QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/antenna/940317.txt

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

Date: Thu, 22 Sep 94 04:30:17 PDT
From: Ham-Ant Mailing List and Newsgroup <[e-mail]>
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Subject: Ham-Ant Digest V94 #317
To: Ham-Ant


Ham-Ant Digest              Thu, 22 Sep 94       Volume 94 : Issue  317

Today's Topics:
                      2m antenna for apartment?
                   2m vertical in my tree - how to?
                  Discones as transmitting antennas
                       Ham-Ant Digest V94 #313
                    HF Loop antenna for sailboat??
                   I need antenna matching software
                        MFJ DUAL BAND MOBILE?
                         RS twinlead antenna
                        SAREX antenna design?
                       Slinky antenna anyone?

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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: 15 Sep 1994 16:26:02 GMT
From: ihnp4.ucsd.edu!news.cerf.net!rosebud.sdsc.edu!news.tc.cornell.edu!news.cac.psu.edu!news.pop.psu.edu!ra![e-mail]
Subject: 2m antenna for apartment?
To: [e-mail]

In article <35856q$[e-mail]> [e-mail] (Sean
Lester) writes:
> I would like to build my own 2m/440 antenna.  I live in
> an appartment so it must be inside.  I have a great location
> near a window on the second floor in FL.  Could anyone suggest
> an antenna that is fairly easy to build and would give me good
> results?  As most hams, I have little $$$ to invest.
>
> [tbe rest deleted]
>

   If I recall correctly, the Radio Handbook by William Orr contains a
design for a 2m/440 J-pole.  I never tried building it myself since I
don't own any equipment for 440 mHz.

   One warning about building your own antenna: it might not be cost
effective if you're going to build only one.  I designed and built a
``plumber's delight'' J-pole a few months ago, and although I never added
up the cost of all the materials, I think it probably cost me between $30
and $40 just to build the first one.  The reason is that you typically
have to over-buy materials.  However, I later built one for my
sister-in-law using the leftover pipe and plastic, so the cost per antenna
obviously dropped.

   For me, cost wasn't a consideration.  I just wanted to experience the
pleasure of building my own equipment.  This, of course, is one of the
best facets of the hobby.  I'll also add that the 2 meter band is a good
place to do antenna experiments since you don't need a lot of space to
build and use an antenna that's efficient, and has respectable gain.

   But if cost is the main consideration, here's my $20 solution:  Run to
your nearest ham radio store and purchase the MFJ 2m/400 magnetic mount
mobile antenna for about $15.  On the way home, stop by the food store and
purchase a circular steel pizza cooking sheet.  Stick the antenna in the
center of the cooking sheet, and place the assembly on a table top, or in
the attic.  BTW, the top of a refrigerator makes an excellent ground plane
at 2 meters, so you can skip the cooking sheet if you don't mind operating
in the kitchen.

-Dave
--
David Drumheller, KA3QBQ          phone: [phone]
Acoustics Division, Code 7140       fax: [phone]
Naval Research Laboratory
Washington, DC 20375-5350   e-mail: [e-mail]

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

Date: Wed, 14 Sep 1994 19:43:40 GMT
From: newsflash.concordia.ca!CC.UMontreal.CA!IRO.UMontreal.CA!clouso.crim.ca!hobbit.ireq.hydro.qc.ca!barde![e-mail]
Subject: 2m vertical in my tree - how to?
To: [e-mail]

In article [e-mail], [e-mail] (Bob Bronson) writes:
>The highest point of my lot is an oak tree.  It is a good 20' higher than
>my roof peak.  Two reasons for considering placement in the tree are: 1)
>homeowners assoc. prohibits antennas on roof, & in tree it will be
>somewhat hidden.  2) it's there and higher already.  Has anyone made tree
>installations?  I would interested in hearing about it.  I would expect a
>slight loss being mounted against a 5-8" dia. live tree trunk compared to
>free air.  I'm looking at something like the Cushcraft ringo ranger 2
>vertical.  Thanks for any comments,
>
>Bob B.    KE4PGM    [e-mail]
>


You can save your money and build a J-Pole with 300 ohms twinlead. I did that
for a Fox Hunt here (Transmitter hunting). It hides very easy and you will
be able to install it much higher in the tree. Try to hang it away from large
branches; you will have less attenuation.
Good luck Bob.
73 de Clem, VE2HQJ

---
   Clement Vaillancourt,                  Institut de Recherche d'Hydro-Quebec
   Analyste,                              Varennes, P. Quebec, Canada, J3X 1S1
   Informatique scientifique           Tel:[phone] Fax:[phone]
   Int: [e-mail]   Radio-Amateur: VE2HQJ@VE2CRL.#MTL.PQ.CAN.NA

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

Date: Thu, 15 Sep 1994 17:46:48 GMT
From: ihnp4.ucsd.edu!news.cerf.net!rosebud.sdsc.edu!news.tc.cornell.edu!news.cac.psu.edu!howland.reston.ans.net!swiss.ans.net!malgudi.oar.net!chemabs![e-mail]
Subject: Discones as transmitting antennas
To: [e-mail]

Yea, finally a technical posting that I have a slim chance
at posting an answer...  :-)

NON active antennas no matter what configuration all share
what I'm gonna call a resiprosity.  What this means is the
antenna has the same radiation characteristics when transmitting as it
does when receiving.

Construction features that affect the reception pattern have
the same affect on the transmission pattern.

Obviously, I'm not saying that you can use a 28 guage wire that works well
as a receiving antenna for a high power transmitting antenna.  Obviously
you can't because you are liable to melt the wire when you try to
send your 1MW ATV signal down it  :-)

By NON active I mean that you can't expect an antenna that has a built
in pre-amp for reception of weak signals to work as a transmitting antenna
providing 'gain' on your transmitted antenna.

I'll stand back and let the experts give a better reply.
--
  Vince Herried (KA8CTE); From Bitnet: [e-mail] or vjh21%cas.org@ohstmvsa
  Chemical Abstracts Service   [phone] x 2877
  P.O. Box 3012, Columbus, OH 43210-0012

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

Date: 21 Sep 94 17:48:43 GMT
From: [e-mail]
Subject: Ham-Ant Digest V94 #313
To: [e-mail]

Subject: Discones as transmitting antennas

[e-mail] wrote:
: Here are a few questions for discone users.  I have a
: whip, since I've been told RS is in reality selling a
: 'topless' discone, unlike the Diamond discone which has
: the 'complete' discone with base-loaded vertical whip.
: that is, how close to the horizon is it?
:   2. Does the pattern change with frequency, and if so, how?
:   3. Does having a vertical element affect this pattern?
:   4. Should the vertical element be trimmed to work well
: on 2M/70cm?
:   5. Would I be better off simply removing the vertical element?
: The ARRL antenna book has plans for a homemade discone, without
: vertical element, and this leads me to suspect the vertical
: element is for enhancing receive capability (for scanners)
: I would very
:much like to use the discone
:for now as my  primary 2M/70cm transceiving antenna, as well as
: continue to use it as my scanner antenna.  I've polled this
: newsgroup recently about the discone vertical-element question
:  before.........
    >>>stuff deleated <<<<
:    Thanks.  --Bill   KB8USZ

  1. The discone is an antenna which exibits low angle radiation /
    reception above the frequency for which it is designed. Addition
    of the vertical element atop the disk is intended to add response
    to the structure at a lower frequncey than that for which the
    structure responds. the additional element will add a narrow band
    peaked response to the antennas performance for the frequency at
    which it is tuned. It will probably add distorting responses to
    the pattern at harmonics of the frequency to which it is tuned.

    2.The discone structure itself has a pattern which is independent
    of frequency over a broad range.

    3. Yes the vertical element effects patterns and frequency at
    which the antenna may be used. The size of the discone determines
    the lowest frequency at which it will work as a broadband antenna.
    I first saw the antenna written up for ham use in a cq magazine
    anthology which refered back to a 1948 edition. That version was
    for use from below 20 meters up. If you address the structure and
    support of the disk adequatly you could have a single antenna
    which could conceivably cover all ham bands with a constant
    impedance and gain. Also the center of radiation is based on the
    feedpoint's location.

    4. For any frequency where the vertical element affects the
    performance of the antenna, the structure is not opperating as a
    discone but as some sort of "corrupted ground plane antenna"
    You can make the structure function at frequncies for which the
    disk and skirt are not large enough but think of the structure as
    a ground plane antenna with a "funny/fat" vertical element. Note
    that the skirt may require extensions to provide adequate image
    response for the frequency to which the vertical element is
    resonated.

    5. I have seen double discones ie a structure with a disk in the
    middle and the skirt structure repeated above the "hot" disk as
    well as below it. The advantage is 3 dbd gain at the expense of
    a mechanicaly unweildy structure. Good frequency response for the
    scanner crowd but not very effective in terms of gain per
    buck/pound for the ham bands. The previous post regarding use of a
    J-pole ( which can be counstructed as a multiband antenna ) or
    other verticaly poloraized antenna will offer more performance in
    terms of specific frequency/band communciations.

    6. Accepting the lower gain of the discone in exchange for its
    broad bandwidth performance you should certainly be able to use
    the discone for 2m/70cm if it performs well as a scanner antenna
    above and below those frequencies and can handle the power ( most
    likely ) that you will appply. Good luck in your experimenting.

         ********************************************************
         *      Opnions expressed are mine and not Rockwell's    *
         *   73, K5VMU, Plano,Tx [e-mail]  *
         *********************************************************

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

Date: 21 Sep 94 09:14:07 -0400
From: ihnp4.ucsd.edu!dog.ee.lbl.gov!agate!howland.reston.ans.net!gatech!concert!hearst.acc.Virginia.EDU!alison.sbc.edu![e-mail]
Subject: HF Loop antenna for sailboat??
To: [e-mail]

In article <[e-mail]>, [e-mail] (Fernand Charron) writes:
>
> I am new with this newsgroup as well as a recently Ham (with full
> privileges).  I have a sailboat which I plan to sail down to the
> Bahamas next year and will intall on it my Kenwood TS450.  I
> currently use a 20m dipole as an antenna on the boat and my
> transceiver has an antenna tuner.  I don't seem to be able to
> transmit very strongly with this antenna even on 20 meters and
> reception of distant stations is good while local stations are
> usually weak.

My guess is that both your antenna and rig are working exactly
as they should.  What you are experiencing is perfectly normal
for 20 Mx.  Low power operation can be a real challenge on this
band and it is generally used as a DX band rather than for
local rag-chewing.  For strong local signals, you would probably
do better on 40 or 75 meters with the TS-50.  Also, you should
really expect only to operate on 20 with a dipole cut for the
band.  One thing that you do have going for you on 20 is the
Maritime Mobile frequency...I think it is 14.313.  You should be
able to get an answer there even if you were running very QRP.

73,
Ken
___________________________________________________________

       Kenneth D. Grimm                 K4XL
       [e-mail]
___________________________________________________________

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

Date: 21 Sep 1994 10:47:56 GMT
From: ihnp4.ucsd.edu!agate!howland.reston.ans.net!EU.net!Germany.EU.net!news.dfn.de!kfk.de!rz.uni-karlsruhe.de!news.uni-stuttgart.de![e-mail]
Subject: I need antenna matching software
To: [e-mail]

I am afraid that a wswr of 1.05 is far beyond the limit of what
can be measured correctly and what is really neccesary for
any transmitter around.

Bye for now, Moritz

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

Date: 21 Sep 94 09:53:29 EDT
From: psinntp!main03![e-mail]
Subject: MFJ DUAL BAND MOBILE?
To: [e-mail]

In article <Pine.SUN.3.90.940920092008.1173D-100000@daffyduck>, Hugh Shane <[e-mail]> writes:
>
> MFJ advertises a dual-band (2M/440MHz) mag mount for $14.95. Is it any
> good? (I don't think I could build my own so cheaply!)
[...]
It's junk. You're better off with a handheld and a rubber duck. I bought one a
while back, and promptly upgraded to a Comet B20 with a trunk lip mount. My car
has a sunroof, so I can't drill. :( What a difference.

I've also compared the mag mount to a homebrew 440 ground plane.
The GP wins easily (but it's harder to mount on a car!)
It only makes sense if you want to use it temporarily, with a mobile rig.
Otherwise, use your rubber duck.
--
Joe
[e-mail]

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

Date: Mon, 19 Sep 94 11:31:19 MST
From: agate!news.ossi.com!news.fujitsu.com!amdahl!pacbell.com!tandem!UB.com!kaiwan.com!news.claremont.edu!nntp-server.caltech.edu!ferrari.mst6.lanl.gov!tesuque.cs.sandia.gov![e-mail]
Subject: RS twinlead antenna
To: [e-mail]

On Mon, 19 Sep 1994 16:50:04 GMT,
Robert Adams  <[e-mail]> wrote:

>In article <[e-mail]>,
>Ross Frederick Blakeney <[e-mail]> wrote:
>>Hi, a little while back I noticed a posting about an antenna made with
>>radio shack twin lead over some other kind, if the person who made the
>
>If you're talking about the Folded Dipole it was my post. It's twice as
>broad as a single wire dipole... mine covers the entire 75m phone band
>under 2:1. But, I wouldn't recommend Radio Shack's twin-lead or coax on
>a bet.
>
>The radiator is made out of 120' of 450 ohm ladder line (the black plas-
>tic stuff with "punched windows") and a 4:1 current-type balun. You can
>order these from Radio Works (not "Shack") in Portsmouth, Virginia. Get
>ladder-line with stranded conductors - it's stronger.
>
>To fabricate, simply cut one side of the l-l in the center and install
>the balun. To keep strain off the joints you just soldered, tie a nylon
>line through a "window" on either side to the top eye ring - taughtly.
>Then, short each end of the l-l and install insulators. You're done!
>
>Feed it with 50 ohm coax. It's best installed as a shallow "V". Mine is
>at 55' with the ends at 35'. Works like a banshee.
>
>Robert Adams, P.E.
>[e-mail]
>[phone]
>
> * "FREE (the U.S. from) WILLY!" Vote Republican in November!
>
>
Robert, I agree with your voting habits, but I am not convienced that your
statements about the bandwidth of a folded dipole are correct.  There is no
reason for the bandwidth of a folded dipole to be wider than a normal DP
made of the same size wire.  If fact, full wave loops are generally
somewhat narrower in bandwidth than DP structures.  TRy any of the popular
antenna sofware to see the loop effect, not sure how to find out about
folded dipoles except to measure them and be sure the balum is not too
lossy as a lossy balum can make your SWR curve very broad (in the manner of
a dummy load).

William Osborne               505-646-3919
Professor ECE Dept.           PO BOX 30001, Dept. 3-O
New Mexico State University   Las Cruces, NM 88003-0001

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

Date: 16 Sep 1994 19:47:13 GMT
From: pa.dec.com!nntpd.lkg.dec.com!iamu.chi.dec.com![e-mail]
Subject: SAREX antenna design?
To: [e-mail]

I'm trying to find the design for the antenna that has been used in some
of the SAREX activities.  As I understand it, it is placed in a window
of the shuttle during operation.  Does anyone know where I could find
a copy or description of the design?

73,
Todd
N9MWB

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

Date: Tue, 20 Sep 94 15:56:52 GMT
From: olivea!charnel.ecst.csuchico.edu!csusac!csus.edu!netcom.com!netcomsv!skyld![e-mail]
Subject: Slinky antenna anyone?
To: [e-mail]

In article <[e-mail]> <[e-mail]> writes:

  >
  > Hi all, I recently saw in an old QST issue, Oct.1980, to be precise,
  > a ad for a slinky style antenna for 80/75, 40 and 20 meters.

  >                "looking for new ways to get that signal out..."


  Well, the newer slinky toys don't work as well. Plastic instead of copper
  plated steel. But, boy howdy, are they *colorful*!


 Amateur: WA6FWI@WA6FWI.#SOCA.CA.USA.NOAM | "You have a flair for adding
Internet: [e-mail]        |  a fanciful dimension to any
 US Mail: PO Box 4425 Carson, CA 90749    |  story."
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------------------------------

End of Ham-Ant Digest V94 #317
******************************