QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/antenna/940241.txt

Internet Message Format | 1994-11-13 | 18KB

Date: Thu, 28 Jul 94 04:30:16 PDT
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Subject: Ham-Ant Digest V94 #241
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Ham-Ant Digest              Thu, 28 Jul 94       Volume 94 : Issue  241

Today's Topics:
               "Tuning" coax feedline lengths (3 msgs)
                          204CA dimensions?
                       Comet Miracle Baby CH-32
                       Feed lines and AC power
                           FM auto antenna?
                FREE tower,antenna,beam,rotator,cables
                     impedance of full-wave loops
                     Modelling 2 wire beverages.
                      R.Shack FM > 2M mod - Help
      Recommendations for 2M/70CM base station vertical antenna
                    What coax feed to us  (2 msgs)

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Archives of past issues of the Ham-Ant Digest are available
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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: 27 Jul 94 15:24:53 GMT
From: news.delphi.com!BIX.com![e-mail]
Subject: "Tuning" coax feedline lengths
To: [e-mail]

I was working a fellow in Florida the other day on 10M repeater
who insisted that coax feedlines should be full multiples, if possible,
of the wavelength of whatever frequencies they're going to be used for.
This is the first I've heard this, though I suppose there may be some
truth to it.   (I grant that I've seen a Smith Chart and how the
impedance you see looking in changes with distance down the line.)

But in general, is there any real merit to this fellow's claim?  Does
it really matter?  Enough so anyone should care?  For example, if you're
working 80M and find you really only need 20M of feedline, is there
anyone here who'd seriously coil up another 60M of coax, just to have
a full wavelength of it?

Also, it's pretty obvious that if yours is a multiband antenna, covering
12, 15 and/or 17M in addition to anything else, getting a common
multiple of the wavelengths is going to mean truly prodigious amounts
of coax!  Think of the line losses!

Anyway, to me this sounds like a lot of hot gas but then again, stranger
things have turned out to be true.  Comments welcome!

Regards,
Doug Hamilton    KD1UJ    [e-mail]    Ph 508-358-5715
Hamilton Laboratories, 13 Old Farm Road, Wayland, MA  01778-3117, USA


P.S.  This wasn't his only "interesting" idea.  He also insisted he was
buying some more land there in Florida so he could put up a 200 FOOT
FREESTANDING tower to get his Butternut vertical higher off the ground!

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

Date: 27 Jul 1994 16:19:06 GMT
From: overload.lbl.gov!agate!howland.reston.ans.net!usc!nic-nac.CSU.net!charnel.ecst.csuchico.edu!yeshua.marcam.com!news.kei.com!ssd.intel.com!chnews!scorpion.ch.intel.com!@@lll-winken.llnl.gov
Subject: "Tuning" coax feedline lengths
To: [e-mail]

In article <[e-mail]>,
hamilton on BIX <[e-mail]> wrote:
>
>I was working a fellow in Florida the other day on 10M repeater
>who insisted that coax feedlines should be full multiples, if possible,
>of the wavelength of whatever frequencies they're going to be used for.
>Doug Hamilton    KD1UJ    [e-mail]    Ph 508-358-5715

Hi Doug, the impedance in a transmission line repeats every half wavelength.
If the feedline is a full multiple, then (minus losses) you are seeing the
impedance of the antenna but that's usually not important. If the antenna
impedance is equal to the characteristic impedance of the transmission line
then the system is "flat" and any point in the line sees the same impedance
so the length is not important and the SWR is 1/1. (Disclaimer-for all
practical purposes :-)

Now where his statement would make sense would be when feeding a 50 ohm
antenna with 75 ohm coax and driving it with a 50 ohm transmitter. The
SWR would be 1.5/1 but if you make the transmission line an integral
number of half-wavelengths, your transmitter will see 50 ohms.

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

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

Date: Wed, 27 Jul 1994 21:50:12 GMT
From: ihnp4.ucsd.edu!sdd.hp.com!hp-pcd!hpcvsnz![e-mail]
Subject: "Tuning" coax feedline lengths
To: [e-mail]

hamilton on BIX ([e-mail]) wrote:

: I was working a fellow in Florida the other day on 10M repeater
: who insisted that coax feedlines should be full multiples, if possible,
: of the wavelength of whatever frequencies they're going to be used for.

..

: But in general, is there any real merit to this fellow's claim?  Does
: it really matter?  Enough so anyone should care?  For example, if you're
: working 80M and find you really only need 20M of feedline, is there
: anyone here who'd seriously coil up another 60M of coax, just to have
: a full wavelength of it?

Nope.  If the SWR is 1:1, you won't be able to tell any difference at
the feedpoint, and the only difference will be less loss with a shorter
lenght, as you suggest.  If it's not 1:1, all the more reason to keep the
loss low by keeping it short.  An integer number of halfwaves length
causes the impedance at the feedpoint to be (nearly) the same as the
load impedance, but there's nothing magic about that.  And of course,
if you _do_ want to use the line for matching (stubs in series and/or
shunt), then you want them specific lengths, accounting for the
propagation velocity in the line you use.

73, K7ITM

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

Date: 27 Jul 94 17:12:55 GMT
From: [e-mail]
Subject: 204CA dimensions?
To: [e-mail]

Howdy.  Anyone have the dimensions for the 204CA. If you'd be so kind
to e-mail them to me, I'd be ever so grateful.             73 de Walt
.............................................................................
73 de Walt Kornienko  -   K2WK    Internet:  [e-mail]
DX PacketCluster:  K2WK > W3MM    (FRC) Packet: [e-mail]
"My mother was of the sky,    My father was of the earth,
 But I'am of the universe,      And you know what that is worth." - J.Lennon
_____________________________________________________________________________

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

Date: Wed, 27 Jul 1994 16:58:49 GMT
From: elroy.jpl.nasa.gov!usc!howland.reston.ans.net!spool.mu.edu!news.clark.edu!netnews.nwnet.net!reuter.cse.ogi.edu!hp-cv!hp-pcd!hpcvsnz![e-mail]
Subject: Comet Miracle Baby CH-32
To: [e-mail]

What kind of experiences has anybody had using Comet's CH-32 Miracle Baby HT
antenna? I know it won't give me the same performance as the already
inefficient stock rubber duck that came with my HT but what can I reasonably
expect? Can I accomplish at 2 watts with the CH-32 what I can now do with
5 watts and my stock rubber duck or is the CH-32 a real dummy load?

Dave, KB7QCL

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

Date: 27 Jul 1994 13:53:58 -0500
From: ihnp4.ucsd.edu!news.acns.nwu.edu!math.ohio-state.edu!hobbes.physics.uiowa.edu!news.uiowa.edu!norand.com![e-mail]
Subject: Feed lines and AC power
To: [e-mail]

Hi all:

We have an run of 170 ft of underground coax at the "farm"/contest station.

We ran 3 runs of RG17, 3 of RG8, and a couple of runs of 16 pair data cable.  The
installation has been working fine for about 3 yrs now.

We ran the wires in 4in PVC with a slight slope toward the tower end.  At the
tower end we put in a T to bring up the coax, and ran another 8 ft of PVC out
past the tower (and down).  We put another T on the end and capped it.  The
T-hole on the end was pointed down and we filled in gravel under it to give any
water that infiltrates the pipe a place to drain.

Since the station is on a hill the whole mess underground is above the water
table.  I wonder if we will eventually have to replace waterlogged coax.  Last
fall we pulled out one of the RG17 sections and replaced it with a longer 1.  It
showed no sign on the jacket of any water infiltration.


You can get direct burial AC power wire and throw it in the hole next to the PVC.
I worry about RF coming back in the AC line, but have not seen any problems.
probablly due to the superb homebrew antennas ;)

The best part of the deal is now that the grass has grown back we don't have to
drag long runs of cable through the mud every time a contest comes around.  You
really appreciate a real installation after a couple years of temporary occupancy.

Good Luck

Guy
N0MMA
[e-mail]

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

Date: 27 Jul 1994 10:04:31 GMT
From: ihnp4.ucsd.edu!agate!library.ucla.edu!csulb.edu!csus.edu!mercury![e-mail]
Subject: FM auto antenna?
To: [e-mail]

Hope I am not intruding here with a question that does not pertain
strictly to amateur radio. I figure you are the experts so that's
why I'm asking you!
  I've been driving around for some time with my car antenna broken and
the reception has suffered. Is there an especially good antenna for
receiving FM broadcasts? (I've got an old Blaupunkt AM/FM radio cassette
deck that I bought second hand when my Honda Civic was new in 1983.)
  Any suggestion as to commercial antennas or homebrewing welcome!
  Thanks from a former electronics/radio hobbyist who occasionally
wishes he had the time to tinker again.
  If I need to supply more info, please let me know and I'll do so.

--
Paul Pederson
 Classics Department Student
  San Francisco State University
     [e-mail]

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

Date: 27 Jul 1994 01:38:36 -0400
From: agate!howland.reston.ans.net!gatech!concert!bigblue.oit.unc.edu![e-mail]
Subject: FREE tower,antenna,beam,rotator,cables
To: [e-mail]

>[e-mail] (Robert Cunitz) writes:
>
>Any reason that this whole setup would be free? You've got a call sign so
>you probably know what it could be worth!

We are redoing the yard and the tower is in the way.  I haven't used it
for some years.  Someone will have to work pretty hard to get it down and
cart it away.  OTOH, it will solve my problem without me having to pay
someone to do it.  Quid Pro Quo!!!
--
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Launchpad is an experimental internet BBS. The views of its users do not
necessarily represent those of UNC-Chapel Hill, OIT, or the SysOps.
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------------------------------

Date: Wed, 27 Jul 1994 19:16:55 GMT
From: ihnp4.ucsd.edu!agate!howland.reston.ans.net!torn!nott!cunews!freenet.carleton.ca!FreeNet.Carleton.CA![e-mail]
Subject: impedance of full-wave loops
To: [e-mail]

I've been hearing some good things about the Eggbeater antennas.
There was a review in QST last year of the commercial product, and more
recently an article in CQ.

I've been thinking of homebrewing one to give it a try.  I assume it
should be fed in a similar manner to a turnstile, with one loop fed 90
degrees out of phase using a quarterwave transmission line.

Could someone with one of those nifty antenna design applications tell me
what the input impedance of a SINGLE full-wave square loop would be at 145MHz
and 435MHz if constructed from say, insulated #12 house wiring?

I'm hoping it will be around 70 ohms, because that will be easy to match
using 1/4 wave coax sections.  If not, would going from a square to
either a rectangle or a loop bring the input impedance closer to 70 ohms?

tnx in advance for any assistance you may be able to render me.

de va3rr/aa8lu

--

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

Date: 27 Jul 94 17:14:54 GMT
From: [e-mail]
Subject: Modelling 2 wire beverages.
To: [e-mail]

Howdy.  Has anyone successfully modelled a two-wire beverage using
ELNEC or MININEC (or even NEC)?  I'd appreciate your wisdom. Thanx.
.............................................................................
73 de Walt Kornienko  -   K2WK    Internet:  [e-mail]
DX PacketCluster:  K2WK > W3MM    (FRC) Packet: [e-mail]
"My mother was of the sky,    My father was of the earth,
 But I'am of the universe,      And you know what that is worth." - J.Lennon
_____________________________________________________________________________

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

Date: Tue, 26 Jul 1994 23:19:27 -0400
From: pacbell.com!att-out!gw1!fnnews.fnal.gov!unixhub!lll-winken.llnl.gov!overload.lbl.gov!dog.ee.lbl.gov!agate!howland.reston.ans.net!torn!news.unb.ca!coranto.ucs.mun.ca!@@ihnp4.ucsd.edu
Subject: R.Shack FM > 2M mod - Help
To: [e-mail]

In article <313nml$[e-mail]>, Bob Bronson wrote:
> I was following a couple of threads several weeks ago on the mods to the
> Radio Shack FM antenna for 2 meter yagi.  Seeing notes from many people
> building these, I never saw the final posts of the results.  Would
> someone please e-mail me the final plans for this.  It sounded like a
> great project, I'd like to hear how it worked out for you.
>
> Bob Bronson   [e-mail]   KE4PGM

    Please post to this newsgroup. I never saw the final plans either.
Also, could you please comment on whether all the RS stores (in Canada)
carry this ant. model. My catalog is very old and it ain't in there.

Thanks,
____________________________________________________________

 Yvonne Dawe                      [e-mail]
____________________________________________________________

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

Date: 27 Jul 1994 21:05:11 GMT
From: pa.dec.com!src.dec.com!src.dec.com![e-mail]
Subject: Recommendations for 2M/70CM base station vertical antenna
To: [e-mail]

I'd appreciate recommendations on the above.

73,
Ira
KE6KHT

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

Date: Wed, 27 Jul 1994 15:56:41 GMT
From: spsgate!mogate!newsgate!dtsdev0![e-mail]
Subject: What coax feed to us
To: [e-mail]

Attribution lost, but likely [e-mail] writes:

>>   Have you ever tried 9880? We had lots of this stuff laying around from
>>an old ethernet network. I was always curious if this would also be very
>>good. it's 50 Ohm. looks like a Urathane dialectic.

[actually cellular polyethelyne]


In article <[e-mail]> [e-mail] (Mark Tetrault) writes:

>    Well, I'm using it for all my vhf/uhf work including a satellite
>array. It is extremely low loss, lower than 9913 but not quite as good
>as hardline.

  The Belden catalog only rates 9880 to 50MHz, where its loss is 1.2 db
per 100 ft.  At 50MHz, 9913 is only 0.9db (and ratings continue to 4GHz.)
Of course, if the price is right on the 9880, it would be an attractive
option.

-dave

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

Date: Wed, 27 Jul 1994 04:56:16 GMT
From: world!mv!mv.mv.com![e-mail]
Subject: What coax feed to us
To: [e-mail]

To: [e-mail]

In a recent message, you wrote;

Cecil,
>
>   Have you ever tried 9880? We had lots of this stuff laying around
from
>an old ethernet network. I was always curious if this would also be
very
>good. it's 50 Ohm. looks like a Urathane dialectic. solid copper
conductor
>(looks about 12 gauge). a foil layer followed by a 95%+ stranded weave
>followed by another foil layer followed by yet another 95%+ stranded
weave.

    Well, I'm using it for all my vhf/uhf work including a satellite
array. It is extremely low loss, lower than 9913 but not quite as good
as hardline. Be careful of vampire tap holes in used ethernet cable,
and be aware that the outer jacket has less UV protection than 9913, so
watch for outer jacket deteriotion.

    With that caveat, I would NOT hesitate to use it, and I do.

    Mark


---
* UniQWK v3.3a* The Windows Mail Reader

--
-------------------------------------------------------
| Mark D. Tetrault      | [e-mail]          |
| 6 Colonial Drive      | 1:132/[e-mail]       |
| Pembroke, NH 03275    | kd1vk @ wa1wok 44.52.7.8    |
| [phone]        | Have a Nice Day!            |
-------------------------------------------------------

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

Date: 27 Jul 1994 01:52:29 GMT
From: pacbell.com!well!barrnet.net!agate!howland.reston.ans.net!europa.eng.gtefsd.com!newsxfer.itd.umich.edu!zip.eecs.umich.edu!yeshua.marcam.com!news.kei.com!ssd.intel.com!@@ihnp4.ucsd.edu
To: [e-mail]

References <310mc0$[e-mail]>, <3127hb$[e-mail]>, <[e-mail]>a.eng.g
Subject : Re: What coax feed to use for 2m antenna

In article <[e-mail]>,
andrew peter.cropley <[e-mail]> wrote:
>
> Have you ever tried 9880? We had lots of this stuff laying around from
> an old ethernet network.  Andy Cropley

Hi Andy, don't know about 9880, but the Ethernet cable used here at Intel
(yellow and orange, AT&T 1 and 1A) has almost identical characteristics
to RG-8F which is better than RG-213 and not as good as 9913. The only
disadvantage is that it is NOT UV protected.

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

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

End of Ham-Ant Digest V94 #241
******************************