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940161.txt
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1994-11-13
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Date: Sat, 28 May 94 04:30:15 PDT
From: Ham-Ant Mailing List and Newsgroup <ham-ant@ucsd.edu>
Errors-To: Ham-Ant-Errors@UCSD.Edu
Reply-To: Ham-Ant@UCSD.Edu
Precedence: Bulk
Subject: Ham-Ant Digest V94 #161
To: Ham-Ant
Ham-Ant Digest Sat, 28 May 94 Volume 94 : Issue 161
Today's Topics:
"J pole" like antenna using coax instead of twinlead
(none)
Dipole in the trees!
help with 4 element yagi.. Please..
More on 10 meter dipole
Zip cord as antenna
Send Replies or notes for publication to: <Ham-Ant@UCSD.Edu>
Send subscription requests to: <Ham-Ant-REQUEST@UCSD.Edu>
Problems you can't solve otherwise to brian@ucsd.edu.
Archives of past issues of the Ham-Ant Digest are available
(by FTP only) from UCSD.Edu in directory "mailarchives/ham-ant".
We trust that readers are intelligent enough to realize that all text
herein consists of personal comments and does not represent the official
policies or positions of any party. Your mileage may vary. So there.
----------------------------------------------------------------------
Date: Fri, 27 May 1994 04:31:06 GMT
From: iglou!iglou!jmorton@uunet.uu.net
Subject: "J pole" like antenna using coax instead of twinlead
To: ham-ant@ucsd.edu
teacherjh@aol.com (Teacherjh) writes:
>In article <wa2iseCqDy47.1HI@netcom.com>, wa2ise@netcom.com (Robert
>Casey) writes:
> > Is there a design similar to the Jpole I can build
> > with these scraps of coax?
>There is a dipole that can be made by exposing the center element for
>one quarter wavelength, by folding back the shield for another
>quarter wavelength. I don't know all the details of it, perhaps
>someone could fill in. It also seems that there would be some
>interaction between the folded back shield and the unfolded shield it
>is going over, as a dipole is balanced, and coax is unbalanced.
>Jose KD1SB
I have built the antenna that Jose mentions and used them for emergency
antennas or suit-case antennas when traveling.
For a 2m antenna, strip off about 3 feet of the outer jacket to expose the
braid. Next, push the exposed braid so that it doubles over the jacket
remaining on the rest of the coax. At this point you end up with about
2 feet of braid that is now the outer layer of the coax and a 3 ft
section of the the center conductor extending out the end of the cable
away from the folded back braid. I usually cut the center conductor to
about 20 inches from where it enters the cable, strip off about 1.5 in
of insulation, make a loop in the end of it so that the center conductor
is about 19 inches from the tip of the loop to where it enters the cable.
The loop is there to make it easy to hang the antenna with a string. I
then "adjust" the length of the folded back for about 19 inches also, tape
it down, and put a connector on the thusfar untouched end of the cable.
Just a word to the wise. I said to start off with about 3 feet of the
outer jacket removed. It's going to surprise you how short that braid
is going to be when you roll it back over the cable's outer jacket.
BTW, a picture is worth.... Well, you know.....
John, WA4UMR
--
# John V. Morton jmorton@iglou.com wa4umr@w4cn.ky
------------------------------
Date: 27 May 94 19:52:29 GMT
From: news-mail-gateway@ucsd.edu
Subject: (none)
To: ham-ant@ucsd.edu
signoff
------------------------------
Date: Fri, 27 May 1994 14:42:00 GMT
From: ihnp4.ucsd.edu!swrinde!gatech!darwin.sura.net!news.duc.auburn.edu!lab41!gibsowc@network.ucsd.edu
Subject: Dipole in the trees!
To: ham-ant@ucsd.edu
I am planning to install an inverted vee for 160. 80, and 40 meters at my house
in the next week or two. I am planning on feeding it with 450 ohm ladder line and
an antenna tuner.
The problem with the setup is that I have nowhere to string the antenna except
from the top of the house, across the yard about 40 or so feet, and then into the
woods that are to the sides of the house. What effect will the trees around the
antenna (I'd say about maybe half of the antenna would be in the woods) have on its
performance? I'm thinking that the trees around it will create some sort of an
impedance problem at its end, but maybe some more knowledgeable folks could fill me
in.
73/dx
Walton C. Gibson, KE4FXN
gibsowc@eng.auburn.edu
------------------------------
Date: 26 May 94 11:50:44 EDT
From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!darwin.sura.net!wvnvms!marshall.wvnet.edu!desaid@network.ucsd.edu
Subject: help with 4 element yagi.. Please..
To: ham-ant@ucsd.edu
Hi antenna Gurus:
I am planning on making 4 element yagi for 2 meter (especially 145.01 or
145.05) radio to do packet and somtimes on other 2 meter frequencies (rarely)
I have following materials with me. Old TV antenna boom and elements of
various sizes. and a gamma match made up of alluminum pipe and RG-8 cable.
Size of gamma match is not yet determined.
Will someone tell how to go about construction of this 4 element antenna and
give some measurements for elements and gamma match that has worked for you.
I would greatly appreciate your help in this project. This is my first
project of antenna and I would like it to work.
Thanks a lot.
73, Dinakar kb8phz
------------------------------
Date: Fri, 27 May 1994 11:55:04 GMT
From: ihnp4.ucsd.edu!agate!spool.mu.edu!torn!nott!cunews!freenet.carleton.ca!FreeNet.Carleton.CA!am432@network.ucsd.edu
Subject: More on 10 meter dipole
To: ham-ant@ucsd.edu
In a previous article, HICKS.ALAN@epamail.epa.GOV (ALAN HICKS 617-860-4388) says:
> Finally, you bet that I didn't know exactly what "es" means in
> Morse code. Well, "es" comes from the Spanish word for "and".
> The ARRL Operating manual says it means "and" and that's how I
> use it. So "Gd luck es 73 de KD1DJ" would mean
I thought DIT DI-DI-DIT was the old landline (American) Morse ampersand.
Certain characters, like "P" and "&", had a space (different length)
embedded in the character.
--
========================================================================
Brice Wightman
Ottawa, Canada VE3EDR
========================================================================
------------------------------
Date: 27 May 94 19:49:39 GMT
From: news-mail-gateway@ucsd.edu
Subject: Zip cord as antenna
To: ham-ant@ucsd.edu
Jeff Herman asked about Zip cord as an antenna or transmission line. The
1988 edition of the ARRL antenna book presented an analysis of zip cord.
I'll quote the most interesting parts.
15-2 to 15-3
as an antenna:
"This information by Jerry hall, K1TD...QST for March, 1979"
"insulation left on the wire may have some loading effect so a bit of
length trimming may be needed fro exace resonance"
"use an electrician's knot that will keep the system from unqipping itself
under the tension of dipole suspension"
"But just how efficient is a zip-cord antenna system?...zip cord looks
about like 72-ohm balanced feed line. Does it work as well?
as a transmission line:
"100 foot roll was subjected to tests in the ARRl lab with an RF impedance
bridge"
"18 gauge, brown, plastic insulated type SPT-1".
"Characteristic impedance...107 ohms at 10 mhz, dropping in value to 105
ohms at 15 mhz and to a slightly lower value at 29 mhz. The nominal value
is 105 ohms at HF. The velocity factor of the line was determined to be
69.5%."
"Who needs 105 ohm line, especially to feed a dipole? A dipole in free
space exhibits a feed-point impedance of 73 ohms, and at heights above
ground of less than 1/4 wavelength the resistance can be even lower...80
meter dipole at 35 feet over average soil...35 ohms. Thus, for a resonant
antenna, the SWR in the zip-cord transmission line can be 105/35 or 3:1,
and maybe even higher in some installations."
"But the really bad news is still to come-line loss!" Fig. 3...attenuation
in db per hundred feed of line versus frequency. values based on
assumption that line is perfectly matched (sees a 105 ohm load as its
terminating impedance"
some values from the figure:
Frequency Attenuation, db per 100 ft.
3.5 0.75
7 1.75
10 2.5
14 3.9
21 5.6
28 7.2
Continuing:
"Additional losses over those charted in fig. 3 will occur when standing
waves are present. The trouble is, you can't use a 50 or 75 ohm SWR
instrument to measure the SWR in zip-cord accurately."
"In short, communications can certainly be established with a sip=-cord
antenna in a pinch on 160, 80, 40 30 and perhaps 20 meters. For higher
frequencies...long line lengths...the efficiency of the system is so low
that its value becomes questionable."
73 Mark KA3LFG
------------------------------
End of Ham-Ant Digest V94 #161
******************************