SNAP501.TXT

          Signals, Noise and Propagation --- S N A P max v.501
          =====================================================

                  Crawford MacKeand  WA3ZKZ/VP8CMY
                  TYNDAR PRESS, Montchanin DE, USA.



                            CONTENTS
                            ========

             Subject                                 Page
             -------                                 ----

             Introduction                             2
             Shareware Version                        2
             Design Philosophy                        2
             Running SNAPmax                          3

             Typical SNAP Main Menu Appearance        3
             Main Menu Options                        4 - 6
             Presentation Menu Options                6
             Set-Up Menu Options                      7

             Noise Maps                               8
             Display Screens                          8
             Signal Level Calculations                10

             Path Gain Example                        11
             Ground Wave Signals                      11
             Descriptions of Aux. and Utility Files   12 - 13
             References                               14 - 15



                           N O T I C E
                          =============

       This program is available from freeware sources, and also from
       Tyndar Press, P.O. Box 236, Montchanin DE 19710  USA. Programs
       SNAP501.EXE, SNAP501.INI, and others listed in file README.501
       may be used, and may be copied and distributed freely, if they
       are completely unmodified, for personal non-commercial amateur
       use only. No warranty of any sort is expressed or implied; the
       user is presumed to understand the  limitations & inaccuracies
       inherent in such programs. These programs are Copyright (c) by
       Crawford MacKeand 1992,1994,1995,1996,1997,1999 & 2001 and may
       not be sold or rented or otherwise disposed of by way of trade.
          For all other uses please contact the author directly.


       References in the following text to SNAPxxx.EXE etc. should be
       read as referring to the version number actually provided. You
       would read SNAPxxx.INI as SNAP501.INI if you had that version.



                                         1


       FREEWARE VERSION
       ----------------

       You are encouraged to distribute this program to your friends as
       freeware. To do so, delete file SNAPxxx.INI and give them everything
       else. SNAPmax will generate a new .INI file on user request.


       INTRODUCTION
       ------------

       "SNAPmax" is designed to be flexible and yet easy to use, presenting
       the probable workability of an ionospheric radio path between any two
       sites, and ground wave to local sites, using algorithms from many
       sources. The MUF code is by R. Fricker of BBC Overseas Services, and
       SNAPmax itself builds on the basis of my earlier program, SNAP which
       was inspired by KD6SC's program DX-DOS.BAS. His ideas for screen
       layout are used and are gratefully acknowledged. SNAPmax was coded and
       compiled in Microsoft QuickBASIC (TM).

       The analysis uses the angle of ray elevation, to obtain realistic gain
       values for some typical antennas at those ray angles, and path
       attenuation values based on the NBS Monograph 80 (Ionospheric Radio
       Propagation, Kenneth Davies, Dover), K. Rawer's classic analysis, and
       a number of other sources. For farther Northern (and Southern) users,
       I also include a unique determination of probable auroral losses. To
       this mixture, I have added my algorithms for the CCIR noise maps,  so
       that a signal to noise ratio can be presented for each time and
       frequency, taking into account atmospheric, man-made and galactic
       components of statistically expected noise levels for season and time
       of day. Both F layer and E layer paths are calculated, and this latest
       version also includes some ground wave calculations from CCIR 386-2.


       DESIGN PHILOSOPHY
       -----------------

       SNAPmax uses a design concept more familiar in cost estimating for
       engineering projects than elsewhere. It holds that any known trend
       should be included, with the basis that, while some inputs will be
       underestimated in their contribution to the final answer, others will
       similarly be overestimated. Thus the sum of the estimates will be
       better than the individual parts.

       The use of SNAPmax will be, I believe, mainly in "nowcasting". This
       is the prediction of the goodness of any given circuit today, based
       on today's best data. Broadcasters and commercial users are often
       more interested in forecasting what will happen next month or even
       next year, so that they can best plan frequency and equipment
       utilization. (And ionospheric physicists are often interested in
       "hindcasting", where the question might be "I wonder why that route
       didn't work out the way we thought it would!"). I don't think that
       long term forecasting is too useful to most amateurs (although major
       contest stations certainly can and do work this way.)  Rather, when
       we go into the shack we want to know what is open (and maybe why!)




                                         2


       The 'analysis' presentation is, I think, unique to SNAPmax in telling
       you quickly why a given route will or will not give good signals, as
       it will show the contributors to path loss, path probability where you
       are well over the maximum usable frequency, and relative importance of
       noise sources.  I hope that, where a path appears to be closed, this
       may help you select another time or a more appropriate frequency.


       RUNNING SNAPmax
       ---------------

       SNAP is DOS based, and although Windows (TM) is not needed, it will of
       course run under Win95 or Win98 very satisfactorily. For preference,
       use a Pentium or 486. A 386 will work, but XTs are much too slow. SNAP
       can run monochrome, but it is not recommended, as too much information
       is lost to the viewer. To run SNAPmax, load a disk or directory with
       SNAPxxx.EXE SNAP.QTH & SNAPxxx.INI which MUST be filed in the same
       disk or directory. The ONLY renameable file is SNAPxxx.EXE (which may
       be called SNAP500.EXE, SNAP501.EXE  etc. to distinguish the release
       versions.) If you name it SNAP.EXE then enter SNAP<CR>, and after a
       personalized introductory screen the display will resemble that shown
       below. To run SNAP for an initial demonstration, just press <SPACE>.

       ----------------------------------------------------------------------
       |                                                                    |
       |               S N A P m a x   from   W A 3 Z K Z                   |
       |  SIGNALS, NOISE and PROPAGATION  - by -  Crawford MacKeand (V.xx)  |
       |                                                                    |
       |  D T    Date   Time GMT                15 Feb  1999    01:39       |
       |  S (N)  Solar Flux & A Index           188             15          |
       |  P      Power & Required Bandwidth     120    Watts    500  Hz     |
       |         Receive Noise Level            Suburban        R           |
       |         Antenna Types, Local & Remote  3 El Beam       Dipole      |
       |                                                                    |
       |  L      Local (Receiver) Name        Your Call                     |
       |         Local Site Location          40  North   100  West         |
       |  R (C)  Remote (Transmitter) #1      London (G)                    |
       |         Remote Site Location         51.5  North   .1    West      |
       |                                                                    |
       |  Mode   Signal-noise ratio (S-Units) shown vs frequency and time.  |
       |  B      Bandwidth & signal/noise for modulation type vs freq/time  |
       |  H      Hard copy is OFF             W Write to Memory is OFF      |
       |  E      Enter set-up, default and information menu                 |
       |                                                                    |
       |      Press option letter, or <SPACE> to compute, X to exit.        |
       |                                                                    |
       ----------------------------------------------------------------------

          ***************************************************************
          *                                                             *
          *  At first start-up enter 'E' to go to the set-up menu, and  *
          *  then an 'O' to enter your call and location, and for your  *
          *  local noise map values.  Finally an 'S' will save to disk. *
          *  A more comprehensive set-up is accessed with keys E and O. *
          *  You may also set the computer time offset from  GMT (UTC). *
          *                                                             *
          ***************************************************************


                                         3


       Site selection is normally by call sign prefix, but US states are
       also included in the form 'STDE' for Delaware, 'STOH' for Ohio etc.
       [Keyboard entries may be either upper or lower case.]  Latitude and
       longitude can also be used.  To exit from SNAPmax enter X (twice).

       The following notes describe how all other possible options can be
       used from this screen.  But use 'E' menu options as noted in the
       previous paragraph to insert your call and location before making
       real use of the program.  SNAPmax can thereafter use your own local
       noise figures instead of an approximation.

       [Noise data for the ten call districts of the continental  U.S.A.,
       for Alaska and Hawaii, for the eight Canadian areas, and for some
       other countries listed below is imbedded in SNAPmax].


       MAIN MENU OPTIONS
       -----------------

       F   Frequency.
       This is only required for the Band Opening and Analysis screens, and
       is only shown when required, but a new value can be entered and shown
       at any time using the F key.

       D   Date & Time GMT.
       This screen will initially ask if you want to make a change (enter
       SPACE), or retain present time [computer clock based] by pressing
       ENTER <CR>. If you want to change, you can enter Year, Month, Date,
       Hour and Minute in turn. For each one, you are told the present value
       in memory, and offered the opportunity of retaining it by pressing
       ENTER. [Many users do not set their computer clocks to GMT (UTC),
       and a time zone adjustment option is stored in file SNAPxxx.INI,
       modifiable from the Set-Up screens.]

       T  Time.
       This short cut entry allows you to change time only. It also allows
       you to retain the computer time used for previous computations, so
       that continual resetting is not necessary if you have a series of
       calculations to make.

       S  Solar Flux.
       On entering S, you can select a new value for the 10.7 cm Solar Flux
       and also for the A Index or the K Index, all of which are available
       from WWV at 18 minutes past each hour and from a number of sites on
       the Internet. SNAPmax uses the A (or K) index to make an appropriate
       correction to Maximum Usable Frequency (MUF) for ionospheric storm
       conditions. (If you don't know the A Index leave it as 12. Or if
       conditions seem better, you might set  A = 2; if bad, say A = 25).
       For reliability, use recent K values.
       [Sunspot Number can be used instead of flux. See the next entry.]

       N  Sunspots.
       If you prefer to enter Sunspot Number, then enter N instead of S. You
       will be asked for Sunspot Number, and this will be converted to Flux.
       The Sunspot Number is presented for verification on returning to the
       Main Menu, but only on first returning. The A or K index can also be
       entered for the storm level.


                                         4


       P  Power.  (Required Bandwidth).  Receive Noise Level
          Antenna Types and Heights, Local and Remote.
       You can enter a transmitter power from 1 to 500,000 Watts. [This large
       value is allowed for the benefit of broadcast SWL users.] The required
       bandwidth is set automatically when the modulation is selected. [See
       entry B below]. Your local noise situation can be selected here. It is
       displayed as Urban, Suburban, Quiet, etc., as also is a label for the
       atmospheric noise table in present use.

       The antenna types precalculated are the three most popular ones,
       3 Element Beam, Dipole & Vertical. (Other options such as isotropic
       antennas may also be selected from the Set-Up (EO) screens, where
       you can also enter your own antenna gain values and display the dB
       gain values for your entries and for internally calculated antennas.
       The vertical is presumed to be ground mounted; for the others any
       height from 10 to 300 ft. may be selected. Internal calculations
       also allow for feeder loss, assuming use of RG-8 coaxial cable.


       L  Local Site Name.      Typically, your call sign.
          Local Site Location.  Geographic co-ordinates.
       If you enter L, you are asked to enter a call prefix. Enter your
       choice and it will be shown, with its name, prefix and location. You
       can enter "Q" instead of a prefix; you will then be asked to enter
       Latitude and Longitude (degrees). If you enter an incorrect prefix,
       you are shown the available list with the same initial character. You
       can also ask for this list to be displayed from the "E" entry below.

       Using the "L" option, the local atmospheric noise calculation is very
       approximate. (More detail below. This condition is flagged by a red
       color for the indicator.) For the default local site, I don't display
       your prefix as I assume you know it very well! But it reminds you that
       you are in normal mode with full noise data.


       R   Remote Site Name.
       (C) Remote Site Location.
       These are similar to the local entry. The remote prefix is always
       shown. If you enter "Q" for the prefix, you'll be asked to provide
       Latitude and Longitude in degrees.  If both sites are selected to be
       the same, inadvertently or for NVIS (Near Vertical Incidence)
       propagation, remote latitude and/or longitude will be increased by
       0.1 deg to give a calculable minimum path for a zero length entry.

       You can save details of up to three remote sites, and these can be
       selected by pressing C to select any of them in turn. Only the active
       site is saved at any one time, the others are protected in SNAPxxx.INI
       A fourth "site" provides a ground wave calculation for local contacts.


       M  Mode of Presentation.
       Entering M will take you to a new menu, where you can select from a
       number of choices for the presentation, either with a pointer or by
       entering a keyboard code.
       [A description of the mode entry menu will be found on page 6.]




                                         5


       H  Hard copy.
       This is a toggle and will give hard copy on any standard printer from
       the main sky-wave propagation screens.


       B  Bandwidth and Modulation.
       Entry from this screen allows you to select your operating mode, those
       available being PSK, CW, RTTY, TOR, SSB, AM, FM, and BCAM. The required
       band width is automatically entered, as also are the signal-noise
       requirements for Good, Median and Fair signals. As in the main scan
       modes, probable multi-path conditions are flagged for digital work.
       The set-up data for this mode is also saved separately.


       E  Set-up, default and information.
       The set-up screen provides a variety of options which are fully
       described below on page 7.


       X  Exit to SYSTEM.
       You get a second chance if you hit X by accident as in order to exit
       from the program two consecutive X's must be entered!


       <SPACE>  Compute.
       Press the SPACE bar to start any calculation.

       [This completes the option list for the Main Menu itself.]


       PRESENTATION MODE OPTIONS
       -------------------------

       The following choices can be selected with the pointer or by entering
       the code letters shown. To use the pointer, step through the menu
       by pressing either the <SPACE> bar or the up/down arrow keys, and
       then select the entry by pressing the ENTER key. Or you can just
       enter the two letter code shown. The main screens are in two parts
       to handle all 24 hours of the day, although hard copy is not so
       divided. (To escape between parts, press ENTER instead of SPACE.)

       QC  The goodness of the circuit for the selected modulation scheme
       (RTTY, SSB, CW etc.) is displayed as "G" (Good) "M" (Median) or "P"
       (poor) against time and frequency.

       SN  A signal-noise 'map' against time and frequency is plotted.
       Signal-to-Noise ratio is in S-Units (6dB).

       DN  The same as SN, but with Signal-to-Noise ratio in units of 10 dB.

       SS  A similar 'map' is plotted, but for signal-strength against time
       and frequency.  Signal is in S-Units of 6 dB with S9 defined as a
       level of -73 dBm in the receiver. [S0 is therefore -127 dBm.]

       DS  The same as SS, but with signals in units of 10 dB.

       BO  The Band Opening screen, providing Good, Median, Poor and Closed
       status for 15 sites preselected from the ER set-up menu.

                                         6


       CC  The 'analysis' mode gives many calculated values for noise, signal
       strength etc., both graphically and in tables, so you can see for
       yourself that the results make sense. It examines the two most likely
       paths for MUF, attenuation etc.

       NF  Presents noise levels vs. freq. for your time and location.

       LF  Switches the frequency basis for the scans from  2 - 50 MHz (the
       default range) to 2 - 12 MHz, for low band use, such as NVIS etc.

       CH  Toggles "chordal hop" mode. Transequatorial paths are typical,
       usually transiting the dark side of the earth. SNAPmax emulates a low
       attenuation "whispering gallery" path in which repeated reflection
       from a non-spherical ionosphere replaces many lossy earth reflections.

       LP  A toggle that selects the "long path" round the world.

       (This completes the option list from 'M' entry in the Main Menu).


       SET-UP MENU OPTIONS
       -------------------

       The following options are offered.

       D  Return to the default values in SNAPxxx.INI. This is the best way
       to restore full use of noise map data after using the main menu 'L'
       option. (Though you could more laboriously use 'O'!)

       P  Select the presentation mode you want to use for start-up default.

       C  Update the default file. This option, taking the present screen
       data, saves it as a new default set in SNAPxxx.INI; especially useful
       to update one of the three saved remote sites. [Remember that only the
       active site can be saved .... the others are protected.]

       F  Read a file of background information, including reference list.

       O  Set up the default options. You need your callsign, geographical
       latitude and longitude, a noise map code, [see "Noise Maps" below],
       time zone adjustment to GMT [or UTC if you prefer!], and some other
       data, for which you'll normally accept default values provided.
       [A 'basic' option provides a simple set-up to get started.]

                 ----- Some tips for the set-up procedure. ----

             Normally you will likely use internal antenna gain values. Press
             ENTER (or key in INT) to select internal values. However you can
             enter your own antenna gain data. Key in NEW to access an entry
             screen, which accepts your dB gain data at 24 elevation angles
             from 1 to 90 deg, for remote and/or local antennas. Internal and
             external values can be used in any combination. Press REM to use
             external remote values, LOC for local values or EXT for both.
             Enter ISO for isotropic antennas in both locations. An entry
             PRN will display all values, your own or internally calculated.
             Minimum elevation angle is something you must decide on. In a
             small backyard, 7 - 10 degrees may be appropriate. From a
             headland overlooking the ocean, 1 degree maybe!

                                         7


             Next select whether your printer requires a form feed, and what
             character you want to use for FOT print-over.

             And finally the clock adjustment for GMT as already mentioned.

             To complete the set-up you have the opportunity to save to
             SNAPxxx.INI or make your escape to try again if necessary.


       N  If you are located outside the USA or the other most populous
       countries provided internally, then you will want to enter your
       atmospheric noise values from the CCIR maps as published in CCIR
       Report 322, also in the book by Saveskie. [See the references below.]
       A total of 24 values is required, normally between 20 and 100 dB, one
       from each map. These are noise values for your location at 1 MHz, and
       should be entered in the order in which the maps are printed.  It
       helps to have made a list on paper before entering this option! Values
       are saved in SNAPxxx.INI with the usual escape option.

       L  Obtain a list of countries. You will be asked to input the first
       character of the prefix.

       R  Remote countries list for band-openings accepts 15 prefixes for
       saving to SNAPxxx.INI.  You do have to ensure that the prefixes you
       enter already exist in SNAP.QTH, and this can be checked out first
       with the 'L' facility.

       X  Exit. Returns to the main menu without action.

       (This completes the option list from 'E' entry in the Main Menu).


       NOISE MAPS
       ----------
       Noise data for many sites has been extracted from the CCIR maps and
       tabulated in the data files used by the 'noise' sub-routine. These
       sites in the United States are the FCC call areas, 1 through 0, Alaska
       & Hawaii, and for Australia and Canada they are your prefix areas.

       The Set-Up option change entry requests simple codes which are noted
       on the set-up page. The countries available are, as well as the above
       CE, CX, DL, EA, F, G, GM, GW, HB, I, JA, KP4, OH, ON, PY, TI, UA, VP8,
       ZL and ZS. You can also enter the code letter "R" which will give an
       approximate noise map for the Rest of the world. [It uses one basic
       set of data (for US call area W1) and modifies it for latitude].  Code
       L selects a table which you have entered as a default selection, as
       described above. Until you have saved your own data in SNAPxxx.INI,
       this option remains closed.

       The R code is principally used if you select a new local site from
       the Main Menu, usually for some temporary interest. Your own more
       accurate noise conditions will be re-instated if you use option D
       in the set-up menu [or work your way through options O or B or just
       exit and start over.





                                         8


       DISPLAY SCREENS
       ---------------
       The simplest screen "QC", shows circuit quality "Good, Median, Poor"
       for the selected signal mode, based on signal-to-noise ratios needed
       by the different modulation schemes. However, to see the fundamental
       features of 'SNAPmax'  use "SN", for signal to noise ratio, and that
       using S-unit values is the distributed default. All you need to do to
       see a sample screen on startup, is to press <SPACE>. The screen
       display is very simple although it does contain a lot of data.

       This description refers to the signal-noise screens, but the signal
       screens are very similar. [But note that the Lowest Usable Frequency
       or LUF is not going to be the same in both. In SNR screens, it means
       that the SN ratio is better than -6 or -10 dB. In signal screens, it
       means the predicted level is above -6 or -10 dB ref. S0, where S0 is
       -127 dBm at the receiver input.)

       A blank space says that there is not likely to be enough signal for a
       useful QSO. A dot (.) says that signal/noise ratio is up to 1 S-Unit
       below noise. A number in any space, and its associated display color
       in that space will show by how many S-Units, (which are arbitarily set
       at 6 dB each), your desired received signal will exceed your local
       noise level. A plus sign (+) indicates that predicted signal level is
       more than 9 S-Units over noise.

       A star (*) shows that this signal [the level being indicated only by
       the color] is above the Maximum Usable Frequency or MUF and is
       probably present only 10 days in the month. A dash (-) shows signals
       probable on 5 days of the month. MUF is, as usual, defined as the
       maximum operable frequency on 15 days of the month, while the FOT
       (abbreviated from the French term 'Frequence optime du travail'),
       which is about 0.8 x MUF is defined as likely to be operable on 27
       days of the month. (90%)  FOT is shown by a magenta background if a
       signal is likely to be present, or a narrow magenta stripe if no
       signal is predicted.

       Colors are white S7-9+, light cyan S4-6, blue S2-3 and black S0-1.
       In the QC screen, signals above the MUF are shown in red/brown.

       If signals are as strong as they may be if you are using the program
       for BC SWLing, you can select main menu option M and then option DN
       (or DS) in the presentation menu for 10 dB steps above a 0 dB base,
       instead of 6 dB S-Units.

       The screens give circuit performance for each hour of a 24 hr. day, at
       frequencies from 2 to 50 MHz, or optionally (LF) from 2 - 12 MHz.  The
       S/N ratio or signal displayed is the better of the two most probable
       paths. [For digital signals, if the two paths give signals within 10
       dB of each other and the probable delay is large enough to cause
       decoding problems, then a green background shows this as a possible
       multipath condition.]

       The program takes into account changing MUF and antenna gains etc. as
       the number of hops changes, & likewise the elevation angles. As well
       as showing LUF and MUF, these screens will flag whether any paths or a
       majority of paths at the given GMT hour are propagated via the E layer
       by displaying 'e' or 'E' respectively at the end of the line.


                                         9


       The 'analysis' screen provides more data on both paths, with MUF, foE,
       foF2, the number of hops, skip distance, probable circuit availability
       in terms of MUF, and a breakdown of noise sources and path attenuation
       factors.  To avoid confusion, although all calculations appear for
       zero probability paths, the symbols for signal-to-noise and s-n ratio
       (dB), are shown in a distinctive red-brown color, and over-MUF loss is
       displayed. The E layer cut-off for F layer paths will likewise show
       up with a similar color change. Two color strip pages depict signal-
       noise, noise make-up and signal loss, including the Good, Median and
       Poor SN ratios for the selected modulation scheme.

       The Band Opening screen also inserts target values for signal-noise
       ratio against which the Good, Med. etc. decision is made. Potential
       multipath problems are flagged with a green background. If a path
       may be Open at frequencies above MUF, instead of Good, Med., Poor
       flags it shows a small magenta field with % chance of a signal.
       [The data line color will still give a clue on the possible SNR!]

       The signal-to-noise levels chosen for Good, Median & Poor are given in
       the table below. Most data is from CCIR. [G3PLX states that Good PSK31
       needs 14 dB SNR in a 31 Hz bandwidth.] SNAPmax interprets 'Closed' as
       no copy and 'Poor' in digital modes as 5% Character Error Rate (CER).

                     MODE        Good   Median  Poor   Closed   Bandwidth

                      FM          40 dB   35     30      25      15000 Hz
                      BC AM       45      35     25      15       9000
                      AM          34      24     14       4       6000
                      SSB         32      22     12       2       2600
                      RTTY        26      18     10       2        500
                      TOR         23      13      3      -7        500
                      CW          17       7     -3     -13        250
                      PSK31       14      11      8      -2         31

       The RTTY signal is 45 Baud narrow shift [170 Hz], TOR assumes a link
       at 100 Baud, and CW is 8 Baud (20 wpm)


       SIGNAL LEVEL CALCULATIONS
       -------------------------

       Received signal levels are detailed in the 'analysis' screens, and
       depend on the transmitted power, distance loss, absorption losses,
       reflection losses mainly at intermediate earth points, and over-MUF
       loss for signals above the calculated maximum usable frequency.
       [If you try to check the calculations against the NBS method, you will
       find that the distance loss calculation is not exactly the same, being
       based on the slant range calculations of K. Rawer.]

       There are also losses in the auroral zone, depending on ionospheric
       disturbances, and antipodal focusing gains, which depend conversely on
       a smooth undisturbed F layer.  Antenna gains are also included. It may
       be surprising to see the real antenna gains. Forward gain is often
       quoted as the maximum of the best lobe, and in practice the ray angle
       required may be something else entirely. Calculations are based on a
       summation of several ELNEC models to allow for gain changes due to the
       antenna height above earth, assumed to be of medium conductivity and
       flat. The vertical antenna is assumed to be at ground level.

                                         10


       You cannot just add up all these losses and gains to get from the
       transmit level to the receive level in dBm, but must apply the proper
       constants to go from antenna input to free-space signal in dB with
       reference to 1 microvolt / meter, then the sum of the losses and
       gains, and finally another conversion from space-signal to the induced
       level in an isotropic receiving antenna, which is also frequency
       dependent. The references by Rawer and David & Voge give much more
       detailed explanations. Here's an example at default conditions as
       distributed, 14.2 MHz, 21 July 1993, 0030 GMT, so you can see how it
       works. (Accuracy to 3 decimal places is NOT implied!!)

       PATH GAIN EXAMPLE
       -----------------

           Transmit power                50.791  dBm
           (Signal at 1 km. = transmit power + transmit antenna gain + 74.8)
           Signal at 1 km from xmtr.    126.310  db ref 1uV/m

           Distance loss                 95.221  dB
           Absorption loss                8.247  dB
           Auroral zone loss              3.416  dB
           Over-MUF loss                  0      dB
           Reflection loss               11.816  dB

           (Recv location sig = sig at 1 km. - total losses)
           Recv. location signal          7.608  dB ref 1 uV/m
           (Recv sig = recv loc sig + recv ant gain - 20 log F MHz - 77.2)
           Received signal              -83.489  dBm


       GROUND WAVE SIGNALS
       -------------------

       Beyond the skip zone, signals are returned from the ionosphere, but
       between your station and the near edge of the skip zone [if indeed it
       there is one in a given situation], ground-wave propagation holds, and
       this obeys quite different rules. It depends very much for instance on
       the earth conductivity between transmitter and receiver. Propagation
       data for ground wave signals is from CCIR 368 which assumes short
       [less than 0.1 wavelength] vertical antennas and 1 kW power.

       The CCIR curves for medium conductivity ground have been converted to
       algorithmic form and included in SNAPmax. [Results would be much
       enhanced over sea water and much poorer over a desert.] A screen can
       be accessed by calling up remote site #4 from the main menu with 'C',
       and displays the signal-to-noise ratio from 2 to 28 MHz, for distances
       in km. depending on the power and antenna selection.

       Antenna gain is not the same as for sky wave operation. SNAPmax uses a
       quarter-wave vertical antenna [quite an antenna on 80 meters!] as the
       default case. If you select a dipole or 3 element beam instead, you
       will see why verticals are used for ground-wave work. If you check out
       the effect of cross-polarizing the antennas, you find an intermediate
       result. The propagation loss with the use of horizontally polarized
       antennas is approximately 50 dB, compared with vertical polarization.
       In the mixed case, we are dependent on both the propagation losses and
       on cross-polarization losses at the antenna. Even a dipole in the real
       world has some vertical component, and a study with ELNEC showed that

                                         11


       with a reasonably imperfect location with guy wires, masts etc., 25 dB
       cross-polarization loss would be a fair estimate.

       Note that the frequencies above 12 MHz are derived from a different
       set of CCIR curves, and may not be as reliable as lower frequency
       data. This is indicated by the color change on the frequency scale.
       The Site #4 selection will only access the ground wave calculation and
       cannot be used for any other purposes.


       DESCRIPTIONS OF THE AUXILIARY AND UTILITY FILES
       -----------------------------------------------

       SNAP.QTH
       --------
       A random access file of prefixes, latitudes, longitudes and country
       names. The prefix contains up to four alphanumeric characters, and
       the country name may have up to 24 ASCII characters. (But note that
       any entry with more than two adjacent spaces, i.e. Spratly   Island
       will have the extra spaces removed automatically after entry. Which
       minor quirk eased my life in writing the program!) To update, use
       the special editor SNAPQTH.EXE.


       SNAPQTH.EXE
       -----------
       SNAPQTH.EXE is a purpose-built editor making it easy to add, modify
       or delete entries. It must be in the same directory and on the same
       disk [in the same folder if you speak Windows!] as SNAP.QTH, and
       operation is very straightforward and menu driven. It will not allow
       any entries not meeting the limitations required by SNAPmax, and flags
       out-of-limits entries. It also lets you try again if you blew it with
       any entry. New entries are placed first in empty (deleted) slots and
       secondly at the end of the file.

       [If you ever conclude that your SNAP.QTH needs complete rework, you
       can start over with the two files described below, though they are
       mainly included for compatibility with SNAP27 & earlier versions.]


       SNAP.DAT
       --------
       A sequential file of prefixes followed by latitude, longitude and
       name. A typical series of entries will appear as shown.

              "G",51.5,.1,"England"
              "YV",10.5,67.5,"Venezuela"
              "ZD8",-8,14.3,"Ascension Is."
              "STOH",40,83,"Ohio"
              "WASH",38.9,77,"Washington DC"

       It can be inspected, modified or added to, with an editor such as
       E88.EXE or the Norton Editor. A word processor would have to produce
       an ASCII file with no format characters. Only disk space limits
       countries you can add to this file. The maximum space for a country
       name etc. is 24 chars. Any more are truncated and will be lost.



                                         12


       Where they don't clash, old and new prefixes are both there. A few
       major cities, e.g. "NYNY" and "LOND" are there, and all US states are
       included in the format "STDE" for Delaware, 'STOH' for Ohio, [ST + US
       Post Office Dept. standard State abbreviations.]

       [SNAP.DAT file is for reference only, and is NOT used by SNAPmax. It
       was however up-dated in May 1999.]


       REFILE.EXE
       ---------
       If you inadvertently delete SNAP.QTH, or would like to build your own
       for some reason, use the information in the previous paragraph. Or
       starting with SNAP.DAT included, run REFILE in the same disk and
       directory. It converts SNAP.DAT to SNAP.QTH and allows you to read the
       new file. It will also read SNAP.QTH at any time. You may never use
       REFILE, but as I wrote it to help in the sequential to random data
       file conversion, here it is.


       SNAPxxx.INI
       ----------
       This little file will contain your preferences for starting up SNAP.
       These include [not necessarily in order]:-:

            o the minimum ray elevation angle
            o the selection of Form Feed or not for your printer
            o time adjustment from your computer time to GMT
            o the default frequency (used in the 'analysis' and
                'band opening' screens)
            o the antenna description for your own station
            o selector for internal, external, isotropic antennas
            o the height of your antenna, and a descriptor code.
            o the antenna descriptions for the remote stations, and
                the heights of their antennas.
            o the assumed power of the remote stations

            o the local station description (usually your call sign)
            o the noise area code, described above under 'Noise Maps'
            o latitude and longitude for your site
            o prefixes for the remote sites (don't change them here!)
            o the names for the default remote sites
            o latitudes and longitudes for the default remote sites

            o the default 10.7 cm solar flux (100 as distributed)
            o the default A index (12 is the historical average)
            o default modulation systems, SSB, CW, RTTY etc.

            o display name for man-made-noise level
            o basis level for selected man-made-noise level

            o the 15 prefixes selected for the band opening screen.
                They can be changed from SNAP.
            o 24 entries for your local atmospheric noise base. [The
                negative values in distribution and default files tell
                SNAPxxx.EXE that no data has yet been entered.]
            o 48 entries for your own antenna dB gains vs. elevation.


                                         13


            o antipodal focusing % [set at 25 initially].
            o default start-up mode entries.
            o a series of numbers used internally by SNAPmax.

       If the file is damaged, it will normally tell you quite clearly!
       You should delete it and replace it with the distribution copy.



       The book "The FRIENDLY IONOSPHERE" by Crawford MacKeand describes
         many basic mechanisms of SNAPmax. It is readily available from
             Tyndar Press, P.O. Box 236, Montchanin, DE 19710 USA


       REFERENCES
       ----------
       Electromagnetic Waves and Radiating Systems, Edward C. Jordan
          Prentice-Hall, NY, 1950
       Short-Wave Radio and the Ionosphere, T.W. Bennington, Iliffe,
          London 1950
       Calculation of Sky-Wave Field Strength, K. Rawer, Wireless Engineer
          London,  Nov. 1952  p287-300
       Compendium of Technical Regulations, CCIF, CCIT, CCIR of the
          International Telecommunications Union, "The Red Book",
          Automatic Telephone & Electric Ltd., Liverpool, 1956
       The F-Region during Magnetic Storms, Maeda K.I. &  Sato T.
          Proc. I.R.E.   Feb. 1959  p232-239
       Handbook for CRPL Ionospheric Predictions based on Numerical
          Methods of Mapping (Handbook 90),  U.S. Dept. of Commerce,
          National Bureau of Standards, Washington DC 1962
       Radio Wave Propagation and the Ionosphere, Al'pert, Y.L,.
          Consultants Bureau NY 1963 (trans from Russian)
       A New Ionospheric Reduction Factor [Multipath], Salaman R.K.,
          I.R.E. Trans. Commun. Syst. CS-10, 1962
       International Radio Consultative Committee, International
          Telecommunications Union, Geneva, Report #322 1964 (NTIS
          Document PB 255 060, US Dept. of Commerce, Springfield VA)
       Ionospheric Radio Propagation, Kenneth Davies, Dover, NY 1966
          (National Bureau of Standards, Monograph 80, 1965)
       Propagation des Ondes, David P. & Voge J., Eyrolles Editeur,
          Paris, France 1966. (in French, see 1969 trans.)
       Predicting Long-Term Operational Parameters of High-Frequency
          Sky-Wave Telecommunication Systems,  Barghausen A.F.,
          Finney J.W., Proctor L.L. & Schultz L.D.  ESSA Tech. Report
          ERL 110-ITS 78   NTIS N70-24144 Springfield Va., 1969
       The Radio Communication Handbook, Radio Society of Great Britain,
          (RSGB)  London 1968
       Oblique Ionospheric Radiowave Propagation, AGARD Conference
          Proceedings (13), Technivision Services, Slough, England
          1969 (various papers)
       Propagation of Waves, David P. & Voge. J., Pergamon Press
          Oxford, England, 1969 (trans. 1966 Propagation des Ondes)
       Interim Method for Estimating Sky Wave Field Strength and Transmission
          Loss at Frequecies between the Approximate Limits of 2 and 30 MHz.
          CCIR - Report 252-2, New Delhi 1970
       The Teleprinter Handbook, Radio Society of Great Britain, London 1973
       Radio Wave Propagation, Armel Picquenard, (Philips Technical
          Library), MacMillan, London 1974

                                         14


       REFERENCES (continued)
       ----------------------
       Ground Wave Propagation Curves for Frequencies between 10 KHz and
          10 MHz, CCIR - Recommendation 368-2 Geneva 1974
       Bandwidth, Signal-to-Noise Ratio and Fading Allowances in Complete
          Systems, CCIR - Recommendation 339-5 Kyoto 1978
       On the Propagation of Short Waves over Long Distances -- Predictions
          and Observations, Hortenbach K.J. & Rogler F., Telecommunication
          Journal 46/6 1979  p320-329
       Radio Propagation Handbook, Peter N. Saveskie, Tab Books (No. 1146),
          Blue Ridge Summit PA 1980
       HF Antennas for All Locations, L.A. Moxon, G6XN, Radio Society of
          Great Britain, London 1982
       Ionospheric Radio Waves, Davies K., Blaisdell/Ginn, Waltham MA. 1969
       The Shortwave Propagation Handbook, George Jacobs and Theodore
          J. Cohen, CQ Publishing, Inc., Hicksville NY 1982
       MINIMUF: A Simplified MUF-Prediction Program for Microcomputers
          R.B. Rose, QST, Dec. 1982, ARRL, Newington CT
       Planning & Engineering of Short Wave Links, Braun G. Siemens/Wiley
          London, 1986
       Ionospheric Radio Propagation Model and Predictions, Rush C.M.
          IEEE Trans. on Antennas & Propagation AP-34 (9) Sept 86  p1163-70
       Radiowave Propagation,  ed. Hall M.P.M  &  Barclay L.W.,  Peter
          Peregrinus Ltd. (IEE) London, 1989 (various papers)
       Ionospheric Radio, Kenneth Davies, Peter Peregrinus Ltd. (IEE)
          London 1990
       The Ionosphere: Communications, Surveillance and Direction Finding,
          McNamara L.F., Krieger Publ., Malabar FL 1991
       Radio Auroras, Charlie Newton, G2FKZ, RSGB, London 1991
       ELNEC, (Program) Roy W. Lewallen, W7EL, Beaverton OR 1991
       MINIPROP PLUS, (Program and Manual) Sheldon C. Shallon, W6EL
          Software, Los Angeles, CA 1992
       HF Communications, Science and Technology,  John M. Goodman
          Van Nostrand Reinhold, New York 1992.
       ARRL Handbook and ARRL Antenna Handbook, ARRL, Newington CT
       Propagation, R.R.Brown NM7M, WorldRadio  May 1994, Sacramento CA
       HF Channel Simulator Tests of Clover, Peter Reynolds, KE4BAD
          QEX, Dec. 1994, ARRL, Newington CT
       The New Shortwave Propagation Handbook, Jacobs G.(W3ASK), Cohen T.J.
          (N4XX) & Rose R.B. (K6GKU), CQ Communications Inc. Hicksville NY
          1995 (extensive update of 1982 publication.)
       Radio System Design for Telecommunications, Freeman, R.L., John Wiley
          and Sons, NYC 1997

                    -----------oooooOOOooooo------------


      While no software support is offered for this 'FREEWARE' program,
       technical questions and comments will be welcomed by the author,
         Crawford MacKeand, WA3ZKZ, VP8CMY, at the mailing address of
             Tyndar Press, P.O. Box 236 Montchanin DE 19710, USA

           73 and enjoy using SNAP. Thanks for your interest and support.

             Crawford MacKeand WA3ZKZ, VP8CMY, ex-G4ARR  20 Aug 2001


                                     END OF FILE

                                         15