Monster Media 1994 #1/monster.zip/monster/HAM/FMRNG304.ZIP/FMRANGE.DOC

Text File | 1994-01-09 | 14KB | 342 lines

FMRANGE.DOC                 by:  Ira F. Kavaler - April, 1982
Version 3.04 - 1/8/94


     A difficult answer.
     -------------------

     I have been an RF communications system design engineer for over a
quarter century now.  I am also an FCC licensed "Ham" (Advanced Class
Amateur Radio) Operation and "First Class" (General) Radiotelephone
Operator for over 30 years.  My Ham callsign is WA2ZIR.

     Whenever I lecture or teach on the subject of communications
system design or amateur radio, I am almost always asked the question:
"How far can you talk on it?"

     Most people, and at times I do to, answer this question with
examples on how far I have talked on my various systems;  for example,
it the discussion involves my conventional ham radio station, low band
frequency range, 1.8 to 30 MHz. single sideband station running 2,000
watt peak envelope power, my answer is all around the world!  I
describe my radio contacts (called QSO's, pronounced Q'sews) with
Russia, Japan, Hawaii, France, Germany, etc.

     If the discussion involves one of my 2 Meter FM "walkie-talkie"
(portable HT) in the VHF band at 146 MHz. running either 2 or 6 watts,
my answer is perhaps 10 to 20 miles, and I explain that I have made a
contact 100 miles away via a repeater station, which I go on to
describe.  My own 2M FM repeater station which I operated in the 1970's
was WR2ABX.


     What's the real answer?
     -----------------------

     There is no accurate answer, only results that are on the average
can be anticipated.  The range of an FM (frequency modulated) RF
communications system in the HF (3-30 MHz.), VHF (30-300 MHz.), or UHF
(300-3,000 MHz.) portions of the RF spectrum is evaluated from each of
the components in the system.

     There is a rule of thumb that I call "the 3 dB. rule", and that I
will refer to throughout this discussion, "You need a 3 dB. increase to
get more range."  This simply means that in order to get more range you
will have to increase a specific system parameter by 3 dB. before you
notice an effect.


     The communications system.
     --------------------------

     The system to a layman consists of two transmitters and two
receivers.  Although that is correct, it is far from complete.  The
complete system contains:  two antennas, two runs of cable connecting
the receivers and transmitters to their respective antennas, and lastly
the characteristics of the system and intervening terrain.


     Talk-out and talk-back.
     -----------------------

     Actually the system consists of possible two different ranges if
the transmitters and/or receivers are not the same electrically;  that
is, the transmitters have different power outputs, or the receivers
have different sensitivities.  Reciprocity is the term a communications
engineer used to describe the range of similarly equipped radio
stations when one wants to say that the range from one station to the
other will be the same as from the other station to the first.  When
the stations are significantly different;  such as, one is fixed (a
base station) and the other is portable or mobile, the terms "talk-out"
and "talk-back" are used;  "talk-out" is from the fixed station to the
other, and the reverse communications path, "talk-back" is from the
other to the fixed station.

     To determine the range of any system you must consider the weaker
of these two communications paths;  the weaker one will limit the
range.  As the old saying goes, "You can't work them if you can't hear
them."  This is an over simplification because it assumes that people
(and they usually do) devote far more effort in increasing their
transmitter power than improving their receiver sensitivity.

     If you cannot determine which path is the weaker this program,
FMRANGE, will do that for you once you try both paths and note the
respective system gains;  the weaker path will have the lower system
gain.


     System gain.
     ------------

     Each of the components in the system contributes to the overall
system gain;  it turn, the system gain is directly responsible for the
anticipated communications range of the system.


     Frequency.
     ----------

     The first and second most important characteristic in a
communications system is the operating frequency.  In general, as the
frequency goes higher the range goes lower.  Hurting that generality is
that:  as the frequency goes lower noise and interferences become more
of a problem.

     Although there is no restriction of entering a frequency in the
program, the data will be anticipated only between 3 and 3,000 MHz. (3
GHz.), the HF, VHF and UHF bands.  You do not have to enter an exact
frequency.


     Transmitter power output.
     -------------------------

     Starting with this characteristic the program will generate a
chart containing the following columns:

No.  System Parameter               Spec.         Gain/Loss (dB.)

No. is a number used to modify system parameters once a system has been
evaluated, and does not have a bearing on the system design.

System Parameter is the characteristic of the system being requested.
It will be followed by either a quantity in units (watts, microvolts,
feet, or decibels) or choices for other intangibles dealing with
terrain and surface conditions.

Spec. is the specified quantity or intangible choice you enter for the
particular system parameter.

Gain/Loss (dB.) is the contribution to system gain imparted by this
system parameter;  it may be helpful if it is a system gain having a
positive amount of decibels, or it may be a hindrance if it is a system
loss having a negative amount of decibels;  all must be considered.


     You will be asked for only one transmitter power as only one path,
talk-out or talk-back, is analyzed at a time.  The station site having
the transmitter is referred to as Sta. #1.  You enter the number of
watt of transmitter power output.  Any power greater than one watt will
add to the system gain.  The 3 dB. rule here means that you have to
double the transmitter power to see any practical increase in range.


     Receiver sensitivity.
     ---------------------

     As with the transmitting station, there will be only one receiving
station site in the system called Sta. #2.  The sensitivity of the
receiver is expressed in microvolts for either 20 dB.

     Sensitivities of less than 11.22 uV. will yield system gain;  the
usual specification for a RF receiver is these bands is 0.5 uV. for 20
dB. of quieting.  The 3 dB. rules here requires reducing the
sensitivity by approximately 30% before you see a practical increase in
range.


     Antenna Gain.
     -------------

     Every antenna system has an associated gain.  A simple dipole,
ground plane, or whip has a 0 dB. gain.  The longer or more elements an
antenna has for a given frequency band, the more gain the antenna has.


     Transmission line losses.
     -------------------------

     In FMRANGE this characteristic is termed Coax Loss although any
 type of transmission line may be used.  This loss is important to the
system design especially if either a small diameter cable (high loss),
high frequency, or towers are used.  Determine the length of cable
(transmission line) between the receiver/transmitter and the antenna
systems, multiply that figure by the loss of the cable in dB. per foot;
you may have to convert fro loss per 100 ft.  You cannot have system
gain from this characteristic.

     If your system has any in-line RF filters, cavities, duplexers,
isolators, circulators, amplifiers, etc. these should all be included
in this parameter.

     Keep track of Sta. #1 for the transmitting site and Sta. #2 for
the receiving site.


     Antenna height.
     ---------------

     This is the most important specification in any communications
system.  It is akin to a lighthouse.  As the high of a lighthouse is
increased (the lighthouse lamp is raised above sea level) the ships
further and further away can see it.  As EITHER the transmitting or
receiving antennas (or hopefully both) are raised above ground (sea)
level the long the communications range.  That's why you put broadcast
antennas on mountains, tall skyscrapers, or high antenna towers!  You
should do the same for receiving antennas.  Satellites circling 22,000
miles above the Earth are even better!

     This specification is expressed in feet above ground level, but if
you are on a mountain use sea level for both antennas.  Any height
above 6.25 feet will add to the system gain.  Keep in mind that
although height yield gain, if it is accompanied by excessively long
runs of transmission lines you are defeating the purpose;  that is,
mounting an antenna atop a skyscraper or mountain is better than a tall
antenna tower because in the former the transmitter can be located near
the antenna as opposed to ground level.


     Terrain and surface.
     --------------------

     The Earth is not flat!  I mean it has hills and valleys.  You
cannot see the lighthouse if there is a hill in the way.  The same
holds for radio waves.  Due to certain properties of electromagnetic
waves (radio signals), the signal is not totally lost, just degraded,
system gain is reduced.  Buildings, summer foliage and other obstacles
also reduce system gain.

     I have attempted to generalize these particulars in the last two
system parameters.  They will reduce the system gain to a maximum of 6
dB. each.  They are station independent, as they lie in the
communications path and are not part of any station site.


     The dessert.
     ------------

     Upon completing the above ten questions (entering the system
parameters) FMRANGE will calculate the system gain and range in miles.
If the system gain is not sufficient to yield a range of 0.2 miles,
that range will be indicated along with the additional amount of system
gain required to go above 0.2 miles.

     This latter figure is a guide to the minimum change required to
the system to yield minimum range;  if your desired range is not
achieved you will have to provide significantly more system gain.

     Increasing system gain.
     -----------------------

     System gain can be increased in a number of ways, some easy, some
hard.  The easiest way to increase system gain is to raise one or both
antennas.  Second, increase the gain of one or both antennas.  More
transmitter power is third and least desirable.  After that very little
can be done unless your receiver "is from hunger".


     Altering parameters.
     --------------------

     You can individually go back into the system and change one or
more system parameters and watch the effects on the system gain, range
and additional gain required.  The only parameter that will not allow
individual change is frequency, as most other parameters change when
the frequency changes significantly.  Different receivers and
transmitters must be used, different antennas are used, and the
transmission line losses change.


     Printing.
     ---------

     The design screen can be printed by using the computer's screen
print function (pressing the keys [SHIFT] and [PRT SC] simultaneously.


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

     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 Tandy models 1000 and 1000 SX using MS-
DOS 3.3;  IBM XT, AT, PS/2 models 50 and 80, using PC-DOS 3.3;  an
Arche Rival 286 using MS-DOS 5.0;  and a Compaq Desk-Pro 486/33 using
MS-DOS 6.0.


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

     You can get the latest version of this program by registering the
program.  When you register I will also include any other demonstration
/ trail programs that I have available.  Please send $20.00 for an IBM
compatible 5-1/4 or 3-1/2 inch 720 DS/DD or HD disk(s), your choice,
to:

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


     All inquiries that do not include the registration fee must be
accompanied by a stamped self addressed return envelope.

     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, registered or unregistered,  may be used
in commercial, educational, nor governmental applications without
written authorization or a site lease from the author;  such
authorization and/or site lease may require that a substantial fee be
paid to the author.


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

     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:
PKWARE, PKZIP, PKUNZIP, MS-DOS, PC-DOS, LIST, BROWSE, SIMCGA, Hercules,
Tandy Compaq, Arche, and IBM are all copyrights, trademarks, and/or
service marks of other individuals or other corporations.


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