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1994-11-13
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11KB
Date: Sat, 21 May 94 04:30:13 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 #151
To: Ham-Ant
Ham-Ant Digest Sat, 21 May 94 Volume 94 : Issue 151
Today's Topics:
2m mobile antenna help!
HamSticks....
More AM Help...
Using 50ohm Coax instead of 75ohm
Why are there no amateur helix antennas? (2 msgs)
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: Fri, 20 May 1994 03:14:55 GMT
From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!agate!library.ucla.edu!csulb.edu!csus.edu!netcom.com!potaczek@network.ucsd.edu
Subject: 2m mobile antenna help!
To: ham-ant@ucsd.edu
------------------------------
Date: 21 May 94 03:56:20 GMT
From: agate!howland.reston.ans.net!wupost!udel!news2.sprintlink.net!news.sprintlink.net!news.onramp.net!usenet@ucbvax.berkeley.edu
Subject: HamSticks....
To: ham-ant@ucsd.edu
hamsticks are available direct from Lakeview 800-226-6990 for $19.95 ea plus
4.75 shipping. They are truly magic antennas.
They take visa/mc
-George Csahanin WB2DYB/5
------------------------------
Date: 21 May 94 06:17:05 GMT
From: agate!howland.reston.ans.net!math.ohio-state.edu!darwin.sura.net!mother.usf.edu!luna!shadrick@ucbvax.berkeley.edu
Subject: More AM Help...
To: ham-ant@ucsd.edu
Okay, as some of you may remember, I have been trying to get an AM
station from far away, and I needed to MAKE of BUY a loop antenna. Well,
I am still having some problems.
Could someone suggest a book or source I could look at that may help?
Sorry to be so dense on this subject. Thanks for your help.
shadrick@luna.cas.usf.edu
------------------------------
Date: Thu, 19 May 1994 10:18:15 GMT
From: ihnp4.ucsd.edu!newshub.sdsu.edu!nic-nac.CSU.net!usc!cs.utexas.edu!csc.ti.com!tilde.csc.ti.com!cauldron!ra.csc.ti.com!fstop.csc.ti.com!sbrown@network.ucsd.edu
Subject: Using 50ohm Coax instead of 75ohm
To: ham-ant@ucsd.edu
In article <Cq1z08.7px@cup.hp.com> genem@cup.hp.com (Gene Marshall) writes:
> I would like to install an antenna here at work for standard commercial
> FM reception. This will require about 150 feet of cable and I have
> plenty of RG-58 available. Is there any way I can make use of this or
> should I purchase 75-ohm cable?
>
> The ARRL handbook shows a 50-ohm to 75-ohm Broadband Transformer for
> using 75-ohm in a 50-ohm station setup, and states it's good for
> 2..30MHz. Yet, later in the article they said they tested it on VHF.
>
> Do you think I can get away with a couple of these transformers? Or is
> RG-58 pretty much limited to frequencies below 55MHz?
The short answer is that you can probably get away with nothing at all.
The mismatch to a 75 ohm antenna is 1.5 to 1, a reasonably respectable
match.
There is more to the story if signal strength is a concern at all. My
handy dandy wire and cable book says that your 150 feet of RG-58 will
present a loss of about 6.9 db in the frequency range you are
interested in. This assumes RG-58 or RG-58B, not RG-58A or RG-58C
which have even higher loss.
The 75 ohm stuff is not much better - RG-59 = 5.1 db. I don't know
what your physical setup is, but, if the mechanical problems are not
insurmountable, you would probably be better off with ordinary twin
lead. I don't have the loss figures right in front of me, but the
loss is much less than the loss in coax.
If you live in a high signal strength area, just run the RG-58 and
go for it.
My $0.02 worth.
*********************************************
| Steve Brown, WD5HCY | |
| sbrown@charon.dseg.ti.com | Simplicate |
| wd5hcy@wd5hcy.ampr.org | and add |
| [44.28.0.61] | lightness. |
| wd5hcy@kf5mg.#dfw.tx.usa.na | |
*********************************************
------------------------------
Date: Fri, 20 May 1994 15:10:46 GMT
From: ihnp4.ucsd.edu!agate!howland.reston.ans.net!europa.eng.gtefsd.com!darwin.sura.net!gatekeeper.es.dupont.com!eplrx7!eplrx7.es.dupont.com!duncanfj@network.ucsd.edu
Subject: Why are there no amateur helix antennas?
To: ham-ant@ucsd.edu
gratclif@magnus.acs.ohio-state.edu (Gregory W. Ratcliff) writes:
>I've been tinkering around here building some loop yagis,
>some logs, and now just starting on a helix. After researching
>this a bit, I can't for the life of me fiqure out why this isn't the
>most popular vhf/uhf antenna for amateurs.
>Are there patent restrictions still?
>Anyway, I'm trying to start a thread about constructing a few nice helixes
>(or is that helixs).
>My comments.
>Linear polarizition seems easy, according to Kraus.
>Gain seems 90% of yagi per boom length.
>Gain seems 300% of yagi per man hour to build.
>Gain seems much more "friendly" to errors.
>Bandwidth is much greater.
>Matching seems like a no brainer.
>The real question seems to be comming up with a good mechanical arrangement
>to hold the antenna. A boom with spreaders seems like too much work. How
>about large diameter coil supported only on the top. Something like 1/4"
>aluminum wire would be nice.
>Email or post we can all learn something in the discussion.
I agree - the Helix makes sense to me intuitively as well. I started on a
10 foot boom with spreaders for 440Mhz, had intentions of getting it tuned
and ten adding a 2 meter helix around it on the same boom. I work a little
satilite and the idea of having them concentric was appealing. Anyway,
never go the 440 on the air - still on saw horses in the basement, and have
no idea what kind of coupling/interaction problems I was headed for.
An
>greg
>Gregory W. Ratcliff
>Columbus, Ohio ICBM
>In the Air N1697X
>On the Air NZ8R
------------------------------
Date: Fri, 20 May 1994 15:55:15 GMT
From: pa.dec.com!src.dec.com!crl.dec.com!nntpd.lkg.dec.com!nntpd2.cxo.dec.com!iamu.chi.dec.com!little@decwrl.dec.com
Subject: Why are there no amateur helix antennas?
To: ham-ant@ucsd.edu
In article <gratclif.52.2DDC49F8@magnus.acs.ohio-state.edu>, gratclif@magnus.acs.ohio-state.edu (Gregory W. Ratcliff) writes:
|>I've been tinkering around here building some loop yagis,
|>some logs, and now just starting on a helix. After researching
|>this a bit, I can't for the life of me fiqure out why this isn't the
|>most popular vhf/uhf antenna for amateurs.
Because of the reasons you give below.
|>
|>Are there patent restrictions still?
|>
|>Anyway, I'm trying to start a thread about constructing a few nice helixes
|>(or is that helixs).
It's helicals (helices?) I think.
|>
|>My comments.
|>
|>Linear polarizition seems easy, according to Kraus.
|>Gain seems 90% of yagi per boom length.
Only if you consider circularly polarized antennas at both end. Otherwise
you have a 3 dB loss in gain when communicating with a linearly polarized
station.
|>Gain seems 300% of yagi per man hour to build.
|>Gain seems much more "friendly" to errors.
|>Bandwidth is much greater.
|>Matching seems like a no brainer.
True, but in weak signal work (where much of the antenna design effort goes)
pattern and gain are probably the most important issues. I'd rather spend
more time building an antenna with a good pattern and high gain, then spend
less time building a poorer antenna. Also, the problems associated with
matching are pretty well understood, so that shouldn't impose too great a
problem. And bandwidth for the amateur VHF/UHF bands isn't typically a
big issue as there is a tendency to use different antennas (with different
orientation) in different portions of the bands. So a vertically polarized
antenna on 70 cm only needs to span a third of the band. Likewise a
horizontally polarized antenna only needs to span an even smaller portion
of the band.
|>The real question seems to be comming up with a good mechanical arrangement
|>to hold the antenna. A boom with spreaders seems like too much work. How
|>about large diameter coil supported only on the top. Something like 1/4"
|>aluminum wire would be nice.
Exactly. The mechanical aspects for VHF are a pain. A 1 wavelength
reflector for 2 meters is a sizable reflector that will catch a lot of
wind. At UHF and microwave frequencies, the mechanical aspects get better,
although building and supporting a 12-15 turn 70cm helix is still a
non-trivial task.
Please don't construe this to suggest that folks not build helicals, but as
an explanation as to why they aren't the "universal antenna". I've built
a couple myself and had fun doing it. Certainly for circularly polarized
signals on the UHF bands, they're an attractive alternative to crossed
yagis.
73,
Todd
N9MWB
------------------------------
Date: 19 May 1994 20:32:08 GMT
From: ihnp4.ucsd.edu!newshub.sdsu.edu!nic-nac.CSU.net!usc!math.ohio-state.edu!howland.reston.ans.net!vixen.cso.uiuc.edu!usenet@network.ucsd.edu
To: ham-ant@ucsd.edu
References <hawley.769358693@aries>, <2rgdl5$kfd@news.CCIT.Arizona.EDU>, <hawley.769377021@aries>
Reply-To : ignacy@uiuc.edu (Ignacy Misztal)
Subject : Re: Ladder Line
In <hawley.769377021@aries>, hawley@aries.scs.uiuc.edu (Chuck Hawley) writes:
>Oh...300ohm. Well they have 450 in solid and stranded, 18 and 16 ga
>respectively. They also have 300 ohm KW twinlead. But who cares?
>So does Wireman. I like 'em both...
...............
Does any variety that you list have good insulation so that the cable
can touch gutters without side effects other than capacitive coupling?
I known that TV cables are manufactured with thin and thick
insulation.
Ignacy Misztal Ham radio: NO9E, SP8FWB
E-mail: ignacy@uiuc.edu
University Of Illinois 1207 W. Gregory Dr., Urbana, IL 61801, USA
tel. (217) 244-3164 Fax: (217) 333-8286
------------------------------
End of Ham-Ant Digest V94 #151
******************************