QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/antenna/940114.txt

Internet Message Format | 1994-11-13 | 20KB

Date: Thu, 21 Apr 94 04:30:12 PDT
From: Ham-Ant Mailing List and Newsgroup <[e-mail]>
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Reply-To: [e-mail]
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Subject: Ham-Ant Digest V94 #114
To: Ham-Ant


Ham-Ant Digest              Thu, 21 Apr 94       Volume 94 : Issue  114

Today's Topics:
                         Antenna Info needed
                  Calling all balun experts (3 msgs)
                 Ethernet Coax for Antenna? (2 msgs)
                   Is that all there is to a G5RV?
                Is this too crazy to work!!?? (2 msgs)
         Need recommendations on building an HF beam antenna
                           Skyprobe antenna
                        Slot antennas on cars?
                    Strange Coax Problem (2 msgs)
                        SW antenna info needed

Send Replies or notes for publication to: <[e-mail]>
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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: Wed, 20 Apr 1994 07:30:12 GMT
From: ihnp4.ucsd.edu!dog.ee.lbl.gov!agate!howland.reston.ans.net!cs.utexas.edu!chpc.utexas.edu!news.utdallas.edu!corpgate!bnrgate!bnr.co.uk!pipex!bbc!ant![e-mail]
Subject: Antenna Info needed
To: [e-mail]

Ky T. Nguyen ([e-mail]) wrote:
: Hi,

: I am looking for a Short Wave antenna for my Sony ICF-SW77.  I need a good
: antenna to get weak signal of BBC & VOA broadcasts which are directed to Asia.
: Anyone has one or knows about it, please give me suggestions and
: recommendations (which kind antenna I should buy).

: Thank you in advance for the information.

: [e-mail]

Try a random wire first. It's easier cheaper and if it doesn't work you
can always go out and buy a commercial product or build one. An antenna
tuner would help on the receive end of the random wire. Somewhat expensive to
buy, but you could probably build your own. Look in the ham books for
antenna tuning units. BTW I receive Nirobi wefax transmissions with a wire
strung across my loft.

Have fun

John B

[e-mail]

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

Date: 20 Apr 94 16:11:08 GMT
From: agate!overload.lbl.gov!dog.ee.lbl.gov!ihnp4.ucsd.edu!swrinde!emory!europa.eng.gtefsd.com!news.umbc.edu!eff!news.kei.com!ssd.intel.com!chnews![e-mail]
Subject: Calling all balun experts
To: [e-mail]

I needed two 4:1 baluns so I bought one Amidon HBHT200 voltage balun
designed by W2FMI and one MFJ-912 current balun designed by W9INN.
I compared them on an 88 ft. ABCD (all band centerfed dipole) and on
all the bands that I normally use, the antenna tuner settings were
the same, indicating that they were both doing a 4:1 transformation.

However, on a couple of bands, the antenna tuner (MFJ-949E) settings
were very different. On 10.125 MHz, the settings with the MFJ were

10  G  10  minimum Xc and a lot of Xl.  With the Amidon the settings:

10  C   4  less Xc on the output and less Xl.

I think one of these baluns is malfunctioning (saturating?) on 30m.
Question is, which one?  I plan to do some signal strength readings
when I get time. Receive signal 'S' meter readings were the same
with both baluns during this testing. Any ideas?

Thanks and 73, Cecil, KG7BK

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

Date: 20 Apr 94 16:36:09 GMT
From: dog.ee.lbl.gov!overload.lbl.gov!agate!howland.reston.ans.net!vixen.cso.uiuc.edu![e-mail]
Subject: Calling all balun experts
To: [e-mail]

In <2p3k6s$[e-mail]>, [e-mail] (Cecil A. Moore -FT-~) writes:
>I needed two 4:1 baluns so I bought one Amidon HBHT200 voltage balun
>designed by W2FMI and one MFJ-912 current balun designed by W9INN.
>I compared them on an 88 ft. ABCD (all band centerfed dipole) and on
>all the bands that I normally use, the antenna tuner settings were
>the same, indicating that they were both doing a 4:1 transformation.
>
>However, on a couple of bands, the antenna tuner (MFJ-949E) settings
>were very different. On 10.125 MHz, the settings with the MFJ were
>
>10  G  10  minimum Xc and a lot of Xl.  With the Amidon the settings:
>
>10  C   4  less Xc on the output and less Xl.
>
>I think one of these baluns is malfunctioning (saturating?) on 30m.
>Question is, which one?  I plan to do some signal strength readings
>when I get time. Receive signal 'S' meter readings were the same
>with both baluns during this testing. Any ideas?
>
>Thanks and 73, Cecil, KG7BK

A good test of saturation is running the balun at high power for a
longer period of time (preferably when bands are dead). If the balun
is not hot, it does't absorb the energy and thus is good. If the power
does not stay in the balun, it has to go somewhere!
Baluns are not ideal transformers but rather transmission lines.
Because their characteristics could be different, their performance
under mismatch is likely to be different from each other even if both
are perfect.  If your antenna is not perfectly balanced (one side is
closer to buildings/trees than the other), baluns may not isolate the
antenna from the ground.  The level of that isolation is considered
better for current than voltage baluns.

Ignacy Misztal              Ham radio: NO9E, SP8FWB
E-mail: [e-mail]
University Of Illinois      1207 W. Gregory Dr., Urbana, IL 61801, USA
tel. [phone]         Fax: [phone]

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

Date: 20 Apr 94 19:08:12 GMT
From: agate!howland.reston.ans.net!usc!nic-nac.CSU.net!news.Cerritos.edu!news.Arizona.EDU!nelson.as.arizona.edu![e-mail]
Subject: Calling all balun experts
To: [e-mail]

In article <2p3k6s$[e-mail]> [e-mail] (Cecil A. Moore -FT-~) writes:
>I needed two 4:1 baluns so I bought one Amidon HBHT200 voltage balun
>designed by W2FMI and one MFJ-912 current balun designed by W9INN.

Cecil, I've been under the impression that the W9INN balun is a voltage,
not a current balun. I could be wrong - a first this year.  :)


Howard

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

Date: 20 Apr 94 15:28:43 GMT
From: agate!library.ucla.edu!europa.eng.gtefsd.com!news.umbc.edu!eff!news.kei.com!ssd.intel.com!chnews![e-mail]
Subject: Ethernet Coax for Antenna?
To: [e-mail]

James Baker ([e-mail]) wrote:
: Does anyone have experience using IEEE 802.3 "thicknet" cable for antenna
: feeds?

Hi James, AT&T Ethernet cable has very similar loss characteristics to
RG-8 Foam. It's very good for HF and not bad for VHF. Only thing, it is
not UV resistant so if it's in the sun, it doesn't last very well.

73, Cecil, KG7BK

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

Date: Mon, 18 Apr 1994 14:43:05 -0800
From: ihnp4.ucsd.edu!swrinde!gatech!newsxfer.itd.umich.edu!ncar!asuvax!pitstop.mcd.mot.com!mcdphx!schbbs!mothost!mdisea!uw-coco!nwnexus!bellevue-ip16.halcyon.com![e-mail]
Subject: Ethernet Coax for Antenna?
To: [e-mail]

Does anyone have experience using IEEE 802.3 "thicknet" cable for antenna
feeds?

I am thinking about using it for HF longwire antenna leadin from Balun. It
is bright yellow, 50 ohm, well sheilded (two foils and 2 braid layers), has
one 12 ga. solid center conductor, attaches easily to PL-239's. Plus I have
a bunch otherwise going to waste.

Seems like the perfect stuff but I thought I might save myself some grief
if my plans are doomed for some reason I don't see.

Thanks for any input.

--
James Baker
Seattle, WA
[e-mail]

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

Date: 19 Apr 1994 22:00:38 GMT
From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!europa.eng.gtefsd.com!news.umbc.edu!eff!news.kei.com!ssd.intel.com!chnews![e-mail]
Subject: Is that all there is to a G5RV?
To: [e-mail]

Jim Garver ([e-mail]) wrote:

: Go out and buy the ARRL Antenna Compendium, Vol. #1, and read the article
: in there authored by Mr. Varney, AKA G5RV.  This should clear up any
: misunderstandings of his design.

Hi Jim, I think that's the article where Mr. Varney said to get rid of
the coax in a G5RV. The confusion is that all commercially available
"G5RV"s that I know of, come with coax.

: I have never tried the G5RV with coax and/or balun.  Only ladder line of
: the plastic 450 ohm species. [e-mail]  WA7LDV

There are some who will argue that it's not a G5RV without coax and a
"matching section". I wish we would just call these kinds of antennas
ABCFDs for All-Band Center-Fed Dipoles.

Thanks for remembering where I read Mr. Varney's latest recommendations.

73, Cecil, KG7BK

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

Date: Wed, 20 Apr 1994 07:41:47 GMT
From: ihnp4.ucsd.edu!swrinde!cs.utexas.edu!chpc.utexas.edu!news.utdallas.edu!corpgate!bnrgate!bnr.co.uk!zaphod.axion.bt.co.uk!uknet!lyra.csx.cam.ac.uk!pipex!bbc!ant![e-mail]
Subject: Is this too crazy to work!!??
To: [e-mail]

Bruce Pea ([e-mail]) wrote:

: I'd like to thank everyone who took the time to send me comments
: on my chicken wire counterpoise question. Now I've got another
: question.

: I'm thinking of building a half-wave helically <sp> wound 160m
: vertical to stick on top of my three story house. Can I use my
: water pipes in the house as my counterpoise? What if I attached
: ground wires to the pipes and ran them out in the yard and around
: the house, would that help even more?

: Does having the antenna three stories abouve the counterpoise make
: any difference? Is this too crazy to work? Is my ignorance obvious?
: Can you tell I JUST got my ticket and I'm going nuts trying to
: figure out what to put up :-)

: Thanks again for all your comments and help!

: Bruce / N9WKE

Let's say that your house is what 45 feet high in meters that's about 14m.
The wavelength at 160m is of course believe it or not 160m so we are
taling about say a lambda/10 gap. It might just work. You don't mention what
type of soil do you have. FYI the beeb use earth mats in the ground around
some lf/mf transmitters. So your idea of a earth wires doesn't sound so
crazy. I suggest you try the helix first and then add the improvements as
necessary. It was suggested to me a couple of days back that if you had a
CB lambda/4 whip on top of the car the capactiance between between the car
car and the ground would be sufficient to have the ground act like a
counterpise. Sounds like a similar problem to your own just a different scale.

Have loadsa fun.

John B

[e-mail]

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

Date: 20 Apr 1994 02:07:33 GMT
From: ihnp4.ucsd.edu!mvb.saic.com!news.cerf.net!usc!howland.reston.ans.net!vixen.cso.uiuc.edu!prairienet.org![e-mail]
Subject: Is this too crazy to work!!??
To: [e-mail]

I'd like to thank everyone who took the time to send me comments
on my chicken wire counterpoise question. Now I've got another
question.

I'm thinking of building a half-wave helically <sp> wound 160m
vertical to stick on top of my three story house. Can I use my
water pipes in the house as my counterpoise? What if I attached
ground wires to the pipes and ran them out in the yard and around
the house, would that help even more?

Does having the antenna three stories abouve the counterpoise make
any difference? Is this too crazy to work? Is my ignorance obvious?
Can you tell I JUST got my ticket and I'm going nuts trying to
figure out what to put up :-)

Thanks again for all your comments and help!

Bruce / N9WKE

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

Date: 20 Apr 94 06:02:55 GMT
From: agate!library.ucla.edu!europa.eng.gtefsd.com!news.msfc.nasa.gov!elroy.jpl.nasa.gov!wp-sp.nba.trw.com!newswire.etdesg.TRW.COM![e-mail]
Subject: Need recommendations on building an HF beam antenna
To: [e-mail]

>I'm interested in building a beam antenna for my new HF rig (Kenwood 850).
>After looking at the ARRL antenna book, I realized that I need some
>assistance.  I have some space to put up an antenna on my roof, but the
>kind of multi-band HF antennas that are shown in the book are ENORMOUS.
>Some of them are about the area of my house!

In addition to the usual antenna references, there was a
construction article in QST April 93 on a 2 element duoband beam.

An alternative which may be of interest is the 8JK antenna, a 2
element multiband beam. The latest literature I have seen is June
82 QST.  The antenna often uses open wire feed to a tuner to
accomplish multiband operation.  For a 20 meter through 6 meter
antenna, the elements are each 24 ft, spaced 8.5 ft.

While this is not a miniature antenna, the 24 foot element length
is just a little longer than a 15 meter full sized beam.  The
antenna is bidirectional, but has good front/back to side
rejection.  The mechanical aspects should be simpler than
building a trapped, multiband beam.

I built a version many years ago using a 2x2 fir boom which had
end pieces such that there was a wooden "H".  The aluminum
elements were mounted with standoff insulators on the wooden "H".

--wayne W5GIE
  "Speaking for myself"


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

Date: 18 Apr 94 19:37:31 GMT
From: agate!howland.reston.ans.net!cs.utexas.edu!usc!nic-nac.CSU.net!charnel.net.csuchico.edu!charnel!yeshua.marcam.com!news.kei.com!ub!newserve!sarah!psinntp!psinntp!halon!sybase!srikant@ucbvax.
Subject: Skyprobe antenna
To: [e-mail]

any idea where I can get this (in the SFO Bay area)? I checked with Ham Radio
Outlet (Oakland) and they don't carry this brand.

Thanks.
--
Srikant Subramaniam.
[e-mail]

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

Date: 20 Apr 94 05:26:33 GMT
From: agate!ihnp4.ucsd.edu!usc!elroy.jpl.nasa.gov!grian!pelican!ent-img.com!wb6hqk![e-mail]
Subject: Slot antennas on cars?
To: [e-mail]

In article <[e-mail]>, Alan Bloom <[e-mail]> wrote:
>
>The front or rear window of a car makes a pretty decent slot antenna for
>the CB band (or 10 meters).  It's shorter than resonant, but those who
>have tried it tell me that a small variable capacitor in series with the
>feed gives a low SWR.
>
>Connect the coax shield to the bottom of the window frame and connect
>the center conductor through the capacitor and a wire to the top of the
>frame at the middle.
>
Twenty or so years ago I successfully loaded the center window on the Port
side of a VW bus on 10m in the fashion Al describes.  As I recall I used a
small 50 pf variable cap on 28.585 MHz and it worked remarkably well compared
to a full 1/4 wave whip.  Never was able to shunt feed the entire bus
on 40m however....

BTW, the General Motors Impact Electric Vehicle uses an annular slot on
the roof for the FM (and AM I think) antenna.  Really works great!

bart   wb6hqk

[e-mail]

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

Date: 20 Apr 94 16:21:59 GMT
From: agate!howland.reston.ans.net!europa.eng.gtefsd.com!news.umbc.edu!eff!news.kei.com!ssd.intel.com!chnews![e-mail]
Subject: Strange Coax Problem
To: [e-mail]

Bob Dixon ([e-mail]) wrote:
: I have a 100 foot length of coax running up my tower that has gone bad in some way
: I do not understand. Measured with an ohmeter, both conductors show very low
: resistance. It measures infinite between conductors. Yet when a dummy load is placed
:                                      Bob W8ERD

Hi Bob, I had a problem with identical symptoms. My RG8X foam coax had been
too long in the Phoenix sun and the foam had melted. The center conductor
moved closer to the shield, not enough to short out, but enough to cause
an impedence mismatch and high SWR. I replaced it with 9913.

73, Cecil, KG7BK

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

Date: 20 Apr 94 19:39:03 GMT
From: hp-cv!hp-pcd!hpcvsnz![e-mail]
Subject: Strange Coax Problem
To: [e-mail]

Bob Dixon ([e-mail]) wrote:
: I have a 100 foot length of coax running up my tower that has gone bad in some way
: I do not understand. Measured with an ohmeter, both conductors show very low
: resistance. It measures infinite between conductors. Yet when a dummy load is placed
: at one end, the SWR is greater than 3:1 on all HF bands. All test equipment is known

etc.

As another poster noted, checking such a line with a TDR (or simple home-made
equivalent if you have a fast scope) would be a good idea.

One possibility is that the center conductor is no longer centered.
Particularly in polyethelene insulation, and especially if it's foam,
this can happen because the line has gotten hot.  One way it can get
hot is from operation at high SWR, and in this case, the heat tends
to concentrate at 1/2 wave nodes, causing a "ripple" effect in the
impedance vs length.  Just how much effect does a displacement of the
center conductor have?  Perhaps the following table, calculated from
a line formula in "Reference Data for Engineers"  (Sams), will be useful.
It's for a line insulated with solid polyethelene, dielectric constant
= 2.25 assumed, and center conductor OD = .2865 * outer conductor ID.
Displacement is in percent of outer conductor ID.

disp. % |  impdeance, ohms
--------|-----------------
    0   |    50.00
    5    |    49.56
   10   |    48.21
   15   |    45.83
   20    |    42.17
   25    |    36.73
   26    |    35.35
   27    |    33.83
   28    |    32.17
   29    |    30.32
   30    |    28.26
   31    |    25.93
   32    |    23.24
   33    |    20.05
   34    |    16.04
   35    |    10.29

(shorted beyond 35.67%)

73, K7ITM

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

Date: 20 Apr 94 18:42:18 GMT
From: [e-mail]
Subject: SW antenna info needed
To: [e-mail]

Hi,

I am looking for a Short Wave antenna for my Sony ICF-SW77.  I need a good
antenna to get weak signal of BBC & VOA broadcasts which are directed to Asia.
Anyone has one or knows about it, please give me suggestions and
recommendations (which kind antenna I should buy).

Thank you in advance for the information.

[e-mail]

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

Date: Wed, 20 Apr 1994 04:02:10 GMT
From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!europa.eng.gtefsd.com!library.ucla.edu!news.ucdavis.edu!csus.edu!netcom.com![e-mail]
To: [e-mail]

References <[e-mail]>, <[e-mail]>, <[e-mail]>
Subject : Re: Egg beater?

J.D. Cronin ([e-mail]) wrote:
: In article <[e-mail]> [e-mail] (Glenn Thomas) writes:
: >I used an eggbeater on 2m mobile during a VHF contest shortly after the
: >(etc.)
: >I was quite impressed by the antenna.
: >
: >73 de Glenn [e-mail]

: What's an "eggbeater" antenna?

: 73...Jim  N2VNO

Jim - An "eggbeater" antenna is a 2 meter antenna that consists of
two loops mounted two loops mounted orthogonaly. It provides a signal
that is largly circular polarization straight up (good for satellites)
and mainly horizontal polarization twoards the horizen (good for
terrestrial SSB - also 2m DX) - Glenn [e-mail]

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

End of Ham-Ant Digest V94 #114
******************************