QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/antenna/940136.txt

Internet Message Format | 1994-11-13 | 24KB

Date: Mon,  9 May 94 04:30:14 PDT
From: Ham-Ant Mailing List and Newsgroup <[e-mail]>
Errors-To: [e-mail]
Reply-To: [e-mail]
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Subject: Ham-Ant Digest V94 #136
To: Ham-Ant


Ham-Ant Digest              Mon,  9 May 94       Volume 94 : Issue  136

Today's Topics:
                       2m 'Tenna for Apartment
                      Homebrew antenna questions
                             Loop Skywire
                               Mininec3
                       Mininec help file here!
               Noise in apartment antenna + 20 (2 msgs)

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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: 7 May 94 14:30:41 GMT
From: agate!usenet.ins.cwru.edu!ns.mcs.kent.edu!kira.cc.uakron.edu!malgudi.oar.net!hypnos!voxbox![e-mail]
Subject: 2m 'Tenna for Apartment
To: [e-mail]

-----BEGIN PGP SIGNED MESSAGE-----

[e-mail] (Jack Glazko) writes:

> When I was in college, I had a radio set up for HF bands using
> some (28 ga?) magnet wire and a tuner.  Did the job for what I wanted.  We
> set it up by doing a midnight installation to the roof across the
> courtyard in our dorm (insulated at end), and attaching the other end at
> my dorm room window.  Worked great for months, and it was up 4 stories.  The
> magnet wire was almost invisible, and I didn't have any problems until it
> was hit by a high-flying football.  The people on the ground never had
> any idea what they'd hit, and boy did they look surprised when the
> football took a sudden turn!

I did something similar in Garner House at UIUC in the fifties,
where my 2nd station call was K9HBV. My only problem was a guy
at the far end who spotted it and decided to hook a SWBC
receiver to it. Boy, did he get a helluva surprise the first
time I called CQ on 40 CW!


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+------------------------------------------------------------+
| Jim Grubs, W8GRT   Voxbox Enterprises   Tel.: [phone] |
|      I _DO_ speak for Voxbox; in fact, I _AM_ Voxbox       |
+------------------------------------------------------------+

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

Date: 9 May 94 02:38:33 GMT
From: ihnp4.ucsd.edu!usc!math.ohio-state.edu!cyber2.cyberstore.ca!nwnexus!ole!rwing!eskimo![e-mail]
Subject: Homebrew antenna questions
To: [e-mail]

In article <2q3uoa$[e-mail]>,
Cecil A. Moore -FT-~ <[e-mail]> wrote:
>Bruce Pea ([e-mail]) wrote:
>: I would encourage you all to wrap wire on pvc!!
>: 73 de Bruce, N9WKE
>
>Hi Bruce, I have a number of questions for you. What is the equivalent
>quarter-wavelength resonant frequency? Did you know that an 80m
quarter-
>wave vertical has a take-off angle of 50-60 degrees on 20m-10m? What is

>your SWR on your single feed-line? Are you going to replace the
feed-line
>with coax when you add your radials? High SWR on lengthy runs of coax
>equals significant losses.
>
>The take-off angle on a vertical antenna increases above 5/8 wavelength
>to the point of uselessness especially during the sunspot low. You
>probably have a useful 80m/40m antenna but I wouldn't expect much out
>of it on 20m-10m.
>
>I suspect the reason that it doesn't load on 17m and 12m is that you
>are trying to force power into something like 3000+j2000 like my 88 ft.
>center-fed dipole on 15m.
>
>Didn't mean to rain on your parade.
>
>73, KG7BK, [e-mail]


OOPS!  Cecil has fallen into a common trap (no pun intended).  Bruce's
antenna is only 10 feet long - no matter how much wire is wound into a
helical coil, it's only 10 feet from end to end.  The radiation pattern
is determined by the physical length of the antenna, period.  The
impedance, kind and type of loading coils, etc, etc, have nothing to do
with it.  Use Mininec, Elnec or any other antenna analysis program and
you can easily verify the above.  (Speaking only of single-element wire
antennas, of course).  With Bruce's antenna, the radiation pattern will
be essentially the same on 80-10 meters.  The efficiency, however is
open to question.  From much experience with mobile antennas, I would
guess that it will work pretty well on 40, 30 and 20, and a bit less
well on the other bands.  10 feet is just too short on 80, although you
will get out - your overall efficiency is going to be in the 5-10%
range.  If you could make it 30-40 feet high, you'd notice a dramatic
improvement.  On the bands above 20, you have too much coil and that
creates losses too.  Your antenna tuner will be working overtime to
compensate for too much of a good thing!  A better design would be to
only use as much coil as you need on those frequencies and not use the
antenna tuner at all.  Taps work fine, but of course you need some kind
of switching arrangement.  Even better than that would be to make two
separate antennas - one for 80-30 meters, having JUST enough coil to
resonate it on 80, and another for 20-10, likewise having JUST enough
coil to resonate it on 20.

I don't want to rain too much on your parade, Bruce, but if this really
were a good design, the antenna books would have it highly recommended.
They don't.  The laws of physics just get in the way.


73 es gl

Bill, W7LZP



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

Date: 8 May 94 14:55:43 -0600
From: ihnp4.ucsd.edu!sdd.hp.com!saimiri.primate.wisc.edu!news.doit.wisc.edu!uwec.edu!hemp![e-mail]
Subject: Loop Skywire
To: [e-mail]

Hello-
    Now that the weather in this part of the country is turning Very
Nice, and classes are about to end, what else can a young (married)
man's fancy turn to?  But of course, antennas!

    What I was wondering, does anyone have any comment on the loop
Skywire antenna that is in the Handbook?  It looks pretty good, and the
article claimes that it does well, but I would be interested in other
comments as well.

Thanks in advance-
    Mike White
    N9UXC/KT     [e-mail]

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

Date: Sun, 8 May 1994 22:52:16 GMT
From: ihnp4.ucsd.edu!agate!darkstar.UCSC.EDU!news.hal.COM!olivea!news.bu.edu!att-in!cbnewsm![e-mail]
Subject: Mininec3
To: [e-mail]

In article <[e-mail]> [e-mail] (Mark Hemlick Ph. D.) writes:
>Hi to all,
>
>Is the mininec3 _manual_ available at any FTP sites?  Please post site
>address if you know it,  Thanks in advance.
>
>73 Mark KA3LFG

The Mininec3 manual is NOT available at any FTP site. However there is a
help file that I created that will show you how to use it. It is on a FTP
site whose name escapes me right now. I have uploaded Mininec.zip to Genie
and the ARRL BBS 203-666-0578 that contains Mininec3 and the help doc. Also
I uploaded the help doc to Compuserve as Mininec.doc. This help doc will
take you step by step through the process of designing a dipole after that
you should be able to design other antennas. Also explains the X,Y,Z
coordinate system and the other ins and outs of Mininec. Hope this helps!

Jeff Jones
Ab6MB


--
 Jeff Jones  AB6MB         | Vote out those who voted for the North American
 [e-mail]   | Free Trade Agreement!
 Infolinc BBS 510-778-5929 |

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

Date: Sun, 8 May 1994 22:59:04 GMT
From: ihnp4.ucsd.edu!swrinde!cs.utexas.edu!convex!news.ssc.gov!fnnews.fnal.gov!att-in!cbnewsm![e-mail]
Subject: Mininec help file here!
To: [e-mail]

Oh what the heck, here is the Mininec help file!



Here is some help for new Mininec users who don't have the manual...

How Mininec works is by taking the antenna elements that you specify
and divides them into segments. It uses the individual segments to
calculate the total currents and voltages for your antenna. so the
more segments the better the accuracy but the longer it takes for
Mininec to calculate. Mininec will ask you for the number of wires your
antenna has. A dipole has 1 wire and a 3 element beam would have 3
wires, one each for the reflector, driven and director elements. Each
one of those wires will be broken up into the number of segments that
you specify. 10 is generally a good number to use.

All individual wires consist of X,Y,Z coordinates. Think of yourself
facing broadside to a dipole or where you are now standing the wire
being parallel to you. The X coordinate comes out of the dipole at
a 90 angle right at you. The Y coordinate goes from left to right or
corresponds to the length of the dipole. The Z coordinate is the height of
the dipole above ground. All measurements are in meters. (multiply feet
by .3048 to convert to meters).

As an example, take the following wire dipole;

Beginning of wire               End of wire
X       Y       Z               X       Y       Z
0       0       10              0       10.19   10

This would be a 20 meter dipole at 10 meters high. Easy right? Sure you say,
how did he do that? OK here is how you do it.

Let's start with the beginning of the antenna, in this case a dipole;

First what is X? Remember X is coming out at a 90 degree angle right at you.
A dipole has nothing that comes out at a 90 angle out at you so X is 0.

Second what is Y? Remember Y corresponds to the length of a dipole. So the
starting point of the length of a dipole is zero or Y = 0.

Thirdly what is Z? Remember Z corresponds to the height of a dipole. As this
end of the dipole is at 10 meters above ground, Z = 10.

Now for the end of the antenna. X is 0 as there is nothing coming out at us
at 90 degrees. Y is now the endpoint of the dipole and as this antenna is a
20 meters dipole Y = 10.19 (meters). Z is the height of the dipole at the
endpoint and as it is the same height above ground as the beginning of the
dipole Z = 10 (meters).

This is how the dipole looks to Mininec;

                          Length
                Y = 0                       Y = 10.19
                -----------------------------
                             /              |  H
                            /               |  e
                  X = 0    /                |  i  Z = 10
                          /                 |  g
                         /                  |  h
                        /                   |  t

Remember X is coming straight out of the side of the dipole at a 90 angle
right at you.

Now that you have your wire setup, the next step is the concept of
Segments. This is how Mininec breaks the wires up for it's computations.
10 segments is a good number to use to start with. Mininec computes
the currents and voltages in each segment and uses those results to
calculate the total efficiency and radiation patterns of your antenna.
The more segments the better the accuracy and the slower it's computations.

Source Pulses are where you feed your antenna at. If you have a dipole
divided up into 10 segments then to feed it in the middle you would
use segment 5. Basically a source pulse is nothing more then what segment
you feed your antenna at.

Let's use Mininec now to create a antenna model;

FREQUENCY (MHZ)?  Let's put 14 here.

ENVIRONMENT (+1 FOR FREE SPACE, -1 FOR GROUND PLANE)? Put -1 for real ground.

NUMBER OF MEDIA? Put 1 here

RELATIVE DIELECTRIC CONSTANT, CONDUCTIVITY? 13,.005 works well as this is about
average ground.

NO. OF WIRES? Put 1 here as we are modeling a dipole.

NO. OF SEGMENTS? Put 10 here as this a good number for modeling.

END ONE COORDINATES (X,Y,Z)? 0,0,10  (This is beginning end of the dipole
                                      and all numbers are in meters)

END TWO COORDINATES (X,Y,Z)? 0,10.19,10   This is the other end of the dipole
                                          and 10.19 is the length and 10 is
                                          height above ground. Both in meters.

                     RADIUS? .001  This the diameter of the wire in meters.

CHANGE WIRE NO. 1 (Y/N)?  If OK put N

  CHANGE GEOMETRY (Y/N)?  If OK put N

NO. OF SOURCES? Put 1 here. This tells the program how many sources of power
                            are being applied to your antenna. Ie.. coax

PULSE NO., VOLTAGE MAGNITUDE, PHASE (DEGREES)? 5,1,0  This tells Mininec where
to put the coax at. Remember the 10 pulses? Pulse number 5 is in the middle of
your antenna. Voltage is 1 volt and forget about the phase just put zero there.

NUMBER OF LOADS? 0  This is for traps, resistors, etc...

You will see a menu with various options. Choose P - COMPUTE FAR FIELD PATTERNS

It will now say BEGIN MATRIX FILL

Nex it will now print out something like this;

PULSE 5         VOLTAGE = ( 1, 0J )
                CURRENT = ( 9.728E-03, -48.54408 J )
              IMPEDANCE = ( 68.27696, -48.54408 J  )
                  POWER = 4.864229E-03 WATTS

CALCULATE PATTERN IN DBI OR VOLTS/METER (D/V)? Put D here for DBI. DBI
usually stands for DBs over a Isotropic Dipole. Substract 2-3 DBs to
get what it would be in the real world as a Isotropic dipole doesn't exist.
Dipoles are considered to have 2-3 DB gain over a Isotropic Dipolei.

Now Mininec will ask you for ZENITH angles. The Zenith goes from 0 degrees
straight up to the sky swings directly out to the horizon and then to 180
degrees below the antenna all at right angles to the antenna. This corresponds
to broadside radiation. Still not clear? Think like this, face the horizon,
put your hand straight up, this is 0 degrees straight up. Okay, now point your
hand at the horizon, this is a zenith angle of 90 degrees. Point your hand
at the ground, this is a zenith angle of 180 degrees. Now here is how Mininec
likes to see it. Put in 0 (starting angle),10 (how many degrees to increment),
10, (how many times to increment). This works out to start out at 0 degrees
pointing straight up and increment 10 degrees towards the horizon 10 times.
Or goes from 0 degrees and steps 10 degrees at a time until it reaches 90 deg.
At 0 and each 10 degrees Mininec will calculate the strength of the radiation
pattern in DB's. Also 90,-10,10 will also work. This starts at 90 degrees
straight off the side and works back up to 0 degrees. This is exactly the
same as 0,10,10 only it does it backwards. Also you can use even smaller
increments like 0,5,20. This will calculate at every 5 degrees from 0 to
90 degrees. What ZENITH really does is calculate the radiation angles
off the side of your antenna. So when Mininec asks the following;

ZENITH ANGLE : INITIAL, INCREMENT, NUMBER? Put in 0,10,10.

Now Mininec will ask you for the Azimuth angles. 0 degrees corresponds to
pointing straight out towards the horizon at 90 degrees from the center of the
dipole. Imagine you are standing facing the horizon. If you point your hand
straight out towards the horizon this is Azimuth angle of 0 degrees. Now keep
it out and move it sideways 10 degrees to your left. This a Azimuth angle of
10 degrees. If you had moved it to your right this would have been a Azimuth
angle of -10 degrees. What the Azimuth angle is really good for is seeing
if there is cloverleaf pattern off the broadside of your dipole or for seeing
the amount of front, side and back radiation on Yagi antennas. As we are
not interested in this at this time do the following;

AZIMUTH ANGLE : INITIAL, INCREMENT, NUMBER? Put in 0,0,0

FILE PATTERN (Y/N)? Put N or this will save the results into a file and you
                    will have to view the file to see the results.

Mininec will now calculate the Far Field pattern for you. You will see
5 columns named respectively; ZENITH ANGLE, AZIMUTH ANGLE, VERTICAL PATTERN (DB)
HORIZONTAL PATTERN (DB), TOTAL PATTERN (DB). Under the columns with the
(DB) after their names is the calculated amount of power in DB's your antenna
is putting out. The TOTAL PATTERN is what you want to look at. This is the
power output in DB's that your antenna is calculated to be radiating and has
the most useful figures. Due to the way the Mininec calculates using the
ZENITH ANGLE and numbers of 0,10,10 it will be backwards compared to
published antenna radiation pattern charts. 90 degrees is actually 0 degrees
and 80 is 10, 70 is 20, etc... on antenna radiation pattern charts. You can
either just convert it in your head or do put 90,-10,10 instead of  0,10,10.
Then is will correspond to antenna radiation charts.

For some more good information and help get a copy of the 1991 February QST
article called "MININEC: The Other Edge of The Sword".
Also get Volume 3 of "The ARRL Antenna Compendium" as there is a great
article called "Modeling HF Antennas with MININEC" that is really helpful.
These 2 resources will really deepen your understanding of Mininec!

Here's some good figures for RELATIVE DIELECTRIC CONSTANT and CONDUCTIVITY
for ground;

    20,.03      Very good ground        Rich soil
    14,.01      Good ground             Rich soil
    13, .005    Average ground          Heavy clay soil
 12-14, .002    Poor Ground             Cities, Industrial Areas
     5, .001    Very poor ground        Cities, Industrial Areas, High building.


Also here is some more good information that will make your life simplier
when designing a antenna on Mininec. Rather then inputing the wires and
segments manually each time use MNPRE.EXE that comes with Mininec. First
create a file called XXXX.NEC that has the following format;

GW,,pulses,X1,Y1,Z1,X2,Y2,Z2,diameter.

Using a text editor let's make a file called 20METER.NEC that looks like this;

GW,,10,0,0,10,0,10.19,10,.001

Run MNPRE and it will ask you for a file called XXX.NEC. Just put in
20METER.NEC. It will create a file called MININEC.INP and as long as
it is in the same directory as Mininec it will use data from MININEC.INP
to create the wire portion of the antenna.


If you have any more questions send email to me here or to
[e-mail]. The address in my .sig is not good
any more. 8-)

Jeff
--
 Jeff Jones  AB6MB         | Vote out those who voted for the North American
 [e-mail]   | Free Trade Agreement!
 Infolinc BBS 510-778-5929 |

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

Date: 8 May 94 14:33:45 GMT
From: [e-mail]
Subject: Noise in apartment antenna + 20
To: [e-mail]

While awaiting my license, I bought an Icom 720 A and tried stringing
up a simple horizontal dipole.  I am getting +20 static whenever I rig
up the antenna.  I'm using speaker wire for the antenna and speaker
wire for the ground.  Unhooking the ground seems to do nothing at all.
Any antenna I rig up seems to just bring on the noise.  Unfortunately,
I'm new at this so all serious suggestions wil be accepted. BTW, of
course my apartment has a no antenna policy and I am on the first floor.


My new HTX 202 handie talkie seems to receive fine.  An old Zenith shortwave
radio picked up some stuff, real bad at times but I could usually find
WWV.  I took the Icom over to a friend's house last night and on his
antenna he got Mexico and Alabama just fine.

[e-mail]

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

Date: 9 May 94 03:12:51 GMT
From: ihnp4.ucsd.edu!usc!math.ohio-state.edu!cyber2.cyberstore.ca!nwnexus!ole!rwing!eskimo![e-mail]
Subject: Noise in apartment antenna + 20
To: [e-mail]

In article <[e-mail]>,
Dave van De Kerk <[e-mail]> wrote:
>While awaiting my license, I bought an Icom 720 A and tried stringing
>up a simple horizontal dipole.  I am getting +20 static whenever I rig
>up the antenna.  I'm using speaker wire for the antenna and speaker
>wire for the ground.  Unhooking the ground seems to do nothing at all.
>Any antenna I rig up seems to just bring on the noise.  Unfortunately,
>I'm new at this so all serious suggestions wil be accepted. BTW, of
>course my apartment has a no antenna policy and I am on the first
floor.
>
>
>My new HTX 202 handie talkie seems to receive fine.  An old Zenith
shortwave
>radio picked up some stuff, real bad at times but I could usually find
>WWV.  I took the Icom over to a friend's house last night and on his
>antenna he got Mexico and Alabama just fine.
>
>[e-mail]


When you have 20 over 9 noise on an indoor antenna on the first floor,
there is good news and bad news.  The bad news is your antenna is really
close to the noise source (100 feet up would be far better), but the
good news is you won't have to go far to find it :->

Let's narrow it down.  Is the noise equally loud on all bands?  Your
antenna will have different responses on different bands of course, so
you need to allow for that.  One of the most common noise sources these
days is those touch-control lamps and their evil brothers, motion
detectors.  These have an oscillator which would normally be well
behaved, except that they feed it with raw, unfiltered pulsating DC.
This makes for harmonics which are frequency-swept back and forth at a
60 Hz rate.  The ones I have run across create a band of noise anywhere
from 30 to 250 kHz wide, with very sharp edges.  The sharp edge makes
them easy to identify.  For instance, the noise will cover 14.100 to
14.220 very loud, but at 14.095 or 14.225, it's completely gone.  The
band of noise tends to drift too, probably with temperature.  I have one
in my neighborhood that I could use as a thermometer if I wanted.  It's
not real loud, so I haven't gotten around to chasing it down.

If it's not that, then the times it's audible will help.  Flourescent
lights are a real noise generator.  Does the noise come and go like a
light being turned on and off?  If it's there 24 hours a day then it's
most likely a power line problem.  In a way, those are the easiest
because the power company will work with you, especially if you have
tracked it down some beforehand.

All this is leading up to what you really need to get serious tracking
it down.  A portable shortwave radio.  BTW, the HTX-202 is VHF and FM,
and therefore pretty much insensitive to this kind of QRN.  Use the
shortwave to walk around the neighborhood and get a fix on the noise.
If you find a suspected house, present yourself as a shortwave listener
(not a ham!) and inquire if they are having trouble, too.  They probably
are, especially if they use AM radios, so offer to check out the house
for them.  Most folks are quite receptive if you make it clear that
fixing the problem will help them, too.

And above all else, get the ARRL book on finding and fixing RFI.  It's a
gold mine of information.

One last suggestion:  horizontal loop antennas have a reputation for low
man-made noise pickup.  Just run it around the corner of your
wall/ceiling and make it as big as possible.  Feed it with a good
antenna tuner using open wire line and you'll be surprised how well you
get out!  I worked DXCC from an apartment here in Washington State
(where all the DX is a LONG ways away!) so it can be done.


73 es gl


Bill, W7LZP



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End of Ham-Ant Digest V94 #136
******************************