home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
QRZ! Ham Radio 4
/
QRZ Ham Radio Callsign Database - Volume 4.iso
/
digests
/
antenna
/
940251.txt
< prev
next >
Wrap
Internet Message Format
|
1994-11-13
|
11KB
Date: Mon, 8 Aug 94 04:30:14 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 #251
To: Ham-Ant
Ham-Ant Digest Mon, 8 Aug 94 Volume 94 : Issue 251
Today's Topics:
chimney mounted verticals
ftp's for antenna design needed
Ham-Ant Digest V94 #250 -Reply
how to build a single band vertical? (2 msgs)
JPole fundamentals
Ladder line length (was Re: G5RV grounding question)
MFJ vs. AEA IsoLoop?
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: Thu, 4 Aug 1994 14:18:43 GMT
From: nntp.ucsb.edu!library.ucla.edu!europa.eng.gtefsd.com!newsxfer.itd.umich.edu!zip.eecs.umich.edu!yeshua.marcam.com!usc!elroy.jpl.nasa.gov!lll-winken.llnl.gov!fnnews.fnal.@@ihnp4.ucsd.edu
Subject: chimney mounted verticals
To: ham-ant@ucsd.edu
I'd like to get some input on mounting a vertical on a chimney (traditional
TV antenna location). My chimney is in excellent condition and is
reasonably large (about 4 feet X 3 feet at the top). It is also about
33 feet tall. I am considering an R5 or R7 or GAP Eagle. Anyone have
experience (good or bad!) with this type of installation?
John Walker
N2ZGC/AA
ps. Just passed the code test at 13WPM. My test was multiple choice. IMHO
someone who is "stuck" at 10WPM could pass a multiple choice
test at 13WPM.
------------------------------
Date: 6 Aug 1994 12:52:24 GMT
From: ihnp4.ucsd.edu!news.acns.nwu.edu!math.ohio-state.edu!howland.reston.ans.net!europa.eng.gtefsd.com!sundog.tiac.net!news.sprintlink.net!tequesta.gate.net!inca.gate.net!optronic@network.ucsd.
Subject: ftp's for antenna design needed
To: ham-ant@ucsd.edu
If anyone knows where I can get some shareware programs for antenna
design, I would appreciate it. Also if you know of any good but
reasonably priced commercial programs (for PC) I'd like your opinions on
those too and where to buy.
Thanks, 73,
Bob B. KE4PGM optronic@gate.net
------------------------------
Date: 7 Aug 94 13:20:13 GMT
From: news-mail-gateway@ucsd.edu
Subject: Ham-Ant Digest V94 #250 -Reply
To: ham-ant@ucsd.edu
I'm on vacation until August 22. I'll read your message and reply
when I return. If you need assistance with Emission Monitoring or
Stack Testing, please contact Jerry Keefe or Jack Harvanek. Thanks
Alan Hicks
------------------------------
Date: 5 Aug 1994 16:23:29 GMT
From: ihnp4.ucsd.edu!ucsnews!newshub.sdsu.edu!nic-nac.CSU.net!charnel.ecst.csuchico.edu!yeshua.marcam.com!zip.eecs.umich.edu!umn.edu!newsdist.tc.umn.edu!uum1!aug2.augsburg.edu!petit@network.
Subject: how to build a single band vertical?
To: ham-ant@ucsd.edu
Most railroad antennas are 1/4 wave or the fire-cracker shortened
verticals (which are far less efficient than what you have). I recommend
the Larson LM-150 5/8ths vertical as high as you can get it. It will be
better magnetically mounted to the roof of your truck than hard mounted
to the toolbox. This antenna is about 40" tall and knocks the socks off
1/4 wave and scanner (wide band) antennas. A 1/2 wave antenna does not
have the impedance to match the coaxial cable and input to your receiver.
It is no more efficient than a 1/4 wave (whose impedance matches). For
160 Mhz your vertical element should be 18" long on a 1/4 wave ground
plane antenna. For information on a home-brew 5/8ths wave vertical see
the antenna projects chapter in the ARRL handbook. It requires a 36" rod
for a vertical element and a coil at the base of the antenna with about
10 turns of #10 or #12 wire. The coil must be made to withstand the wind
load on top of your car; which is why I recomment a commercial antenna
like the one from Larson.
In case you haven't discovered -- elevation is everything. Go to the top
of a hill and listen and you will hear far more than if you use any
exotic antenna. Most locomotive radios run 25 to 45 watts and have very
inefficient antennas (mobile units are about the same). You will hear the
dispatcher because they are on high towers, but will not hear the trains
beyond about 10 miles. If you go to the top of a hill, you will hear
trains, hand-helds, mobiles, defect detectors, etc. at distances far
greater.
------------------------------
Date: Sat, 6 Aug 1994 13:46:58 GMT
From: ihnp4.ucsd.edu!news.acns.nwu.edu!math.ohio-state.edu!cs.utexas.edu!convex!news.duke.edu!concert!hearst.acc.Virginia.EDU!saips.cv.nrao.edu!news.cv.nrao.edu!dwells@network.ucsd.edu
Subject: how to build a single band vertical?
To: ham-ant@ucsd.edu
In article <31tp21$qqm@aug2.augsburg.edu> Noel Petit
<petit@augsburg.edu> writes:
[some helpful comments about 5/8-wave whips and height deleted]
Sophisticated forms of mag-mount whips are appropriate for
automobiles, but for home use one might consider using even more
sophisticated antenna designs. Several years ago I asked a friend who
is an electrical engineer and who is active in 2-meter amateur radio
about high-performance 2-meter base station antennas. My thinking was
that the RR band is only 10% higher frequency than the 2-meter band,
so maybe we railfans can take advantage of the size and sophistication
of the 2-meter market.
My friend gave me a copy of an advertisement from Advanced Electronic
Applications (Lynnwood, WA, 206-775-7373) for their model ISO-144
"IsoPole" antenna; price in 1991 was $60. The antenna consists of
several conical elements stacked on top of each other along a mast 125
inches high; it has 50-ohm output impedance and apparently has no
ground plane elements. The ad asserts "maximum gain possible for [the
length]", "zero-degree angle of radiation for maximum range", "typical
SWR less than 1.4 to 1 or better across the entire band". Frequency
coverage is said to be 135-160 MHz, which just barely includes the RR
band at 160-161. It also says "2:1 VSWR bandwidth: 10 MHz @ 146 MHz",
but I don't understand whether or not that would be a bad thing (at
160-161 we would be more than 10 MHz from 146).
I am interested in putting an antenna on the roof of my house,
probably attached to the chimney, to operate with my scanner in the RR
band. Are the claims and specifications quoted above reasonable from a
technical point of view, and will an antenna like the one described
above give enough performance gain at 160-161 MHz to justify its price?
Are there better possibilities?
My friend also remarked "use a quality coax, can get losses". How
important is this factor, and are any types or brands especially
recommended? In my case, the cable run down through the attic to my
basement shop will be at least 50 feet.
--
Donald C. Wells Associate Scientist dwells@nrao.edu
http://fits.cv.nrao.edu/~dwells
National Radio Astronomy Observatory +1-804-296-0277
520 Edgemont Road, Charlottesville, Virginia 22903-2475 USA
------------------------------
Date: Sun, 7 Aug 1994 02:12:24 GMT
From: ihnp4.ucsd.edu!dog.ee.lbl.gov!agate!library.ucla.edu!csulb.edu!csus.edu!netcom.com!netcom16!faunt@network.ucsd.edu
Subject: JPole fundamentals
To: ham-ant@ucsd.edu
OK, one more question about this: Do any (or all) antenna analysis
programs successfully model a Jpole?
73, doug
------------------------------
Date: 5 Aug 1994 23:40:50 GMT
From: agate!howland.reston.ans.net!europa.eng.gtefsd.com!news.umbc.edu!eff!news.kei.com!ssd.intel.com!chnews!scorpion.ch.intel.com!cmoore@ames.arpa
Subject: Ladder line length (was Re: G5RV grounding question)
To: ham-ant@ucsd.edu
In article <31u5n9$2ri@newsgw.mentorg.com>,
John Bate <jbate@rtp-nc.mentorg.com> wrote:
>
>I am using 450 ohm ladder line on my 80 1/2 wave dipole fed by a 9:1
>balun. The balun is fed by a short (2') length of 50ohm coax.
>For some reason my SWR is very high (3-oo) on all bands except 10m.
>john (ki7hs/4)
Hi John, Consider the following discussion to be approximations only.
Assume your 80m 1/2 wave dipole has an impedance of 50 ohms on 4 MHz.
Your SWR will be 9/1 (450/50) and there's absolutely nothing wrong
with that SWR. 100 ft. of ladder-line is just about 1/2 wavelength
at that frequency taking velocity factor into account so your 9/1
balun is seeing about 50 ohms. 50/9 is 5.5 ohms so you also have
a 9/1 SWR on your 50 ohm coax and your transmitter will see that 5.5
ohms unless you have an antenna tuner. You will probably have a high
SWR on all bands... The only way you can get a low SWR is to have the
antenna impedance be near a purely resistive 450 ohms and I don't think
that happens on any band. You were probably just lucky on 10m.
I think you are assuming that if you have a 450 ohm transmission
line, you will be looking into 450 ohms at the generator end and that
is not a valid assumption. The impedance you see can be almost any
complex number on the Smith Chart and there's a bunch of 'em.
A combination of ELNEC and MicroSmith will model your antenna system
and give you an idea of what you are up against. You have a good,
efficient system there but your internal tuner may not have the range
to match what you need to match. If it does, quit worrying and enjoy.
If it doesn't, you need a broader range antenna tuner than the internal
one.
73, Cecil, KG7BK, OOTC (Not speaking for Intel)
------------------------------
Date: 7 Aug 1994 04:03:51 GMT
From: newsgate.watson.ibm.com!watnews.watson.ibm.com!fo!uri@uunet.uu.net
Subject: MFJ vs. AEA IsoLoop?
To: ham-ant@ucsd.edu
Hi,
Opinions and comments are sought: how do you
compare IsoLoop with MFJ 17<whatever it is>?
Experience? Is it really pain in the <there>
to tune the thing? Does it take forever to
sweep the band?
Thanks! [E-mail replies are appreciated.]
--
Regards,
Uri. uri@watson.ibm.com N2RIU
------------
<Disclaimer>
------------------------------
End of Ham-Ant Digest V94 #251
******************************