QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/antenna/940263.txt

Internet Message Format | 1994-11-13 | 19KB

Date: Tue, 16 Aug 94 04:30:17 PDT
From: Ham-Ant Mailing List and Newsgroup <[e-mail]>
Errors-To: [e-mail]
Reply-To: [e-mail]
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Subject: Ham-Ant Digest V94 #263
To: Ham-Ant


Ham-Ant Digest              Tue, 16 Aug 94       Volume 94 : Issue  263

Today's Topics:
                        6'x 9' chimney strap?
                   ftp's for antenna design needed
                 how to build a single band vertical?
           Should feedline lenght change the VSWR? (2 msgs)

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Problems you can't solve otherwise to [e-mail].

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: Mon, 15 Aug 1994 13:43:25 GMT
From: dog.ee.lbl.gov!overload.lbl.gov!dancer.ca.sandia.gov!cronkite.nersc.gov!osi-east2.es.net!lll-winken.llnl.gov!elroy.jpl.nasa.gov!usc!howland.reston.ans.net!gatech!wa4mei!@@ihnp4.ucsd.edu
Subject: 6'x 9' chimney strap?
To: [e-mail]

In article <32lrn4$[e-mail]> [e-mail] (Micro Demo Lab) writes:
>I've got a 25' flue on top of an 11 story apt. bldg.,
>and want to strap a mast & rotor for a KT-34A
>tribander.
>I'd like the mast to start at about 12' above the roof
>level and be stout enough to support me on step bolts.
>Ideally, a non-penetrating system and no contact with
>the roof is what I envision.
>The question: does anyone know of a ratcheting chimney
>strap that would fit the bill?
>To be able to climb the mast, I would need some sort
>of spacer and positioning it on a corner with some type
>of angle iron brace would hopefully provide the support.
>
>Any feedwack would be most welcome.

A note of caution. Masonry has great strength in compression,
but very little in shear. If you are going to add a moment
arm to the structure that places shear forces on the masonry,
you must do a proper structural analysis to determine if the
chimney will need structural bracing to withstand the side
loads.

A back of envelope guess says that you will. While I can't
offer structural engineering services by remote control,
I'll make a suggestion you can run by your structural
engineer. I'd put 4 inch angle iron on all four corners
of the chimney, connected together with torsion clamps.
Then you could probably safely mount your mast to one of
the corners as you propose. I'd use threaded rod clamps
rather than flexible strapping.

Let me reiterate the importance of getting proper structural
advice on this. At the height above ground this structure will
be, falling brick could be a *deadly* hazard. And you'll be
held liable, criminally so if you don't have a PE sign off
on this. Your insurance won't cover you either unless this
installation is done following codes and good engineering
practice.

Sorry to be a wet blanket, but people could be killed if
this installation is done wrong.

Gary
--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     | [e-mail]

------------------------------

Date: 15 Aug 1994 16:56:22 GMT
From: ihnp4.ucsd.edu!agate!howland.reston.ans.net!gatech!nntp.msstate.edu!olivea!koriel!male.EBay.Sun.COM!uranium![e-mail]
Subject: ftp's for antenna design needed
To: [e-mail]

In article [e-mail], [e-mail] (A. Amiet) writes:
.>In article <[e-mail]> [e-mail] (Raymond Anderson)
.>writes:
.>
.>                  ... stuff deleted ...
.>
.>
.>>You can obtain NEC2 (the real thing, "industrial strength") via anonymous
.>>ftp from:
.>>                ftp.netcom.com in /pub/rander/NEC
.>
.>>There is both source code and executables for Sun, IBM RS, Macintosh, and
.>>DOS based PC's. You will also find several NEC related utility programs
.>>there also.
.>
.>Errr....OK, tried that and even downloaded and ran nec-pc. It asks for an
.>input file. Oh. I didn't know what to tell it and so it naturally died. Could
.>you please (briefly) give a little bit of information about it and the other
.>programs on your area, such as what they do and how to make them work, as
.>readme type files are a little short on the ground.
.>
.>-a
.>
.>
.>
.>

The file that the program was prompting for was a NEC input file that describes
the geometry of the antenna. The specification of the file format is covered
in the program documentation available for purchase from the US Government.

It would be nice if someone had the time and expertise to distill the many pages of
documentation down to a concise users guide for the non-expert.

I don't have the official documents myself and have been using example program
files that are to be found with some of the implementations on the ftp site as
a guide to create my input files.

There is a document on the ftp site that describes how to obtain the official
documentation. I am including it below in this posting for general info to those
who are interested.

As far as documentation on other programs and utilities are concerned, most
have their own little .doc or .txt file included with them, and that is
all that is available. The authors of those utilities are identified along
with their e-mail addresses. Further inquiries could be made to the those
addresses if necessary.

There is a NEC related mailing list at  [e-mail] which is distributed
to a large number of NEC users world-wide. Questions posed to that group are
usually answered quite rapidly and accurately. Mail to [e-mail]
to subscribe to the list.

Here is the infor on ordering the NEC docs:

--------------------------included file starts here----------------------------
The following information provides the document numbers
and the address from which the official government documentation
for NEC2 may be ordered:

Numerical Electromagnetic Code (NEC) - Method of Moments

Volume I & II  NOSC TD 116       Order #  ADA 075289
Volume III     NOSC TD 116       Order #  ADA 075460

In 1994,  Vol I & II was $52 and Volume III was $27.
Normal delivery is $6.00 Rush fee was $15 each (in 1992), if you

If you don't need to rush, normal parcel post arrives within the same
week.

Note that the two volumes have the same NOSC numbers, but different
ADA document numbers.


Order Address:

U. S. Department of Commerce
National Technical Information Service
5285 Port Royal Road
Springfield  VA 22161

Phone: [phone]


(The above order information provided courtesy of Kok Chen <[e-mail]>)
(Updated 1994 info courtesy of Scott WB4YZA <[e-mail]>)


Note:
    Vol. I & II is Ops & Code
    Vol. III is User Manual

--------------------------------end of included file----------------------------

    I'd be glad to try to answer any specific questions relating to NEC,
but I am not an expert on it by any means.




73's de WB6TPU, Ray

----------------------------------------------------------------------------
This response does not represent the official position of, or statement
by, Sun Microsystems Incorporated.  The above data is provided for
informational purposes only.  It is supplied without warranty of any kind.
----------------------------------------------------------------------------

        /\
       \\ \
      \ \\ /
     / \/ / /      Raymond E. Anderson
    / /   \//\     Signal Integrity Engineer
    \//\   / /     Sun Microsystems
     / / /\ /      2550 Garcia Ave.  MS MIL04-16
      / \\ \       Mountain View, CA  94043-1100
       \ \\
        \/         [phone]
                   [phone] fax
                   [e-mail]
           [e-mail]

------------------------------

Date: 15 Aug 1994 16:20:32 GMT
From: dog.ee.lbl.gov!overload.lbl.gov!dancer.ca.sandia.gov!cronkite.nersc.gov!osi-east2.es.net!lll-winken.llnl.gov!koriel!cs.utexas.edu!howland.reston.ans.net!spool.mu.edu![e-mail]
Subject: how to build a single band vertical?
To: [e-mail]

In article <tad.775955594@jove>, Tad Marko <[e-mail]> wrote:
>Being a train nut, I built myself a magnet mount antenna tuned to 160.89
>MHz (the middle of the railroad band) consisting of a single vertical
>aluminum rod 3/16" in diameter and 1/2 wavelength long (adjusted for the
>diamter according to a talble from the ARRL antenna book). I also have
>one that is a full wavelength for when I'm train chasing through the
>countryside and a 10'6" tall vehicle isn't a problem.

Actually you are forgeting the matching coil and capacitor to make the
1/2 wave complete.  The 1/2 wave is very good since is doesn't require a
ground plane.  It has a more broad angle of radiation compared to a 1/4
wave or 5/8 wave with ground planes.  I can knife edge radio waves over
mountains for 80+ mile autopatch quality contacts at 1watt with a 1/2
wave end feed verticle.  (To have autopatch quality you can have some
white noise but requires good audio and no multipathing)

>
>I have the antenna mounted on my truck's toolbox, which is almost in the
>center of my full size pickup truck. This antenna works very well (and
>even pulls in 2m and of course the various even multiple and fractional
>bands as well), but I'm greedy for all the reception that I can get and
>was wondering if there was anything in the way of radials or any other
>tricks that I could do to improve the reception still more.
>
>Also, can anyone theorize on what the effective difference between the
>1/2 wave and full wave antennas may be?

1/2 wave dipole 0db, 1/2 wave verticle 2db, and 5/8 wave (with ground
plane) 3db gain.  The 1/2 wave vert is very good.  There is a type of
antenna that is called a ringo.  It is a verticle and can get 7 to 9db
gain but it is very long and acts as an array of antennas.

Hope this helps.

>
>Thanks,
>Tad
>
>--
>--
>Tad Marko            Internet: [e-mail]
>
>    If you really want to help me, give me Liberty.


* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
  Ryan McNeilly                    Internet: [e-mail]
KC7BYE
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

"You can't deal from a position of weakness"  --Alfred Thayer Mahan
Moral:  Protect the 2nd Amendment!

My comments and opinions are my own and nobody elses!!!!

------------------------------

Date: 15 Aug 1994 16:01:05 GMT
From: ihnp4.ucsd.edu!dog.ee.lbl.gov!overload.lbl.gov!dancer.ca.sandia.gov!cronkite.nersc.gov!osi-east2.es.net!lll-winken.llnl.gov!elroy.jpl.nasa.gov!usc!howland.reston.ans.net!gatech!@network
Subject: Should feedline lenght change the VSWR?
To: [e-mail]

In article <32hkca$[e-mail]>,
 <[e-mail]> wrote:
>
>Your analyzer is probably affected by the near
>field of the antenna and will give bad readings especially if it has a
>microcomputer in it. (I'm a microcontroller jock).

Oops, Steve, AB4EL, pointed out the error of my ways here. I was assuming
that the ham transmitter had to be on to make this reading. I obviously
knew nothing about the Autek RF-1. Steve tells me that it has a built-in
RF generator and therefore very little near-field radiation, certainly not
enough to affect the microcomputer. My statement applies to any measurement
attempted near the antenna with the ham transmitter power on. My apologies
to Autek Research, 4143 W. Waters Ave, no. 120, Tampa, FL 33614. The RF-1
is described in Aug QST page 47 and looks like a great antenna test and
tuning tool. Wish I had designed it.

73, Cecil, KG7BK, OOTC  (Not speaking for Intel)

--
 Intel, Corp.
 5000 W. Chandler Blvd.
 Chandler, AZ  85226

------------------------------

Date: Mon, 15 Aug 1994 14:11:44 GMT
From: dog.ee.lbl.gov!overload.lbl.gov!dancer.ca.sandia.gov!cronkite.nersc.gov!osi-east2.es.net!lll-winken.llnl.gov!elroy.jpl.nasa.gov!usc!howland.reston.ans.net!gatech!wa4mei!@@ihnp4.ucsd.edu
Subject: Should feedline lenght change the VSWR?
To: [e-mail]

In article <32m4rk$[e-mail]> [e-mail] (Stephen Modena) writes:
[I've deleted much of what Steve said, because I agree with most of it.]

>Now...let's turn to the idea that changing the length of the transmission
>line would change the SWR...well yes of course, in your case...it is
>almost unimaginable that the feed point of your antenna is 50 ohms
>resistive on any but a single frequency...but in fact, is probably
>never anywhere near 50 ohms over most of its operation range...and
>who knows what the reactive component is....
>
>It follows that a mismatch between the antenna
>feed point impedance and the surge (characteristic) impedance of the
>transmission line will result in the *transmission line* acting
>as an impedance *transformer*...and by definition, the nature of the
>impedance transformation is *dependant* the *length* of the coax.
>This stuff is in the ARRL Handbook briefly and in more depth in the
>Antenna Mannual.
>
>Depending on the actual degree of mismatch *and* the absolute values
>involved, it is *not* unusual for SWR values to *soar* when the
>transmission line length is at the *sharply* climbing regions of the
>Tan(h) function of impedance transformation.  Solution?  Lengthen or
>shorten the transmission line...or put an appropriate open-or-shorted
>shut about 0.1 wavelength from the antenna feed point to make the
>transmission line go flat...solutions that are easy on a single band
>but may require considerable experimentation when frequency hopping
>multiple bands is involved (as is the case of your multi-band antenna).


I don't think you intended to leave this impression, but it seems
you are saying that changing coax length will change the SWR on
the coax. That's false (aside from the relatively minor loss issues
already addressed by others). A transmission line transformer will
present a different impedance at it's generator end depending on
length and frequency, but the SWR on the line is wholely dependent
on the impedance of the antenna and the characteristic impedance
of the line. For any given mismatch at the antenna feedpoint, at a
given frequency, changing the length of the line will *not* change
the SWR on that line. A look at the Smith chart shows that when
using a transmission line as a transmission line transformer, you
rotate around a *constant VSWR circle* to get the impedance transformation
you desire. The distance around that circle is the length of line
you use. The SWR is *the same* at every point along the line.

>Now let's visit what the factory rep was trying to get across to you.
>
>Why not measure at the antenna (feedpoint)?
>
>Because you are interacting with the antenna by being there...because
>if you are interested in taming SWR with a noise bridge, reading
>at the antenna will not tell (inexperienced) you very much that *you*
>know how to *use*....this is not an insult: your post makes it clear
>that you do not have enough understanding to use at-antenna readings
>to advantage....that might not be the case for Roy Lewellen or me,
>but you are the one struggling along...hence it is better to watch
>the SWR at the point where it plugs into your transmitter when
>adjusting the antenna.

More to the point, a noise bridge *does not* measure VSWR. It measures
the presented impedance at that point along the transmission line
transformer. You have to work backwards with the Smith chart to
determine the true mismatch at the load and calculate the VSWR from
that.

Even if you were to use an actual VSWR measuring instrument, such
as a reflectometer, you'd still have the currents *on the outside
of the coax shield* to contend with. These will upset the VSWR
instrument reading. The velocity factor on the *outside* of the
coax shield is near 1 while the velocity factor *inside* the coax
is typically near 0.66, so the out of phase situation will vary
*along the length* of the cable. In fact, a good test for RF on
the *outside* of a coax cable is to take two VSWR readings at
different distances along the cable. If they differ by more than
can be accounted for by coax loss, you have RF on the outside of
the shield.  That's certainly the case here. The coax is acting as
part of the antenna radiating system.

Gary
--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     | [e-mail]

------------------------------

Date: 16 Aug 94 02:59:49 GMT
From: [e-mail]
To: [e-mail]

References [e-mail], (Robert, Wood)y
Subject : WILSON TOWERS

Anyone that used to work at WILSON or have a wilson
print that would list where WILSON tower parts were bought.
--  so I could get replacement parts.
--
73
===========================================================
Robert Wood
WB5CRG
[e-mail]        (blkbox is NOT blackbox, inc.!)
[e-mail]@menudo.uh.edu
============================================================

------------------------------

Date: Tue, 16 Aug 1994 03:18:00 GMT
From: gumby!wmu-coyote![e-mail]
To: [e-mail]

References <[e-mail]>, <32hhsg$[e-mail]>, <32onod$[e-mail]>▐
Subject : Re: Ever see a black tribander?

In article <32onod$[e-mail]>,
John Hays <[e-mail]> wrote:
>Black antennas are almost invisible to neighbors too ...
>

If they're wire antennas, down in the trees... but green would be better.
A black yagi, OTOH, would stick out like a sore thumb, lt. blue is better.

Personally, I couldn't care less what my neighbours thought. I paid for my
land... they didn't. <g>

Robert
WA9ZMO

 * Yagis should be mounted on stiff erections.

------------------------------

End of Ham-Ant Digest V94 #263
******************************