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ZL1ANM > HELP 03.04.07 02:14l 47 Lines 1873 Bytes #999 (0) @ WW
BID : ZL1ANM64
Read: GUEST
Subj: Re: Info, 1/2 Wave End Fed
Path: DB0FHN<DB0MRW<DK0WUE<F4BWT<IW2OAZ<ZL2BAU<ZL1AB
Sent: 070403/0010Z @:ZL1AB.#06.NZL.OC #:58471 [AUCKLAND] FBB7.00i $:ZL1ANM64
From: ZL1ANM@ZL1AB.#06.NZL.OC
To : HELP@WW
>> I find Nothing on matching the High Z of a 1/2 wave to 50 Ohms!
The J-pole is a popular end-fed 1/2 wave antenna. It is always
used in a vertical configuration, and is impracticable on the HF
bands because of its total height of 3/4 wavelength.
It consists of an upper (vertical) half-wave element to the bottom
of which is connected one side of a quarter-wave (vertical)
matching stub. The 50-ohm feed point is approximately 10 percent
of the stub's height, measured from the bottom of the stub, but
the exact position can be readily adjusted to achieve low SWR.
The antenna is therefore bottom-fed, with 50-ohm feed point being
about 50mm up from the bottom in the 145 Mhz version.
It seems to me that the J-pole's method of feed could be used in
a horizontal HF antenna, but I've never seen any literature on
the matter. Here's a suggested configuration:
|<---------------1/2 wave---------------->|<-----1/4 wave----->|
C B F A
_______________________________________________________________
_____________________|
F
The antenna may be especially suitable when the shack is on an
upper floor of a building and end-feed is the only option.
AC is a 3/4 length wire, with C representing an insulator at a
tree or pole. A represents an insulator attached to the building.
Suspended below AB on insulating spacers is the bottom half of the
matching stub AB. The feed point is FF, which should ideally be a
balanced feedpoint, but in the case of the J-pole is usually fed
directly with coax with very good results.
What say the experts. Can it work?
73 de Neil ZL1ANM
T4 1.5à24
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