QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/antenna/940362.txt

Internet Message Format | 1994-11-13 | 17KB

Date: Tue,  1 Nov 94 04:30:26 PST
From: Ham-Ant Mailing List and Newsgroup <[e-mail]>
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Subject: Ham-Ant Digest V94 #362
To: Ham-Ant


Ham-Ant Digest              Tue,  1 Nov 94       Volume 94 : Issue  362

Today's Topics:
                    2 meter HT on Snowmobile help!
                        50 Ohms Why ? (2 msgs)
                      Best vertical - Butternut?
                BNC vs N vs UHF at VHF/UHF frequencies
                        HARDLINE...which one!?
                 Wanted! Measurements for 220 J-Pole
                What's a good antenna for a Dorm Room?
                        x-beam vs yagi, ELNEC

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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: 1 Nov 94 14:45:51 GMT
From: [e-mail] (Bud Kuenzli)
Subject: 2 meter HT on Snowmobile help!

   Okay, here is the plan....my wife and I are buying a Kenwood 22AT 2
meter for communication between us and for emergency use while we are
snowmobiling. While we are riding in the area and talking back and forth
(we live in North Pole Alaska) the rubber ducky will be just fine, but
there may be a time when we need to hit a repeater at a distance so I am
trying to learn what antenna I might add to extend my range. Would a simple
1/2 wave telescoping antenna be as good as anything we might add to the
snowmobile itself? If I was to add an antenna to the snowmobile it would
either have to be strong or flexible enough so that it would "bend with the
wind" when we pass under a tree branch, or it would need some kind of
flexible attachment, or both. It might be something that we could extend,
leaving it "folded" in normal use. I have thought about a 1/2 dipole but we
could be on the tundra with no tree to hang it between...
        As I said, for daily transmission we are find, but if I drive off a
glacier, I'd like my wife to get that added ooomph of a better antenna. I
have an electric start machine so I'll rig my hand held to run off the 12
volt battery eventually. I'd imagine I could rig my wife's to run off her
alternator....??  Any ideas with regard to type and attachment of other
antennas or schemes to increase our range would be appreciated. Thanks in
advance!


                                  \
                                   \
                                  / \_
      /----\                    /      \
     /      ///////////////////         \
   /                                     \_
/                Bud Kuenzli                \
/                North Pole, Alaska         /
/                                          /
/______////////////////////////___________/     /
          @________________@       ____|_______/

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

Date: 31 Oct 1994 08:39:51 -0800
From: [e-mail] (Ron Cole)
Subject: 50 Ohms Why ?

Alastair "J." Downs ([e-mail]) wrote:
: This has probably been asked before (but at least it may have been clarified)

: Why choose 50 ohms as the stanard characteristic impedance for RF kit ?

Here's how it was explained to me.  Back many years ago standard sizes of
copper water pipe were used to make coax.  A combination of two sizes.
Inner and outher conductors yeilded a 51 ohm impeadnace.  That be default
becam the impeadnace used.  No how the 300 or 450 ohm open lines od even
some of the comercial stuff like 270 ohm open line.

I know their has to be a better explination but thats what an Old Radio
engineer told me.  Hey we was building 50Kw AM's  over 60 years ago so
how am I to argue.

----------------------------------------------------------------------
Ron Cole                   Internet:[e-mail]    ICBM:29 31.03 N
N5HYH                      CIS:70325,102                   98 25.55 W
CE KZEP/KHBL               AX25:N5HYH @ K3WGF.STX.NA
----------------------------------------------------------------------

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

Date: Fri, 28 Oct 1994 22:38:19 GMT
From: [e-mail] (Tom Bruhns)
Subject: 50 Ohms Why ?

Bob Hale ([e-mail]) wrote:
: In article <[e-mail]>, Joe Mack <[e-mail]> wrote:
: >In article <[e-mail]> [e-mail] (Alastair "J." Downs) writes:
: >>Why choose 50 ohms as the stanard characteristic impedance for RF kit ?
: >
: >It's a compromise. The minimum attenuation occurs at 70ohms (which is
: >presumably why cable TV companies here use 70ohm cable), the maximum
: >power handling is at (I think) 37ohms and so 50ohms is about in the
: >middle.

: Correct.  But the coax which produces these results is air-dielectric
: copper coax, not the plastic insulated stuff that most of us use.  If
: you try to find the minimum loss or maximum power handling impedances
: for plastic insulated coax you will find that you need to know the
: operating frequency because the dielectric's behavior changes so much
: with frequency.

Fred Terman published in "Radio Engineers' Handbook" a pretty early
discussion of this.  For frequencies below about 1GHz, the dielectric
loss is negligible, but insulation causes you to have to use a smaller
inner conductor for a given outer conductor and impedance, and therefore
you get higher losses-- but the ratio of inner conductor diameter to outer
conductor diameter remains constant for the minimum loss configuration.
The result is about 77 ohms for air insulation, down to about 51 ohms for
solid polyethelene dielectric.  Solid Teflon is just a bit higher, about 52
ohms as I recall.  Foam is between the two; in fact, it will be 77 times
the propagation factor (velocity factor) for the line.   Also, if the inner
and outer conductors are different materials, then the min occurs at a
different diameter ratio; someone suggested that aluminum-jacketed
foam-insulated line with a copper center conductor likely is min loss near
a 75 ohm configuration.

Quoting from Terman about max power:

"The power that can be transmitted for a given maximum voltage gradient in
a concentric line [coax] having an outer conductor diameter D is a maximum
when D/d = 1.65, corresponding to Zo = 30 ohms."

I'd note that this is for air-insulated line, and if the dielectric is
uniform, the same D/d should hold for other dielectrics.  I'd also note that
for CW operation at HF and above with a 1:1 SWR, you will probably reach the
_thermal_ limit for the line long before you reach the _voltage_ limit.
RG-213/U is rated at 5000 volts, and that would be half a million watts at
50 ohms.  You'd melt the line in short order at that power.  It's a useful
rating for _pulse_ applications, but not for CW.  (Let's see, if you had
5MW, 1dB/100ft, that would be 100kW/100 feet or 1000 watts per
foot...No, I don't want to be close by when you try that one!)

In any event, the min attenuation thing is a rather broad minimum.  I think
the answer really comes down to "a lot of practical loads like resonant
antennas are in the vicinity of 50 ohm loads, and the dimensions of the
line are practical."  Some engineers quite a while ago made an engineering
choice which has been good enough that there hasn't been any serious effort
to change it.  In fact, the 75 ohm standard for TV and video stuff might be
more interesting.  Someone apparently saw fit to buck the 50 ohm standard
on that.  Anything to do with the ease of going from a 300 ohm folded
dipole to 75 ohms with a balun?

73, K7ITM

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

Date: 31 Oct 1994 16:19:41 GMT
From: [e-mail] (Ignacy Misztal)
Subject: Best vertical - Butternut?

I am in a process of selecting a vertical.  My 2x40ft dipole at 25ft
fed by a ladderline works all band with a tuner but performance isn't
good except on 40m.

I would prefer a vertical with a 10-40m coverage, 80m being a bonus.
Since there is some room for radials, I don't consider expensive R7
particularly because of its narrow bandwidth on 20 and 40m.

One of the choices is Butternut HF6V.  It is light, its mass is
concentrated in the lower section so as to present a low windload, and
its coils are large.  Did anybody compare HF6V to any other vertical
(or anything else)?  Can anyone recommend anything else

One choice of a home made vertical could be a dipole with one part
being a verical pole and the other part horizontal (or sloping). It
could be multiband too. Anybosy tried to do it? perhaps one problem
with it would be a lack of symmetry.

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: Sun, 30 Oct 1994 00:22:50 GMT
From: [e-mail] (Alan Bloom)
Subject: BNC vs N vs UHF at VHF/UHF frequencies

Jeff DePolo ([e-mail]) wrote:
..
: All of the tests were done on the 440 MHz band.  ...

: I fould that the patch cables that used either N or BNC connectors,
: including the one BNC right-angle connector, had no measurable effect on
: loss or SWR at 440 MHz.  ...

: The UHF connectors are another story.  With the Amphenol phenolic
: UHF connector in place, SWR was calculated at 1.46:1, and the
: *measured* loss was approximately 0.3 dB.  Note that the measured loss
: value doesn't match what the calculated loss should be (see the
: last paragraph as to why).

If the insertion loss were from reflection (impedance mismatch) only,
then the loss would be .16 dB.  Evidently the phenolic not only upsets
the 50-ohm match but also absorbs some of the power.  Interesting.

: So what did I learn from all of this?  Well, nothing new really.
: It reaffirmed the age-old caveat to stay away from UHF
: connectors on VHF/UHF frequencies.

Not sure I agree about the VHF part.  The worst connector you could find
lost only .3 dB at 450 MHz.  I bet it wouldn't be more than .1 dB on the
two meter band, which I think most hams would find acceptable.  And
good-quality connectors do better than that.

AL N1AL

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

Date: Mon, 31 Oct 1994 07:33:28 -0500 (EST)
From: Mike Fletcher <[e-mail]>
Subject: HARDLINE...which one!?

On 30 Oct 1994, David M. Roseman wrote:

> ok, now i know there are TWO types of hardline coax...
> basic CATV stuff, and radio stuff.
> but can i use the CATV type with out any major drawbacks?
> cause it's easier to get FREE, CATV then radio type...so...
> which is it!?
>
>
>
> thanks
>
> DAvid
> |-----------------------------------------------------------------------|
> |         David Roseman       |          [e-mail]                |
> |      SysOp of NODE 3 BBS    |          The Flying HAm - BBS           |
> |     Running OBV/2 Software  |          KBR-9318 - CB                  |
> |                             |          N3SQE/SVARC - Ham              |
> |         HAmmy in IRC        |  [e-mail] - Packet  |
> |-----------------------------------------------------------------------|
>
>
David,
    If you are discussing the commercial CATV cable types ie.  the
distribution cable that they hang on poles etc. which is generally 1/2 to
3/4 inch diameter cable with a solid aluminum sheath and a center
conductor surronded by foam, then you have no problem.  A couple of
people make coupling transformers to use the 75 ohm CATV cable with 50
ohm Radio systems. I don't have a name handy but check QST, CQ etc, or
the local hamfest and you can probably find them.  If you were discussing
small indoor 75 ohm cable I dont think the cost of the couplers would be
worth it, probably cheaper to buy RG58..  Hope this helps...

73 De AD4HV   Mike Fletcher
[e-mail]

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

Date: Mon, 31 Oct 1994 01:39:19 -0700
From: [e-mail] (Jim Fitzharris)
Subject: Wanted! Measurements for 220 J-Pole

  Does anyone out there have the measurements, formula, or plans for
building a 220Mhz J-pole? Any info. would be greatly appreciated.
                                                            Thank you for your time.
73's
Sean  KE6MOW

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

Date: Sun, 30 Oct 1994 15:55:00 GMT
From: [e-mail] (Clint Bradford)
Subject: What's a good antenna for a Dorm Room?

C>Path: planet!isdnlin.mtsu.edu!darwin.sura.net!math.ohio-state.edu!news3.acns.
 >From: [e-mail] (CHARLES R. MATTHEW)
 >Newsgroups: rec.radio.amateur.antenna
 >Subject: What's a good antenna for a Dorm Room?

C>     Charlie N0FXD here, Looking for sugjestions of antennas types that
 >would work good in a college dorm room (we like to call it a residence
 >hall). I work on 2m FM/Packet and 10 SSB/CW. All replys welcome!

2M J-Poles are easy, cheap, and they WORK!!!


     === 2m/70cm Dual Band J-Pole made from 300 ohm twin lead ===

              _____      _______       ___
                |       |       |       |
                |       |   O   |       |
                |       |       |       |
                |       |       |       |
                |       |       |       |
                |       |       |       |
                |       |       |       |
                |       |       |       |
                |       |       |       |
                |       |       |       |
                |       |       |       |
                |       |       |       |
                |       |       |       |
                |       |       |       |
             54-1/4"    |       |    38-1/2"
                |       |       |       |
                |       |       |       |
                |       |       |       |
                |       |      _|       |
                |       |   N |_       _|__
                |       |       |       |
                |       |       |       |
                |       |       |       |
                |       |       |       |
                |       |       |    15-3/4"
                |       |       |       |
                |       |_______| ___   |
                |       |       | 1/4"  |
               _|_      |       | ___  _|__
                        ^       ^
                        |       |
                    Coax Inner  Coax Outer
                    Conductor   Conductor


         SWR is 2:1 across the 2m band and from 435mhz to
                     450mhz on the 70cm band.


1.  Use good quality TV twin lead.
2.  Strip insulation at the solder point for coax feedline.
3.  Cut out and remove the 1/2" long notch N.
4.  Feed with a length of 50 ohm coax and terminate with the
    appropriate connector.  Tape coax at feedpoint to the twin lead,
    or use heat shrink, and make sure the joints are insulated from
    each other.
5.  Antenna may be sleeved inside 1/2" PVC for outside mounting or
    hung on a loop of string run thru hole O.

---
 * QMPro 1.53 * Thesaurus: ancient reptile with an excellent vocabulary.

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

Date: 31 Oct 94 16:58:06 GMT
From: [e-mail] (Christie Harper)
Subject: x-beam vs yagi, ELNEC

I am looking a building a small antenna for 29.39 Mhz (RS-10 downlink) and
was doing a little modeling withe ELNEC comparing a 2 element yagi vs an
X-Beam antenna.  Not having any practical experience with X-beams I was
wondering if anyone knew what the pattern should look like and what kind
of performance w.r.t a 2 element yagi should be.  According to ELNEC I
think I will go with the 2 element yagi.

Is there any interest in this group of posting to a common site
(any suggestions) ELNEC input files?

Has anyone written or would be interested in tools to generate ELNEC
input files for some standard types of antennas (K1FO yagis, Quads,...)?

end
        the views expressed here are the author's

C. Harper         [e-mail] or [e-mail]
KD4QIO
SPARTA Inc         [phone] x1216 voicemail
4901 Corporate Drive     [phone]       FAX
Huntsville AL 35805
"we have met the enemy and he is us."  w. kelly

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

End of Ham-Ant Digest V94 #362
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