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VK2TV > HELP 03.04.07 14:36l 76 Lines 2915 Bytes #999 (0) @ WW
BID : 5F0056VK2TV
Read: GUEST
Subj: Re: Info, 1/2 Wave End Fed
Path: DB0FHN<DB0MRW<DB0SON<DB0SIF<DB0ROF<DB0ACH<DB0ACC<DB0GOS<ON0AR<ZL2BAU<
VK4TRS<KG6BAJ<WA7V<KD4YAL<VK2TV
Sent: 070403/0934Z @:VK2TV.#MNC.NSW.AUS.OC #:7385 [Kempsey, QF68JX] $:5F0056VK2
From: VK2TV@VK2TV.#MNC.NSW.AUS.OC
To : HELP@WW
ZL1ANM wrote:-
> From : ZL1ANM
> To : HELP@WW
> Type/status : B$
> Date/time : 03-Apr 10:23
> BID (MID) : ZL1ANM64
> Message # : 269501
> Title : Re: Info, 1/2 Wave End Fed
>
> Path: !KD4YAL!WA7V!SR1BSZ!IW2OAZ!ZL2BAU!ZL1AB!
>
> 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.
>
Actually, if you take the two-wire feed portion of the J-pole away at 90ø
to the 1/2 wavelength section, the antenna can, and does, find horizontal
application.
Such a feed method for an end-fed dipole is to be found in the literature
as the Zeppelin or Zepp feed.
The term is applied nowadays to any resonant antenna fed at the end by a
two-wire transmission line although it originally applied to end-feeding a
quarter wave antenna.
Keep in mind that the shorted, two wire feed (a stub), with the main
transmission line being "tapped" up the stub is nothing more than a
matching network of inductance and capacitance, the same thing that can be
achieved with discrete components ... provided you can calculate them.
Perhaps empirical methods are more practical!
Cheers ... Ray
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