SLOW SCAN TV - Software MS-DOS per SSTV tramite Sound Blaster

[INFORADIO]

SLOW SCAN TV - Software MS-DOS per SSTV tramite Sound Blaster

Disponibile alla seguente pagina: http://www.forumradioamatori.it/download/download-dos/SSTV/SSTV.html


This program is designed to display 8 second BLACK & WHITE slow scan
pictures that you can copy off the ham radio bands. The frequencies
that you will normally find slow scan are:

3.845  MHZ
7.171  MHZ
14.230 MHZ
21.340 MHZ
28.680 MHZ

The most popular frequency is on 20 meters at 14.230 MHZ, with 14.233 MHZ
being used on weekends when there are too many on 14.230. The audio from
your reciever needs to be connected to the microphone input on the Sound
Blaster. I did the development on the Sound Blaster Pro, but I kept the
sample rate at 12 KHZ (the top speed for the Sound Blaster) so all Sound
Blasters could be used. It seems to give acceptable results at this speed,
however, a faster sample rate would give even better pictures. In a future
version, if there is interest, I may make a version with extra options
for the Pro version.

Copy the program to your hard disk (I would make a seperate subdirectory
called ss). You need all the BGI files for the program to run. Your
computer should have several meg of free space as the .VOC files will
take up about 100k for every 8 seconds of recording. Also you will want to
save some of your favorite pictures in .PCX files so you can recall them
later. The reason I chose .PCX format to save is that it generally takes
a lot less space than .VOC files. The display on your computer needs to
be a VGA display that will work in 640 x 480 - 256 color mode. Some
VGA cards do not have enough memory to do this. If it doesn't work on
your system, I need to know so I can make the necessary changes. When
reporting problems, please make sure to include as much information
about your computer system as possible, so I can be of help. To start the
program after it is loaded type "SS".

Once you have the audio connected, and a station ready to transmit, pressing
F2 will start the recieving process. The sound is stored in a disk file
named "temp.voc". This file is overwritten every time you press F2. You
will not see anything happen until you press ESC which should be pressed
as soon as the audio for the picture stops. The "temp.voc" file will be
a minimum of 100k in size for one 8 second period, so you will need to
make sure that you have at least 500k free on your hard disk where ss.exe
is loaded (several megabytes would be even better). You will learn after
using the program that it takes a little bit before it starts recording,
so you need to anticipate the start of the picture just a little.

If you anticipate too much, you can do a couple of different things:

1. Press ESC will stop the recording & start to display whatever there
   was to that point - Pressing ESC again will stop the display -
   Pressing F2 will restart the recording.

2. If, after you are displaying the picture, you see that the top of
   the picture is part way down on the screen,,pressing the space bar
   will make the rest of the picture restart from the top so you will
   see a complete frame.

Note: I know that it is pretty slow by not copying the picture to the
screen as it is comming in, but that can be changed in a future version.

Once you have a picture on the screen, if you Press F2 again you will
loose the one you have. Menu item F7 allows you to save the picture
as a .PCX file, or you can rename the "temp.voc" file to another name
so when you press F2 again, you do not loose the picture. I have, just
for the fun of it, looked at the .VOC file & edited them in VEDIT which
comes with the Sound Blaster.

Even though I wrote the program code for 8 second Black & White, I have
been able to recieve 36 second, 72 second, & SCOTTY 1 in Black & White.
A portion of the picture gets thrown away (you only see the left hand
upper corner) but, even I was quite suprised when I saw how well it did.

Help is built into the program and accessed by pressing F1. This will
give you a second menu of help items. Just press the F key that will give
you the information that you want.

Test images are built in, but, other than nice to look at, until there
is a send program written, are of little use.

The CONTRAST, SYNC, and BLACK can be adjusted if desired. This is left
over from my development stages & was left in. It may give you more
insight into how a Slow Scan picture works by playing with these. Once
you have recorded & have a "temp.voc" file, you can use this file under
the F7 option to redisplay as many times as you like using the SYNC,
CONTRAST, and BLACK. For those not familiar with Slow Scan, there are
many different type & modes. An excellant discussion is in the January
1993 issue of QST.