--------- Begin forwarded message ----------
From: n4zc@juno.com
To: terry@qcislands.net
Cc: n4kg@juno.com
Subject: Re: Fw: 80m wire antenna ideas?
To: <towertalk@contesting.com>
Date: Tue, 16 Dec 1997 13:07:40 EST
Terry,
First, I'm NOT an antenna expert, I've just put up a number of 'em. (80M
LP ant)
Now, some things from the antenna book that you can use. Their idea of
using ropes between element ends so you only have to use 4 corner ropes
is a good idea. My first used ropes off each element which uses a lot
more rope. I've since changed the first one to just the 4 corner ropes.
This also makes it more easy to keep all alements in the same plane. I
also used their ideas for the open wire feeder and spacers to feed each
element.
If you build one of these, I sure woudn't use copper-clad steel wire like
I did with the first one....god what pain in the ass trying to keep the
wire from kinking., It's just too much wire to have that worry. I used
some wire I got from the wireman called "silky". You can role it out on
the ground and forget it. No worry about it trying to coil back up on
itself.
Another thing to keep in mind is not to put element tension on the
open-wire feeder or the crossover wires that give the 180 deg phase shift
from element to element. Wrap the element wire around the center spacer.
DON'T just go thru the hole and make the cross over as one continuous
wire without going thru the hole again to take the tension off the
crossover. Over time, the tension will pull the cross over wire down into
the open-wire feeder, shorting it out.
They show the elements swept forward like TV LP antennas. They were
wrong. They mixed apples and oranges there. TV antennas are swept forward
like that becaue they are using the elements in a harmonic length fashen
which does indeed give more gain that way....but the way they are used in
this article, they are half wave elements and you don't get more gain by
sweeping them forward like that.
Gain comes much more slowly per given boom length on the LP than say a
YAGI. You get about 3 db more gain when you double the YAGI boom
length...not so with the LP.
But of course the YAGI won't cover the CW/SSB parts of the band like the
LP.
I use .93 taper .08 space factors on my 60 deg and 270 deg LPs and .91
taper .08 space factor on the S LP. The orginal used the .91 .08 and
worked very well. When I rebuilt it and at the same time put up the new W
LP I decided to go for a bit more gain andc went with the .93 taper. It
covers the band OK from 3.5 to 3.9 mhz but starts to climb when you get
much above 3850, so when I put up a 180 deg LP I went back to the .91
taper to cover the band all the way up to 4 mhz. I don't go up there
myself, but some guys use my station in the SS contest and it's nice to
be able to go any place in the band during a domestic contest like that.
One of the nice things about the LP is once you decide on the taper
factor, the element lengths stay the same, no matter what space factgor
you use. So, once you decide how much of the band you want to cover, you
then look at how much space you have to decide the space factor and how
long you want the beam to be. While you have space for an optimum spaced
LP, I think I'd look at putting up two, back to back shorter LPs to cover
2 directions. I can design them to and boom length you want, but here are
a few examples
.93 taper
142' 132' 1" 122'10" 114'
.05 .08 .10 .17
14'2" 22'9" 28'5" 48'3"
13'2" 21'1" 26'5" 44'11"
12'3" 19'8" 24'6" 41'9'
.91 taper
142' 129'3" 117'7" 107'
.05 .08 .1 .17
14'2" 22'9" 28'5" 48'3"
12'11" 20'8" 25'10" 43'11"
11'0" 18'10" 23'2" 40'
There is only about 1.5 db more gain with the optimum .17 over the short
.05
space factor. LP gain comes faster with more taper factor than more space
factor.
Going from .91 to .95 taper would give the same amount of extra gain, but
at the cost of more elements or less band coverage.
More elements would allow a higher taper factor with more gain and still
cover the whole 3.5 to 4 mhz band. If you wish to use a higher taper
factor for more gain, I'll be happy to give you the info for any size LP
you would like to try. It would take 5 el for .93, 6 el for .94 and 7 el
for .95 to cover the whole 3.5 to 4 mhz band. Well, I guess I should also
say that if you are willing to give up a bit of front-to-back at the CW
end of the band, you could start with a back element of of say 138'
which would allow one less element for each taper factor. If you don't
work any CW, I could shorten it even more to cover just the phone band. I
guess I should have first asked you if you work CW. I can come up with
any size you want to cover the band you want to operate.
I'm retired and here most of the time in case you want to make a sked to
talk about antennas. I check my e-mail first thing every morning and just
before I go to bed, so no problem making a next day sked via e-mail.
73 Roger
On Mon, 15 Dec 1997 13:22:03 -0800 "Terry Mitchell" <terry@qcislands.net>
writes:
>Roger,
>Thank you for the reply. You are the only one who has reported success
>with
>the 80m LPDA. Below is my original message to towertalk. It contains
>pertinent info about my QTH. I think I have the height and space to
>put
>something good up in the air. Your success with the LPDAs has renewed
>my
>interest. I'm curious as to your particular design. Do you still use 4
>elements? and is the taper factor the only thing that you change? Are
>all
>of your LP 80m antennas the same? or have you improved the design with
>each
>new one. I look forward to your reply.
>73
>Terry, VE7TLL on NA051 'the Misty Isles'
>
>----------
>> From: Terry Mitchell <terry@qcislands.net>
>> To: towertalk@contesting.com
>> Subject: 80m wire antenna ideas?
To: <towertalk@contesting.com>
>> Date: December 8, 1997 9:22 PM
>>
>> I have recently been considering building the 80m log periodic
>dipole
>array
>> as described in the 18th edition of the ARRL Antenna Book.
>>
>> I do not currently have a tower but I do have pulleys at 95' in two
>trees
>> that are about 140' apart. The trees are in a north-south line and
>> completely clear around the bottoms of the trees. I live 1/2 mile
>from
>the
>> east coast of the Queen Charlotte Islands at sea level.
>>
>> I would appreciate any ideas for 80m antennas considering my
>situation as
>> well as comments on the 80m wire LPDA.
>>
>> Thank you and 73'3
>> Terry, VE7TLL on NA051
>
--------- End forwarded message ----------
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search
|