7/30/2019 SSTV SELL

1/15

A MODERN GUIDETO

SLOW SCAN TELEVISION

ANDDATA MODE

RECEPTION/TRANSMISSION

BRIAN SMITH , G0IER

S.S.T.V. RECEIVED ON 80 METRES FROM G0AZXIN YORKSHIRE TO G0IER IN WILTSHIRE.

A BEGINNERS GUIDEINCLUDING

PICTURES AND DIAGRAMSWITH SOFTWARE FOR SSTV , WEFAX , RTTY , CW , AND OTHER

DATA MODE RECEPTION / TRANSMISSION.

1997

A guide to Slow Scan Television and Data mode reception / transmission.

1

7/30/2019 SSTV SELL

2/15

First of all , may I say that data mode transmission and reception has been arounda lot longer than digital electronics , and longer than me as well !

There are many ways to send and receive data modes , using both analogue and digitalelectronic circuitry. I would like to concentrate on a modern method of sending andreceiving data modes. This will involve the use of the IBM compatible personal

computer .

Although we will be taking a closer look at slow scan television , the equipment wewill be discussing in this article is good for all the following forms of data modereception and / or transmission .

1. RTTY. 2. WEFAX. 3. CW. 4. PAKET. 5. SSTV

Here are some brief details on these modes.1 - RTTY. This stands for Radio Teleprinter communication. Under the RTTYumbrella are Baudot , Amtor and ASCII modes. Amateur RTTY signals use a baudotrate of 45.5 . Commercial RTTY uses 50 , 75 and 100 baud . Amateur RTTY can befound on 14.090 Megahetz. Commercial RTTY can be found above the 40 metreamateur band.

Much of the commercial RTTY these days is sent in coded form , and will not makemuch sense even when correctly resolved. However , occasionally a news agency can

be found sending plain text RTTY and getting international news before the BBC canbe fun ! Amtor is a form of RTTY but with computerized error checking thrown in.

2 - WEFAX. This stands for weather facsimile transmissions. These weather picturesoriginate from satellites. They are re - broadcast on the H.F. bands. Weather maps can

be constructed from these images. Try 3.853 , 7.878 and10.248 Mhz when looking for weather map facsimilies.

3 - Morse Code. How can I include morse code in a discussion on data modes ? !Well , c.w. can be treated as data and decoded by computers quite easily. C.W.essentially consists of an ON / OFF state. If we can time these on / off states thensense and intelligibility can be deduced. This is known as morse code !

4 - PAKET. Paket radio has been around for quite a few years now. It is a fantasticsource of information and data. It is the amateur radio version of the Internet.The paket system is text based. However , computer files can be sent and received

by using compression and extended ascii codes.

The equipment we discuss tonite is not suitable for transmitting paket . However ,paket data can be received using a software utility program that comes with theHAMCOM RTTY software.

5 -SSTV. This stands for slow scan television. Slow Scan television has been aroundsince 1958 at least. Early SSTV was monochrome or black and white and received on

2

7/30/2019 SSTV SELL

3/15

high persistance c.r.t s or cathode ray tubes. An early sstv picture took about eightseconds to send. Modern SSTV takes longer , about a hundred seconds per picture.

However high resolution pictures with up to sixteen million different colours availablecan be sent and received using modern SSTV formats. Results can be of photographquality in good conditions as we shall see later.

SSTV signals can be found on 3.730 and 14.230 Megahertz

Slow scan television is a narrow bandwidth image transmission system that usesaudio tones to convey the video information. This makes SSTV suitable for use on theH.F. and VHF bands.

Using the methods described in this article SSTV can be sent and received with bothFM and SSB modes.

In the early days of SSTV a transmission may have consisted of a white backgroundand a callsign in black lettering. The audio tones used for early SSTV picturesconsisted of a 30 millisecond pulse at 1200 Hertz to signal the start of a new image.Scan lines were seperated by a 5 millisecond pulse at 1200 Hertz . A total of 120 scanlines completed one picture.

The video swing from black to white was represented by tones of 1500 hertz and 2300hertz respectively. Total bandwidth 1100 hertz or 1.1 kilohertz. The tones between1500 and 2300 Hertz are availble for grey scale or colour information .

The advent of digital electronics and the home computer has revolutionisedSSTV. High resolution colour pictures and photographs can now be sent with ease.

Today , the most common SSTV modes used are known as Martin and Scottie modes.The Martin sstv mode was developed by Martin Emmerson G3OQD. The Scottie sstvmode was developed by Ed Murphy GM3BSC. These newer modes use separatescans for Red, Green, and Blue picture components. Both modes allow the user tosend and receive high resolution colour pictures via a computer , a radio , and aninterface to connect the radio to the computer.

EQUIPMENT NEEDED FOR SSTV AND DATA MODE RECEPTION.

Three vital pieces of equipment are required for SSTV reception.....1. A Computer.2. A Comparator Interface.3.A Radio Receiver or transceiver

1. THE COMPUTOR

An IBM PC Compatible 486 is where I began. A 386 should be fine , as well. Theability to handle 256 colours or better is important to enjoy SSTV at its best. A VGAmontior is essential , and SVGA preferable for best results.

3

7/30/2019 SSTV SELL

4/15

The computer is attached to the comparator via a serial port. The serial port uses aprotocol know as RS 232 to send and receive data as a stream of binary zeroes andones . The serial port is also known as a COM port. There are usually two serial orCOM ports to be found on the rear of modern IBM PC compatible computer.

These COM ports are designated as COM 1 and COM 2. COM 1 is normally foundon the computer rear panel as a nine way male D type connector. COM 1 is usuallytaken up by the computer mouse. Hence the term serial mouse.

COM 2 is usually the spare serial port that equipment such as the SSTV comparatorinterface is plugged into. COM 2 will generally be found as a 25 way male D typeconnector on the computer rear panel. COM 2 can get a lot of use. As well as mycomparator interface , I also use COM 2 for my PAKET TNC .

A COM port patch lead will save a lot of wear and tear on the computer rear panel.It also makes access to COM 2 much easier as the patch lead can be bought tothe front of the PC. To build a COM port patch lead one male and one female 25 wayconnector will be required. Connect together pins 2 , 3 , 4 , 5 , 6 , 7 , 8 , 20 and 22.Use 8 core screened cable and connect the screen to pin 7 , the ground pin.

This will provide a full duplex patch lead suitable for any and all serial portapplications. Unless you are a whizz kid at computer programming , suitable softwarewill have to be installed onto the computer to send and receive the data modesdiscussed.

Once the software is installed it will ned to know which COM port to listen to !Generally COM 1 is stored at address 03F8 Hex and is serviced by IRQ 4 and COM 2is at address 02F8 Hex and serviced by IRQ 3. It is worth noting these details as somedata software may require these details before functioning correctly.

SOFTWARE

As well as suitable hardware , suitable software will need to be installed onto thecomputer to persuade it to decipher the strange signals. Three well known shareware

packages are JVFAX , DL4SAW and HAMCOM

1 - JVFAX. This software can receive weather facsimilie transmissions . JVFAX willalso transmit and receive SSTV pictures. It has the advantage of coping with 16 coloronly displays.

2 - DL4SAW. DL4SAW is a dedicated SSTV program that has a user - friendlyinterface. It can send and receive sstv pictures in many different modes. The Defaultmode for sending and receiving SSTV is M1 Colour Martin. This is the mode

DL4SAW first selects.

4

7/30/2019 SSTV SELL

5/15

3 - HAMCOM. This software will transmit and receive RTTY , AMTOR and C.W.signals . HAMCOM comes complete with a small utility file that can be used toreceive Paket transmissions , but sadly is not able to transmit paket clusters. This

paket receive utility file is known as PKTMN12.EXE. ( Paket Monitor ver 1.2 )

Once JVFAX or DL4SAW is installed onto the computer a one off tuning process

has to be undertaken. This is known as slant correction. It tunes the software timing tothe computers hardware timing for accurate picture reception. This applies to bothJVFAX and DL4SAW software. Until slant correction has been completed pictureswill be received slanted no matter how well they are tuned in.

PICTURE SOURCES

If transmitting SSTV a good source of picture material is required. WindowsPainbrush can be used to create coloured backdrops and large size text can then beadded . Simple test card pictures can be created in paintbrush.

Computer picture files come in a variety of shapes and sizes. Filename extensionswhich indicate a picture file include.....BMP ( Bitmaps ).GIF ( Graphic Information Files ).JPG ( Jpeg compressed picture format. ).PCX.PIC.CLP ( Clipart)

.IMG

.TIFAny picture file is fair game for the SSTV treatment. A good source of graphic filesare computer magazine coverdisks. These coverdisks are free with the magazine andand often contain a variety of graphic files which come royalty free.

Home and shack operator photographs are a great source of material for SSTVpictures. A picture scanner will be needed to digitise photos , or the loan of one , andflat bed scanners are now available under 150 pounds.

A digital camera would be the perfect solution but they do not come cheap !

PICTURE MANIPULATIONPicture manipulation is important for good sstv pictures. The sstv operator will need toadd text , such as callsign , name and location , to the pictures prior to transmission.Adjustments to picture size , colour content and contrast may also be required.

Once again lots of software is available to manipulate graphic files.

The all time ideal image manipulation package has to be Paint Shop Pro for windows.

Shareware versions of PSP can usually be found in the utility section of coverdisks.Paint shop pro can be used to add text and edit pictures. It handles thirty - fivedifferent picture file formats. Once a picture is ready it can be saved as a bitmapfor use with sstv software.

5

7/30/2019 SSTV SELL

6/15

Once the computer has had suitable software installed , the next step ishow to get it connected to the radio ! This is where the comparator interfacecomes in.

2. THE COMPARATOR INTERFACE.

The comparator interface is connected between the computer serial port and the radio.being used to send or receive data. It is a simple electronic circuit which conditions thereceived data signal by changing the signal level to a voltage level suitable for theRS232 port.

The comparator interface draws its power from the serial port. Diodes attached to thecomparator op - amp voltage rails connect to positive and negative signals available onthe RS 232 port.

Therefore no external power source is needed to run the comparator interface.The input signal to the comparator interface comes via the receiver headphone orextension speaker socket. Comparators can be bought quite cheaply at rallies , or fromthe classifieds in the back of radio mags. It makes a good homebrew project , beingvery simple.

There are certain sstv software packages available that utilise multi-media sound cardsin lieu of a comparator , but I have no knowledge of the success or otherwise of thistechnique.

It is worth remembering that one comparator can be used for resolving all the datamodes discussed in this article , providing suitable software is installed. Morecomparator interface details can be found in part two of this document .

So once a suitable PC and interface have been arranged all that is left to do is toconnect the equipment to the radio, which brings me to the final part of this article.

3. THE RECEIVER / TRANSCEIVER

If data reception only is required things could not be easier. Simply plug thecomparator interface into the headphone socket or extension speaker socket.A general coverage receiver with ssb capability should be fine for H.F. workor a scanner with FM mode for VHF work.

Spot frequencies to begin searching for SSTV are 3.730 Mhz ( 80 mts ) and14.230 Mhz ( 20 metre band ) A regular sstv net has been appearing around3.780 Mhz in the mornings . Local sstv using two metres FM can sometimes

be found around 144.450 Mhz .

In order to transceive sstv some consideration must be give in how to connectthe interface to the transceiver. IC 706 users are lucky - the 13 pin accesory

6

7/30/2019 SSTV SELL

7/15

socket on the rear panel has all the required connections to transceive . Other rigs mayneed to utilise the mic socket and / or extensioin speaker socket as required.

A total of four connections will be required to connect the comparator to theradio for transceiving sstv and these are ......1-Ground

2-PTT line3-Mike line4.RX audio lineIcom 706 owners will find these connections on pins 2 , 3 , 11 and 12 respectively onthe rear panel accessory socket. The hardest part will be sourcing a thirteen pinDIN plug.

SSTV fun can be had using two meters F.M. Simply find a suitable data modefrequency and a pal to swop pictures with.

IC2E owners may like to know that transceiving SSTV can be achieved by attaching a33 kilohm resistor between the comparator interface PTT line and the MIC line.

Finally , this article includes diagrams of receive and transceive comparators.Shareware versions of HAMCOM , JVFAX , and DL4SAW , on two floppy diskscome with this article.

EASYSLOW SCAN TELEVISION !

7

7/30/2019 SSTV SELL

8/15

A BEGINNERS GUIDEINCLUDING

PICTURES AND DIAGRAMS

BRIAN SMITH G0IER

1997

EASY SLOW SCAN TELEVISION !

Brian Smith G0IER , 48 , Colchester Close , Swindon , Wiltshire , SN5 8AG

A guide to sending and receiving slow scan television pictures using equipment found in the modernshack.

Here is how I got started sending and receiving S.S.T.V. pictures over the air . There are manydiverse circuits and much equipment available for those interested in Data decoding , and Slow ScanTelevision is no exception to this rule.

This article concentrates on a cheap and easy way to enjoy S.S.T.V. reception / transmission and isnot aimed at the technically minded. All that is needed to enjoy any type of data mode reception ortransmission , is a computer , a receiver or transceiver , and an interface unit !

The interface unit connects the radio to the P.C. as shown below.....

8

7/30/2019 SSTV SELL

9/15

Lots of shacks have a Personal Computer as part of the station equipment these days , so for manyamateurs or short wave listeners , all that will be needed to start enjoyingS.S.T.V. reception / transmission is the interface unit that links the P.C. to the shack radio , andsome suitable software.

The software is freely available as shareware , which means try before you buy ! You cannot getcheaper than that !

With a suitable computer and interface unit , pictures of almost photograph quality can be sent andreceived via the amateur bands. It makes fascinating viewing .

An S.S.T.V picture takes about one hundred seconds to build up from start to finish , when using theprotocol known as M1 ( colour Martin ) , which is the default standard used.

My shack computer is a 486 SX , capable of supporting two hundred and fifty six ( 256 ) colours ingraphics mode . The minimum requirement for enjoying S.S.T.V. picture reception that I wouldrecommend would be a 386 computer with sixteen colour VGA graphic support running the famousJVFAX software.

Two hundred and fifty six colour graphic support is a fairly common standard thesedays though , and offers much better colour content when receiving SSTV pictures. In fact , manyP.C.s can support sixteen million colours without a problem !

For those with 256 colour graphic support or better I recommend the DL4SAW slow scan softwarepackage. This shareware is very easy to set up and is user friendly. It is excellent for transmitting aswell as receiving S.S.T.V. pictures. I do appreciate many others will be enjoying SSTV utilising awide range of computers , equipment , and methods.

The method described in this article has two things going for it though - its easy and itsfun ! The first obstacle to overcome was how to connect the P.C. to the radio. I decided to use the

cheapest , easiest and quickest method - with excellent results.

The method I used to hook up the radio to the computer is known as the Comparator method.The comparator is a small electronic circuit that connects between the radio and the

9

7/30/2019 SSTV SELL

10/15

P.C. The comparator has a signal input which is fed from the radio headphone or extension speakersocket .

Various designs of comparator cicuit have been published and a typical receive only circuit is shownbelow

In this circuit I have uprated the supply smoothing capacitors and used a twenty five way female D

type connector for connection to the serial port COM 2.

The comparator output is fed into the computer serial port , usually described as COM 1 or COM 2 .

Power for the comparator circuit is provided by the PC serial port , thanks to the comparatordiodes , which act as rectifiers. The COM ports allows data to enter or leave the computer as aseries of binary digits which pass into the computers memory one after the other in a serial fashion.Hence the term serial port !

There are usually one or two COM ports found on the rear panel of the P.C. They come in theform of nine way or twenty five way male D type connectors . One COM port is often used to

interface the computer mouse to the P.C.

Most modern computers have a nine way D type male COM 1 , that is utilised by a serial mouse ,and a twenty five way D type male COM 2 which is where the comparator would go. Thecomparator interface can be obtained comercially at a reasonable cost if home brewing is not desired.

Adverts for these comparators can usually be found in Practical Wireless and SWM . Check thesmall ads ! The comparator interface does make a good beginners project however , especially thereceive only version of the comparator.

I built my first comparator onto veroboard with a D type connector soldered directly onto theveroboard. The PCB is then supported by the connector which plugs directly into the computer serial

port.

10

7/30/2019 SSTV SELL

11/15

In order to fit the D type connector to the veroboard I had to remove the surplus pins , as the pitchbetween pins does not match the veroboard hole pitch. The layout for the circuit is shown below.The veroboard track connections are also shown

The input to the comparator interface can be taken from any audio output device that the shack radiooffers. This could be the headphone or extension speaker socket. I used the extension speaker

socket in a rather novel way. A pair of personal stereo mini speakers was purchased at a rally for acouple of pounds brand new. The rear panel of one speaker was removed.

11

7/30/2019 SSTV SELL

12/15

I fitted a small volume control potentiometer with a value of 100 ohms , in series with the extensionspeaker. The comparator signal input was then taken from the hot side of the volume control .This then allowed me to adjust the audible volume from the extension speaker without affecting thesignal input level to the comparator interface.

The reason for this is I needed to hear the data signal in order to tune it in , but once the data is beingsuccessfully decoded I was able to turn down the audio , which does not sound very pleasant ! This

idea is illustrated in the diagram below.

After succesfully receiving S.S.T.V. I wanted to transmit as well , so a second , transceive version ,of the comparator interface was built.

The receive section of the circuit remains the same , but a Push To Talk (P.T.T.) line controltransistor is added. A signal path from the P.C. to the microphone line is also required in order totransmit S.S.T.V pictures as well as receive them.

The circuit diagram for the transceive comparator is shown below

12

7/30/2019 SSTV SELL

13/15

The P.T.T. control line will be activated by the computer when the transmit function is selected inthe software programme.

The audio signal from the P.C. is filtered by resistors R 3 / 4 / 5 and capacitors C4 and 5The signal level to the microphone line is varied by potentiometer VR 1.

I connected my transceive interface to my ICOM 706 radio via the 13 pin DIN type accessory socket

on the rear panel of the rig. This socket has all the required signal input / outputs , which are RXaudio , Ground , Microphone input and P.T.T. line. These connections should be available on almostany transceiver with an eight pin microphone socket. Refer to your rig manual for pin out details.

For those readers with an ICOM 706 the hook - up details for the rear panel accesory socket aregiven below............

Pin 12 = (RX. AF. ) Pin 2 = ( GND )Pin 3 = ( PTT ) Pin 11 = ( Mic. input )

IC2E Owners can transceive correctly by connecting a 33 kilohm resistor between the comparator

interface PTT line and MIC line. A diagram is included in the Appendix.

Once the interface was built and installed the next hurdle was what software to use. There are manySSTV programs available as shareware , but I found the DL4SAW software package an absolute joyto use and have stuck with it ever since.

The DL4SAW software comes as a compressed file. The title of this file is GSHSTV12 . .ZIP , andit has to be decompressed and installed onto the computer hard drive before being used. A fileknown as PKUNZIP.EXE , or the excellent Windows based WinZip program will do all thedecompression of the software. An actual screen shots of S.S.T.V in action is shown below.Although reproduced here in monochrome in reality the pictures can be sent and received in colour.

13

7/30/2019 SSTV SELL

14/15

The screenshot shows the DL4SAW S.S.T.V. software with a received on air picture in the righthand window and a picture loaded into the left hand window ready to transmit.

Pictures can be swopped back and fore between the transmit and receive windows , so a receivedpicture can be retransmitted to show how it was received. Text can be added to pictures prior totransmission , and many other refinements are available with DL4SAW SSTV convertor.

I would like to end this article with some hints for sending and receiving S.S.T.V. pictures.The S.S.T.V. frequencies are presently :

80 Metres : 3. 730 MHZ 20 Metres : 14.230 MHZA morning net can be found around 3.780 and local SSTV can be found on 2 metres FM around144.450 Mhz

Many S.S.T.V. ops who transmit seem to forget the simple etiquette involved. The R.S.G.B.amateur radio operating manual suggests an identity call should be made before and after S.S.T.V.transmissions , both for the benefit of listeners and to comply with licence conditions.

I urge potential S.S.T.V. users to comply with this ! Also , as S.S.T.V. gains in popularity sofrequency space gets more and more squeezed. Be patient , wait for your turn , and do notantagonise single sideband operators who are nearby working non - SSTV.That said , let me end by saying Good Luck , and Have Fun !

APPENDIX

The first diagram below shows details of a COM port patch lead - this will save wear and tear on thecomputer rear panel and also makes the COM port more accessible if other equipment is used on this

port , such as paket TNC controllers and so on.

14

7/30/2019 SSTV SELL

15/15

The second diagram shows connection details for those who wish to transceive with Icom IC2E stylehand held transceivers.

Brian Smith G0IER. 1997

15