104 lines
4.7 KiB
Plaintext
104 lines
4.7 KiB
Plaintext
|
From edh@hpuerca.atl.hp.com Tue Mar 22 12:00:29 1994
|
||
|
|
Date: Tue, 22 Mar 1994 07:55:39 -0500
|
||
|
|
From: Ed Humphries <edh@hpuerca.atl.hp.com>
|
||
|
|
To: Stephen Dunifer <frbspd@crl.com>
|
||
|
|
Newsgroups: rec.radio.amateur.antenna
|
||
|
|
Subject: Re: 5/8 over 1/4 design info needed
|
||
|
|
|
||
|
|
Hi Stephen!
|
||
|
|
|
||
|
|
In rec.radio.amateur.antenna you write:
|
||
|
|
>
|
||
|
|
> Having read several references to 5/8 over a 1/4 vertical
|
||
|
|
>antenna, I have not been able to find any fully detailed construction
|
||
|
|
>plans in the usual sources. Can anyone provide the details or point the way
|
||
|
|
>to an appropriate source ? I assume that the antenna would consist of a
|
||
|
|
>5/8 element, 1/4 element and some sort of type of coil between the two
|
||
|
|
>elements along with the usual 4 ground radials.
|
||
|
|
|
||
|
|
If you are thinking about a collinear antenna, they usually have
|
||
|
|
1/2 wave elements stacked with 1/4 wave phase sections in between:
|
||
|
|
sometimes a carefully matched 5/8 wave section is used instead of 1/2.
|
||
|
|
|
||
|
|
However, from your description I suspect you are thinking about the
|
||
|
|
typical 5/8 wave antenna where the radiating portion sits on top of
|
||
|
|
a 1/4 wave _matching_ section (no radials required inthis configuration,
|
||
|
|
but may be added at the base of the 5/8 wave section (NOT base of the
|
||
|
|
matching section)). The most typical example of this is the Jpole.
|
||
|
|
|
||
|
|
So, if you'd like to have one of these, simple: build it from my
|
||
|
|
enclosed plans! I wrote this article several years ago (note: I
|
||
|
|
did not _design_ this, but written plans were pretty scurrvy before
|
||
|
|
I researched and wrote this. If you circulated the article further,
|
||
|
|
do please keep my name as author intact.
|
||
|
|
|
||
|
|
Many people have built this Jpole, literally from around the world!
|
||
|
|
|
||
|
|
The following article is 59 lines long.
|
||
|
|
Just cut at the "--cut here--" line and the article
|
||
|
|
will print neatly on one page for easy reference.
|
||
|
|
Hope you enjoy building and using!
|
||
|
|
Cheers & 73 Ed Humphries - N5RCK
|
||
|
|
Hewlett Packard NARC Atlanta GA
|
||
|
|
|
||
|
|
--cut here--
|
||
|
|
A Copper Tube J-pole
|
||
|
|
by Ed Humphries - N5RCK
|
||
|
|
edh@hpuerca.atl.hp.com
|
||
|
|
|
||
|
|
The following is a description of a J-Pole antenna made from copper
|
||
|
|
pipe. You can use 1/2 inch to 1 inch pipe (wall thickness will
|
||
|
|
affect stiffness/stability AND price, but not performance). Larger
|
||
|
|
diameter pipe increases bandwidth, but 1/2 inch is fine for amateur
|
||
|
|
frequencies. Start with a 10 foot (standard) length of pipe, 1 90
|
||
|
|
degree (right angle) fitting, 1 "tee" fitting, 2 end-caps, 2 hose
|
||
|
|
clamps (worm-gear adjustable of the appropriate diameter), and your
|
||
|
|
coax (end stripped, braid separated, center conducter stripped, and
|
||
|
|
coax sealant to close opening in coax to keep water out). Use a tube
|
||
|
|
cutter (for best/easiest results) and cut the 10 foot pipe according
|
||
|
|
to the dimensions needed following the diagram below:
|
||
|
|
__
|
||
|
|
| <=endcap
|
||
|
|
|
|
||
|
|
|
|
||
|
|
5/8 | for 146 MHz
|
||
|
|
|
|
||
|
|
|
|
||
|
|
wave |
|
||
|
|
|
|
||
|
|
|
|
||
|
|
|
|
||
|
|
-- | | <=endcap
|
||
|
|
| | 1/4
|
||
|
|
| | wave
|
||
|
|
| |
|
||
|
|
coax ctr conductor=>* *<= coax shield
|
||
|
|
| |
|
||
|
|
@ 5"-->| |
|
||
|
|
tee => --- <= elbow
|
||
|
|
|
|
||
|
|
| < "leftover" pipe
|
||
|
|
|
|
||
|
|
|
||
|
|
For best general purpose use, the 5/8th wave version should be
|
||
|
|
used. The dimensions to cut are: 66 1/2 inches (5/8 + 1/4 matching
|
||
|
|
section), 19 inches (other half of 1/4 matching section), 3/4 inch
|
||
|
|
(joins the tee and the elbow), and the "leftover" 33 3/4 inchs that
|
||
|
|
forms the base. Use standard plumbing solder methods to join main
|
||
|
|
section to base using the tee. Use the 3/4 inch piece and the elbow
|
||
|
|
to attach the 19 inch piece. Be careful to keep pieces parallel.
|
||
|
|
|
||
|
|
This will give you a center frequency of 146 MHz. Attach the coax
|
||
|
|
as shown using the hose clamps. Adjust the swr at 146 MHz by sliding
|
||
|
|
the connections up or down as needed -- you should be able to reach
|
||
|
|
very close to 1:1 (best to do this in approximately where you intend
|
||
|
|
to use the antenna - the base can be attached directly to a mast by
|
||
|
|
two hose clamps). Try not to be standing right by the antenna!
|
||
|
|
|
||
|
|
It has been noted that this design can lead to rf coupling onto the
|
||
|
|
feedline. To avoid this, put a ferrite on the coax at the feedpoint,
|
||
|
|
or use 3 turns (@1") of the coax taped together at the feedpoint.
|
||
|
|
|
||
|
|
Other center freq dimensions: (adjust 5/8 section accordingly).
|
||
|
|
144 =19.25 inches, 145 =19.12, 146 =19, 147 =18.86, 148 =18.73.
|