QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/antenna/940113.txt

Internet Message Format | 1994-11-13 | 14KB

Date: Wed, 20 Apr 94 04:30:08 PDT
From: Ham-Ant Mailing List and Newsgroup <[e-mail]>
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Subject: Ham-Ant Digest V94 #113
To: Ham-Ant


Ham-Ant Digest              Wed, 20 Apr 94       Volume 94 : Issue  113

Today's Topics:
                         70cm Parabolic Dish
                   ? About 5/8ths antenna at 900Mhz
Formula for determining optimum distance between elements in a Yagi beam
             GAP verses Butternut Comparison Questions..
                   Is that all there is to a G5RV?
           Satellite Receive Dishes Combined in Phase Array
                        Slot antennas on cars?

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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: 19 Apr 1994 19:01:15 GMT
From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!EU.net!sunic!news.funet.fi!nntp.hut.fi!vipunen.hut.fi![e-mail]
Subject: 70cm Parabolic Dish
To: [e-mail]

In article <[e-mail]> [e-mail] (John Boudreau)
VE8EV writes:
>Is it worthwhile to try to use a 2.5m parabolic dish for 70cm?
>It would be used for 70cm EME and also for satellite work.

With a good feed you would get about 18.9 dBi gain. In practice this is very
hard to accomplish due to considerable blocking. A 2.5m dish is simply too
small on 70cm to be a good choice. The gain would be good enough for satellite
work but not for EME. Even with a kilowatt you would be able work only a couple
of big guys. A single yagi with 5m boom would do the same job.

A better choice would be to use it on 23cm or above. With a good system
(feed, preamp, PA etc) you would have a "marginal EME station" capable of
tens of QSOs on 23cm.

Jukka OH6DD

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Date: 19 Apr 1994 16:10:31 GMT
From: ihnp4.ucsd.edu!swrinde!cs.utexas.edu!math.ohio-state.edu!magnus.acs.ohio-state.edu!csn!col.hp.com!news.dtc.hp.com!hpscit.sc.hp.com![e-mail]
Subject: ? About 5/8ths antenna at 900Mhz
To: [e-mail]

In article <[e-mail]>,
Eleen N. Kamas <[e-mail]> wrote:
>
>    !
>    |---> radiator
>    |
>    {---> mysterious loading coil
>    }
>    |
>    L--->coax 50 ohm

I believe the "coil" is a 180 degree phasing section
with a total wire length (not coil length) of 1/2 wave.
Works like a 1/4 wave stub (which also has a 1/2 wave
of wire).

Rick N6RK
[e-mail]

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Date: Tue, 19 Apr 1994 16:35:19 GMT
From: ihnp4.ucsd.edu!swrinde!cs.utexas.edu!math.ohio-state.edu!magnus.acs.ohio-state.edu!csn!col.hp.com!fc.hp.com![e-mail]
Subject: Formula for determining optimum distance between elements in a Yagi beam
To: [e-mail]

In article <[e-mail]> [e-mail]  writes:
: >Is there a formula for determining the optimum distances between the driven
: >element and the parasitic elements in a yagi beam?
: >
: >I know the driven element should be a 1/2 wavelength and the reflector 5%
: >longer and the director 5% shorter in a 3 element beam.  How do I determine
: >the distance between the driven element and the parasitic elements?  What
: >about if the yagi has more than 3 elements, say 7?
:

Joe Mack ([e-mail]) wrote:
:     Calculating the spacing between elements is like the multi body
: problem and there aren't analytic solutions (that I know of). Satisfactory
: answer have only become available since the advent of computers. It is only in
: the last 5 years or so (as far as I know) that people could answer
: with confidence what the max gain for a yagi of a particular lenght should be.
:
:     The only answers to your questions come from computers, either you
: look up tables of designs by people who know what they are doing, or you
: buy one of these programs and do it yourself. For yagis I recommend yagiopt
: (look in QST, I have no finacial interest in this program), which is
: about $100, or NEC, which is free but very difficult to use, or to get your
: feet wet, look for mininec, of which there are public domain versions,
: or try yagimax (about $25, again I have no financial interest in this program)
: which doesn't have the features of yagiopt, but which is cheaper.
:     good luck
:     Joe Mack NA3T
:     [e-mail]

If you make a three element yagi as described in the first paragraph it
will likely work OK. Using spacings of .1 to .2 wavelength should make
a usable yagi. Rough calculations like that will probably get you maybe
75% of maximum gain (for a given boomlength) and who knows how much
front-to-back/pattern. But if you want a 'quick and dirty' antenna with
some decent gain if should work OK. You could make the boom longer and
add some directors that are sightly shorter than the 1st director and
improve the gain.

Another possibility is to find a proven design, in a book or article, that
is to your liking and use that design.

As Joe mentioned above a good way to improve design is computer programs.
Yagimax is a nice program and is available from several ftp sites. You
can change spacings, elements lengths, element sizes and see the effect
it has on yagi performance. For pure yagi design I like YagiOptimizer (YO)
that Joe mentioned. You can tell the program how you want the yagi to
perform (peak the forward gain, peak F/B, or somewhere in between) and it
will optimize the design for those parameters. But at $100 it isn't cheap.
There are also other programs available that will model wire antennas as
well as the yagi.

So it all depends on how much effort you want to make. If you want to build
a yagi that will perform well it isn't too difficult. If you want to really
tweak and optimize a yagi a bit more effort is involved.

73, Jay K0GU                   [e-mail]

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

Date: 19 Apr 1994 11:14:14 -0400
From: library.ucla.edu!europa.eng.gtefsd.com!howland.reston.ans.net!news.intercon.com!panix!ddsw1!news.kei.com!hookup!news2.sprintlink.net!news.sprintlink.net![e-mail]
Subject: GAP verses Butternut Comparison Questions..
To: [e-mail]

In article <[e-mail]>,  <[e-mail]> wrote:
>results are well worth it.  The Butternut HF2V is great on 40 and decent on
>80, but the GAP just blows it away.  I worked DXCC on 80 and 40 with the
>GAP, running 100w or less, in a matter of a couple months of very casual
>operating.  Also, I had no trouble working anything I could hear on 80 and
>40.  It's so-so on 160, but I still managed to work DX with it.  If you
>have the room to put it up and the people to help you put it up, go for it.
>
>73, Mike KB3RG/CU3LF/CU0WPX

Mike,
Can you tell us more about your DXCC with the Gap. Did you work the
DXCC at the CU3LF and CU0WPX QTHs or at you KB3RG QTH?
Also if from KB3RG what were your most exotic and most distant QSOs?

Congratulations on the 80m DXCC with 100 watts (or was that DXCC combining
80 and 40m). 80m is tough with 100w and any antenna because the DX
station often has lots of local QRM on his end.


Mike Wood            Internet: [e-mail]
The Signal Group     Amateur Radio: NT4O
P.O. Box 1979     ***Avoid company disclaimers by owning the company ***
Wake Forest, NC 27588

Phone: [phone]       Fax: [phone]

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

Date: Tue, 19 Apr 1994 15:16:14 GMT
From: world![e-mail]
Subject: Is that all there is to a G5RV?
To: [e-mail]

In article <2okbac$[e-mail]> [e-mail] (Cecil A. Moore -FT-~) writes:
>Daniel T Senie ([e-mail]) wrote:
>
>: You've said this before. Did G5RV himself really say that RG58 was
>: required? Seems to me that ANY 50 ohm coax could be connected in with
>: only one real difference between them, line loss...
>
>Hi again, Daniel. I guess I didn't make myself clear. What Varney, G5RV,
>said in his latest writings is to eliminate the coax and bring the
>ladder-line directly to a balanced antenna tuner. Most of the commercially
>available G5RVs that I have seen use RG58 so that's why I pick on it.

The commercially available G5RV's I've seen use a PL-259 at the bottom
of the twin-lead, and let the purchaser add whatever coax they want. We
were working from different points of reference, so now I understand the
confusion :-).

>Obviously, the lower the transmission line loss, the better but 9913 at
>50 cents/ft has more than double the loss of ladder-line at 10 cents/ft.

Of course the 50 ohm coax plugs into a rig with an auto tuner, and the auto
tuners in the various newer rigs will handle a G5RV on all bands 160-10.

While use of such a tuner is not necessarily optimal, nor is the use of
coax in this setup, I find that a G5RV and a small rig with an auto tuner
(eg. FT890) makes an excellent emergency station. It also makes a very good
first station for a new ham.

I know you're a strong proponent of ladder line. I like the stuff too, but as
long as one understands loss factors of different feedlines, and such, the
use of coax is often much more convenient. The extra expense of coax is often
worth it given the added benefits of routing, burying, and connecting options
gained.

--
---------------------------------------------------------------
Daniel Senie                 Internet:     [e-mail]
Daniel Senie Consulting                    [e-mail]
508-779-0439                 Compuserve:   74176,1347

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

Date: Tue, 19 Apr 1994 11:59:47 GMT
From: ncar!csn!boulder!cnsnews!spot.Colorado.EDU![e-mail]
Subject: Satellite Receive Dishes Combined in Phase Array
To: [e-mail]

In article <[e-mail]>,
Alan Anderson <[e-mail]> wrote:
>>In <[e-mail]>, [e-mail] (Richard W Weening):
>>>
>>>Is anyone aware of successful methods for combining two or more satellite
>>>receive dishes in phase array as a means of achieving receive gain
>>>comparable to a single larger dish?                           ^^^^
>>
>>I've always seen phased antenna arrays used for more precise pointing, not
>>for increased gain.  Of course, with a narrower "beam" you GET more gain,
>>so maybe it isn't as unusual an idea as it first seemed....
>>
phased array antennas are commonly used to acheive gain.

In article <[e-mail]>, Joe Mack <[e-mail]> wrote:
>       COmbinng antennas into arrays is covered in most texts on antennas. You
>will have to do it at receive frequency and feed the power to a combiner. The
>pointing accuracy needed will be approx that for an antenna with the diam=
>spacing between the two dishes (ie you'll need to be very accurate), while
>the signal will only go up 3bd. This is great for radia astronomy where you
>want to know exactly where your source is. However you just want more
>signal, in which case it will be easier to buy a bigger dish.
>

You don't have to point the individual antennas in an array any better than
you would have to point them by them selves.  You do have to match the line
lengths from the antennas to the power combiner at the higher pointing
accuracy, but this is relatively easy.  In fact with a variable line length
you can steer the combined beam anywhere within the main beam of the
single dish.

You don't have to combine the signals at the carrier frequency either, if
the two downconverters are driven by the same local oscilator.
A high frequency power combiner might be cheap than two down converters.

Whether a big dish is easier than a few small dishes, depends on whether
you are more adept at mechanics or electronics, and how often you need
to reposition your dish.

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

Date: Tue, 19 Apr 1994 19:12:41 GMT
From: ihnp4.ucsd.edu!usc!elroy.jpl.nasa.gov!ncar!csn!col.hp.com!srgenprp![e-mail]
Subject: Slot antennas on cars?
To: [e-mail]

Tom Bruhns ([e-mail]) wrote:
: Has anyone out there experimented with slot antennas on cars?  There are
: several places you could make this work, but I was thinking of a slot
: formed from wire (or copper tape) placed at the top inside of the rear
: window.  If anyone has experimented with this, I'd be interested in
: the results:  impressions about performance transmitting and receiving,
: amount of RF in the passenger compartment, problems feeding the
: antenna, ...   It seems like the dimensions are right for this to work
: as a "stealth" antenna on 2m and 440MHz, with vertical polarization.

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.

AL N1AL

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End of Ham-Ant Digest V94 #113
******************************