<
ZL1AB
Sent: 070406/0250Z @:ZL1AB.#06.NZL.OC #:58609 [AUCKLAND] FBB7.00i $:ZL1ANM69
From: ZL1ANM@ZL1AB.#06.NZL.OC
To : HELP@WW
>From: K0CQ@W0AK.#CIA.IA.USA.NA
>To : HELP@WW
>
>The J is nothing more than a 30s era end fed Zeppelin with the
>feed line in line with the antenna.
Depends what your definition of "feed line" is. The J-pole's
quarter-wave matching stub is really a matching device with one
end shorted and with a tappable feed point. Is this the normal
configuration for a feed line? Its dimensions, except for its
length, are uncritical, unlike a true transmission line where
the spacing, conductor diameters (and dielectric) determine the
line's characteristic impedance.
>Since the feed line section
>is balanced it doesn't radiate much (almost not at all). Its a
>shorted quarter wave resonator fed near the shorted end. It
>connects to the end of a half wave dipole where the impedance is
>very high. Since that connected load is high that's not much
>different from the open on the other side so its pretty close to
>balanced.
Yes, although I think you're confusing the issue by continuing to
refer to the quarter-wave stub as a feed line.
>The J (pole) was used in the 1930s on VHF, its not new,
I find no reference to the J-pole, or its method of feed under some
other name, in either my 1936 or 1963 ARRL Handbooks. The earliest
reference I have is a detailed description of it in my ARRL Antenna
Book, 1974 Edition, pp 226-227 and 246-247. If you have an earlier
source, I'd be pleased if you would quote the reference.
>Its not
>all that good because it doesn't decouple the feed line from the
>antenna so it lets quite a bit of RF run down the coax and
>radiate like a really long wire looking radiation at the horizon
>when used at VHF.
The matching stub is balanced (as you yourself pointed out in an
earlier paragraph, above) and should really be fed with a balanced
feeder such as 300-ohm ribbon or 600-ohm spaced feeder, or via a
balun to 50-ohm coax. However many including myself, feed direct
with 50-ohm coax on 2m with very good results.
>You asked, "Can it work?" Yes it can, it has for at least 3/4
>century.
I've never seen any reference to a horizontally orientated J-pole.
Let's hear from experimenters about their results. I don't have
a backyard big enough.
73 de Neil ZL1ANM
T4 1.5à24
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