World of Ham Radio 1997/WOHR97_AmSoft_(1997-02-01).iso/antenna/ant_14/amsoft.iii

Text File | 1997-02-01 | 19KB | 431 lines

DIPOLE.DOC                       by:  Ira F. Kavaler - Aug, 1963
                     Major enhancements:  Sept, 1979 & Aug, 1990
Version 6.862 - 6/16/92


     This program will both design and analyze the performance of
dipole (single element) and doublet (multi-element) antennas.
Although these antennas are primarily used for both transmitting
and receiving, that property only makes their performance that
much better!


I.        Number of Elements.
          -------------------

     You will first be asked for the number of elements.  A one
element antenna of this design is a dipole, having a total
physical length of one half wavelength at the main resonant
frequency.  To be more accurate, an exact half wavelength antenna
at resonance (operating at the design frequency) would have an
input impedance of approximately 73 ohms.

     Since I use these antennas with 52 ohm coaxial cable (types
RG8/U and RG58/U), I have adjusted the design to provide antenna
lengths to match these types of transmission limes.  The errors
created for other common transmission line impedances, namely 75
and 300 ohms, are negligible.  A 300 ohm dipole would usually be
in the form of a "folded" dipole, having a one half wavelength
design formula, as would a straight 75 ohm half wavelength dipole.

     No effort has been made to revise or add formulas to take
into account the height of the antenna above ground, nor mutual
coupling amongst the elements.  In fact, the main antenna
radiation resistance formula has to be approximated by numerical
methods as it consists of a calculus formula that cannot be
integrated.  Further approximations are used to speed the massive
amounts of mathematics required for each element at each
evaluation frequency.  Some other electrical characteristics are
documented in graphical form rather than by formulas, and thus
formulas had to be derived from the graphs.

     A standard one element dipole will have one main resonant
frequency at which point the input impedance will be purely
resistive and match the transmission line impedance;  however, at
odd multiples of the resonant frequency the resistive portion of
the antenna input impedance will approach, but not reach, the
desired design level.  At a slightly different frequency, the
reactance portion of the impedance will pass through zero ohms.
Thus many dipoles are sometimes used at their third harmonic;
that is, three times the main resonant frequency.

     An antenna will be useable from a practical standpoint over a
frequency range of from approximately 2% below the main resonant
frequency to approximately 2% higher than this frequency.  This
characteristic is determined from the level of antenna impedance
to transmission line impedance mismatch, and is calculated from
the "standing wave ration" (SWR).

     A perfectly matched system (antenna and transmission line
operating at the main resonant frequency) will have an SWR of 1:1
(pronounced one-to-one).  As the operating frequency of the
transmitter is changed, the mismatch will increase to higher SWR
figures.  The higher the SWR, the higher the transmitter power
that will NOT be radiated by the antenna, but will be reflected
back down the transmission line to the transmitter output stage.

     At an SWR of 3:1, half the forward power will be reflected
back to the transmitter.  High levels of reflected power will
cause the following undesirable characteristics:

     1. the output stage of the transmitter will overheat and will
        eventually weaken the transmitting tubes or transistors,
        and could cause arcing across the plates of the
        transmitter tuning capacitors,

     2. the peak standing wave voltage level on the transmission
        line could exceed the maximum rating of the line, causing
        it to arc through the dielectric and be permanently
        damaged,

     3. the radio frequency (RF) fields cannot be contained within
        the transmission line, and will cause the line to radiate,
        becoming part of the antenna system, supporting
        significant radiation at the undesirable harmonic
        frequencies, which leads to RF interference, and

     4. the mismatch will reduce the efficiency of any in-line
        devices, such as filters, and increase the attenuation of
        the line beyond the characteristic loss figures published
        for that line.


     It is usually stated by manufacturers that the SWR should not
exceed 2:1 for most transmitters.

     If the operating frequency range (bandwidth) of a dipole is
insufficient then multiple elements can be requested, up to 5.  As
the resonant frequency difference amongst the elements is reduced,
the individual impedance of each element will "load" (detune) the
other element(s).


II.       The Automatic Design Mode and The Design Screen.
          ------------------------------------------------

     An Automatic Design Mode is now included which can be invoked
by entering the letter "a" instead of specifying the number of
elements.  Upon supplying the evaluation frequencies (see section
IV. below), the program will determine the antenna design that has
the minimum number of elements.  This design will completely cover
the desired frequency spread while maintaining an SWR under 2:1.

     Whenever the antenna design yields a wider frequency spread
than requested, the program will indicate the resultant minimum
and maximum frequencies for an SWR = 2:1.  You will also be given
the opportunity to align the antenna bandpass to the lowest or
highest evaluation frequency, or center the antenna bandpass over
the evaluated frequency spread.

     The design will proceed with the resonant frequency and
physical lengths of each element being computed and displayed.


III.      Element Resonant Frequency & part of The Design Screen.
          -------------------------------------------------------

     Next you will be asked for the resonant frequency of each
element of the antenna.  If more than one element was requested,
the resonant frequencies need not be entered in any special order,
and the physical length of that element will be displayed in feet
and inches.


IV.    Evaluation Frequency Range & the rest of The Design Screen.
       ----------------------------------------------------------

     Next you will be asked for the lowest frequency (starting
frequency) for the evaluation.  This need not be lower that the
lowest resonant frequency.

     Next you will be asked for the highest frequency (ending
frequency) for the evaluation.  This need not be higher that the
highest resonant frequency, and the evaluating frequencies will be
readjusted if entered in reverse order.

     As explained in section V. below, the program will select 41
discrete evaluation frequencies, equally spaced between the two
limiting frequencies you specify.  If any discrete evaluation
frequency happens to equal an even harmonic frequency of any one
of the elements of the antenna, the impedance of that element at
that frequency will be infinity.  This will cause a numeric
overflow in the computer, and usually result is the program
crashing (aborting).  Should this occur, simply re-enter the same
element resonant frequencies and either:


     1. lower the lowest evaluation frequency, or
     2. raise the highest evaluation frequency.


V.        The Table Screen.
          -----------------

     With all input data entered, the program will start the
evaluation.  The first screen will be a table containing a listing
of frequencies, SWR's and input impedances in polar notation
(magnitude of impedance in ohms at a phase angle in degrees).  The
listings will be displayed in red whenever the SWR exceeds 2:1, in
yellow over 1.5:1, in blue over 1.1:1, and in green below 1.1:1.

     The table will be in two sections to allow the evaluation at
41 discrete frequencies in the evaluation frequency range.  At the
top of the screen will be an indication of the number of elements,
a listing of the resonant frequencies of each element, the
physical length in feet and inches of the longest element, and the
geometric mean (average) resonant frequency of the antenna.

     In the full version of the program you can abort the
evaluation of the antenna during this phase by momentarily
pressing the [ESC] key.

     When the table is completed a flashing prompt will indicate
when to proceed to the next screen.  Pressing the key prior to
that point will not allow the table to be readable once completed.


VI.       The Graph Screen.
          -----------------

     In order to graphically see the performance of the antenna
system, the next screen will plot the SWR between 1:1 and 5:1 over
the evaluation frequency range.  If one or more of the element
resonant frequencies fall in this range, they will be displayed as
dashed vertical lines on the graph.  The critical SWR level of 2:1
will be displayed as a slightly heavier line horizontally across
the graph.

     When the graph is completed press any key to proceed to the
next screen.  Pressing a key prior to that point will not allow
the graph to be readable once completed.


VII.      The Chart Screen.
          -----------------

     The overall characteristic of the antenna system can next be
viewed from a Smith Chart which is based on a unit impedance of 52
ohms.  Only the most important lines of the chart will be
displayed along with a central circle indicating an SWR of 2:1.
The center of the chart is at a point where the SWR = 1:1, and the
outermost circle is where the SWR = infinity:1.
The starting (low) and ending (high) frequency points are denoted
on the plot.

     When the chart is completed press any key to proceed to with
the next antenna design, which will also permit termination of the
program if desired.  Pressing a key prior to that point will not
allow the chart to be readable once completed.


VIII.     Frequency List.
          ---------------

     The following list of frequencies is not meant to be
complete, nor has it been checked for accuracy with the latest FCC
issued frequency charts; its purpose is to supply information for
design purposes to users with limited technical knowledge.

Amateur Radio (Ham) Bands
-------------------------
Wavelength (name)        Low Freq.(MHz.)     High Freq.(MHz.)
160 Meters                   1.8                 2.0
80    "                      3.5                 4.0
30    "                     10.1                10.15   (WARC)
20    "                     14.0                14.35
17    "                     18.068              18.168  (WARC)
15    "                     21.0                21.45
12    "                     24.88               24.98   (WARC)
10    "                     28.0                29.7  (used to 29)
 6    "                     50                  54  (used to 51.5)
 2    "                    144                 148
1-1/4 "                    222 (as of 8/1/91)  225 (was from 220)
3/4   " (70 cm.)           420                 450 (used from 432)
                          1215                1300
                          2300                2350

     Amateur radio bands above 2350 MHz. have been omitted.  A
complete listing of authorized frequencies can be found in the
ARRL publication, "The Amateur Radio Handbook" as well as others.

Citizens Band (CB)
------------------
11 Meters                    26.96              27.45
Radio Controlled Models      72                 76
Cordless Telephones          46                 50
                       Note: Including short range walkie-talkies.

Commercial/Industrial/Governmental
----------------------------------
Low Band                     30                 50
High Band                   148                174
UHF (U-Band)                450                470
T-Band (old TV ch. 14-20)   470                512
800/900/Cellular Telephone  800                960 ? *
Aviation                    110 ?              136 ?
Marine Transatlantic          1.62 ?             1.8 ?


Broadcast Radio
---------------
AM (amplitude modulation)     0.535              1.605
FM (frequency modulation)    88                108

Broadcast Television
--------------------
Channel No.
2                            54                 60
3                            60                 66
4                            66                 72
5                            76                 82
6                            82                 88
7                           174                180
8                           180                186
Channels 9 through 13 follow logically every 6 MHz.
14                          470                476
Channels 15 through 83 follow logically every 6 MHz. although
channels 14 through 20 have been reassigned for commercial use and
are no longer available for TV service except under special
circumstances; for example, channel 20 in Connecticut.  Similarly,
channels 70 through 83 have been reassigned for commercial use and
are no longer available for TV service.

Note: The High Freq. is always 6 MHz. above the Low Freq.
      The picture or video carrier frequency is always 1.25 MHz.
          above the Low Freq.
      The color (chroma) subcarrier is always 3.58 MHz. above the
         picture carrier.
      The audio (sound) subcarrier is always 4.5 MHz. above the
         picture carrier.


IX.       Printing.
          ---------

     The design screen and the table screen can be printed by
using the computer's screen print function (pressing the keys
[SHIFT] and [PRT SC] simultaneously; however, since both the graph
screen and the chart screen require printer graphics you must
first execute under DOS your DOS utility GRAPHICS.COM before you
execute this program.  Each of the four screens can now be printed
using the screen print function described above, just wait until
the screen has been completed.


X.        Here's the small print.
          -----------------------

     This is a demonstration/trial version of the program.  It is
fully operational with all features;  however, when in the demo
mode, the data that you enter for the antenna parameters will be
used as design criteria but the performance evaluation will be
that of a two element doublet antenna designed to cover the entire
80 meter amateur radio band.

     All versions of this program including its related files are
being distributed on an "AS IS" basis.  There is absolutely no
stated or implied guarantee or warrantee of usability for any
purpose or correctness of the formulas and procedures contained in
any file.

     If you happen to discover an error in the program I will make
every attempt to correct the error as quickly as possible.  I am
under no obligation to replace nor make refunds for defective full
versions or demonstration/trial versions of the program.  I have
to take this posture as my cost to make even the simplest of
corrections far outweighs any monetary compensation received for
the full version of the program.

     If you require any special modifications to the program I
will be happy to discuss on an individual basis the cost of
supplying modified programs and documentation.

     The program was tested on a Tandy model 1000 using MS-DOS
3.2 and 3.3, a Tandy model 1000SX using MS-DOS 3.2 and 3.3, and an
IBM PS/2 model 50Z and 80, using PC-DOS 3.3.  All computers had
either CGA or VGA color graphics.  If your system has a Hercules
graphics adaptor, I suggest you obtain a color simulation program
such as SIMCGA.


XI.       And now a word from our sponsor.
          --------------------------------

     You can purchase the latest full unprotected version of this
program.  I will also include any other demonstration/trail
programs that I have available.  Please send $10.00 for one of the
following:

     1. IBM compatible 5-1/4 inch 360 kilobyte or 3-1/2 inch 720
        kilobyte disk, your choice,
     2. TRS-80 Model I or III 5-1/4 inch disk (only $5.00 as there
        is no Smith Chart nor Automatic Design Mode!)

to:
                          IRA F. KAVALER
                        671 East 78 Street
                     Brooklyn, New York 11236


     I reserve the right to discontinue support for, change the
terms, or withdraw any part or all of this offer including but not
limited to the programs and its associated files at any time
without giving prior notice.

     No form of this program may be used in commercial,
educational, nor governmental applications without written
authorization from the author;  such authorization may require
that a fee be paid to the author.


XII.      73's, de WA2ZIR.
          ----------------

     In 1963 while attending the RCA Institutes in New York City,
I was taught the most crucial equation to this program, the
radiation resistance calculus formula.  I was astonished at the
amount of time required to make even the simplest of calculations
with my K+E Log Log Duplex Decitrig slide rule, four man-hours.

     As an undergraduate at the Polytechnic Institute of Brooklyn
(E.E. class of '67), I became intrigued with digital computers.
My first computer program was written in machine language, along
with all required trigonometric subroutines, to solve this
formula.  The program was subsequently written in Fortran IV and
run on Polytech's IBM 7040 massive computer system.

     As soon as the first scientific calculator became available,
the Hewlett Packard HP-35, I was able to reduce the time to five
minutes, but there were a lot of keystrokes to enter.  Later I
purchased the programmable version using the famous chewing gum
magnetic cards, the Hewlett Packard HP-65 calculator.  The time
was now reduced to an amazing 45 seconds, and no more hundreds of
keystrokes.

     Through the years I have used this program, primarily written
in BASIC, to test the speed of various personal computers.
Believe it or not, for many years the Timex-Sinclair held the
speed record of 8 seconds.

     Recently I was amazed once more by a friend who allowed me to
use a Compaq 25 MHz./386 system in his office.  The table screen
was completed in a fraction of a second, and I gasped!

     I welcome your suggestions and comments about this product
and others.  I won't promise that good suggestions will be added
to the program, but they will be considered.


Thank you.


          Appendix.
          ---------

The operating systems, programs and companies mentioned in this
file:  MS-DOS, PC-DOS, LIST, BROWSE, SIMCGA, Hercules, Tandy and
IBM are all copyrights, trademarks, and/or service marks of other
individuals or other corporations.


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