Catch Me If U
Can !! on “SSTV” A
Experiment worth trying with a PC and a HF rig Hi Everybody ! This is VU2UKR. I would like to share a small experiment that will help you to get
start sending and receiving colour pictures via Ham Radio using Slow Scan Tele Vision and
introduce you to this fascinating mode, so
get a taste of it and above all enjoy. I
started fancying “SSTV” ever since I
got a Email from a YL Ham operator from Brazil
in 1998, asking me if I operate on SSTV… to get a contact with India on
this mode ! I was very curious to go on the new mode, sent back a reply asking for more info
on SSTV, that YL “PT2TF” sent me some hyperlinks to help me catch the race
on the WEB. Since then when ever on the
NET, I search for “SSTV”. That was
the beginning….!!! In Simple words it’s the Exchange of “still” Pictures using Amateur Radio and a Personal computer
with sound card. A picture [ File like BMP, JPG ] in your Personal Computer is
scanned line by line by a computer program and converted to corresponding Audio
tones with respect to the color patterns and sending it over Radio as a RF signal. The receiving station on the other end converts the RF signals
to Audio tones and sends it to the Personal computer and the Program
loaded in the personal computer decodes the Audio tones and reconverts it
to Picture. This mode is simply great because you are not only able to
Communicate or send and receive pictures
but you can see the other operator when he/she sends his/her photograph
respectively. You can see pictures
of Earth as seen from the Space station MIR via SSTV, as the
cosmonauts who are HAMs use this mode to send and receive pictures. Usually they
send pictures of their control room of
the spacecraft, or connect the
spacecraft’s front camera to SSTV. Usually they operate on VHF/UHF
frequencies. Isn’t it interesting,
sitting at home and downloading pictures from a
spacecraft. All you need is a a)
Transceiver [ Homemade or Commercial ] b)
Computer - Preferably Pentium series
with Sound Card ·
CPU,
80486-DX/2/66 or Pentium preferred. ·
RAM, 8mb minimum. ·
SOUND CARD,
16-bit + MICrophone +Software
[ to encode & decode pictures] ·
VIDEO, Resolution
at 640*480 res. Or higher. ·
if “Dil Mange “ More then,
the more power your PC has, the better it will be! c)
A 32
“BIT” Patience J !!!! For
this experiment, No special hardware or
interface required. There are several simple ways to get setup for slow scan TV,
what I’m describing here is the VERY simplest, which use your computer and
transceiver with no Physical Interface
[ that I ‘m currently using ]. There are many other ways to do it…using OP-AMP interface. The shareware software required for SSTV can be downloaded from the Internet site viz., http://www.mscan.com What you need in your PC:- 1) SSTV Software 2) A Picture file to transmit [ say shack photograph ] [ BMP,
JPG, PIC…etc ] 3) Soundcard with
Speaker + Mic ready Frequencies :- SSTV
is always operated in the SSB segments of the HF bands. The SSTV calling
frequencies are 14.230 MHz, 21.340 MHz,
28.680MHz. The basics of SSTV Receive
:- Load SSTV Program. Tune Transceiver to SSTV
signal, SSB mode . Connect an external
speaker from your RIG, preferably use
the small headphone module,
removed from a scrap stereo
headphone. Place the Mic [ Condenser Mic ] in front of the Head
phone module. If the RX signal is strong then the SSTV program starts decoding
the picture automatically, else you can force it to decode manually. The most common SSTV modes are "Martin
1" and "Scotty 1", and you will hear SSTV users announce the
transmission mode before they transmit. Most software now automatically
recognizes the correct mode. Some of the software’s are viz., Mscan, MultiMode, W95SSTV, FTV, EZSSTV,
Chromapix etc ., Another way is to directly connect the “line out” of the
RIG to “Line in” of the sound card.
Sometimes the line out of the rig might not be sufficient for the SSTV
program to decode in that case additional
small AMP is required. [ I have not tested ]. A little patience is required till you get your first
picture on to your system, once you master the Magic then you will be rewarded.
When I started this experiment I tried to decode more than 50 sstv transmission, but the result was just a CLEAR
PICTURE of COLOUR GRAINS !! HI ! . Thanks to my XYL for
all encouragement , support and for her patience … watching me download, screens
full of color GRAINS for hours and
hours !! The basics of SSTV Transmit :- Load
the SSTV program. Select
the picture to send. Set
rig to SSB mode. Click
the transmit button. Once the
transmit button is pressed the PC Speaker turns on and starts squeaking
using different tones. The picture on the screen is scanned line by line and
converted to Audible tones respectively.
The Microphone is placed before the
PC speaker, [ Instead of PC
Speaker here I used Big headphones connected to PC to avoid feedback tone
]. Keep the MIC of the Rig in front of
the Speaker or headphones connected to
the PC . If you have a VOX [ Voice
operated Switch ] facility then switch
it on or else press PTT. Usually it takes about One minute and a half to send a picture. The
pictures are transmitted via Audio tones (1200-2300 Hz) over the air. My first attempt to this mode was sending a Picture via
SSTV to OM Karan VU3GTF, who at the
time was not ready for operating in this mode, so I asked him to receive the
Tones I sent and record it on a Audio Tape. Then He retransmitted it to me on SSB mode, so as to simulate SSTV station from his end, to my surprise I
could decode the audio tones that were recorded at his end, and got back the picture I send earlier. As things got hot
and results were encouraging OM
Raman VU3DJQ also joined me in the experiments and together we made things work better,
on 3rd Dec 2000, It was a great day for me as I had got my first DX on SSTV a station
EU6TV from BELARUS in Europe . The experiment was carried out using the following :-
Here
are the snapshots that were transmitted and received . For a Homebrewer this mode may be of quite good use as
one can exchange Circuits diagrams, schematics, application data over the Air. There are a lot of choices as to the selection of which SSTV
system to start with. The SSTV hams are usually very willing to help other
interested HAMS, SWLs or help you get started in slow scan. Interface:- With a little bit of hardware interface using OP-AMP ( IC741 or TL071
or TL084 ) one will be able to get
extremely high quality pictures. HAMCOMM
( A Simple interface software for RTTY and CW transceiving ) The same
hardware circuit will also run several of the SSTV software. If you don’t have an Amateur Wireless licence, then you can
receive the pictures exchanged by other
HAMs, just as Short wave listening. Hope that this fascinating mode of transceiving Pictures
finds a place in every VU HAMs shack.
There are many other modes relating your PC + Sound Card and Amateur Radio
like the PSK31, Hellscriber,
RTTY, receive Weather FAX from
satellites etc., Why wait , join the SSTV gang, and SSTV operators, just as
other operators will be pleased to give a helping hand to setup your station. I
would be pleased to help anyone to get on this new mode. A Homemade Radio Transceiver and a PC is just sufficient for SSTV to begin with. Catch
me “on SSTV “ if you can ! 73’s Sunil.U.K de VU2UKR ex: M / VU2UKR
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