		Questions + Answers
		-------------------
		
	--- Tired of those same old boring ham radio ---
	--- club meetings?  Why not give a talk about ---
	--- Slow Scan TV?  A Question + Answer sheet ---
	--- would make a great handout. ---


	       
Q: Why send pictures over the radio?

A: The ancient Chinese proverb, "A picture is worth a thousand 
   words," is just as true today as it was thousands of years 
   ago.  Vision is our highest bandwidth sense and the primary 
   source of information about the world around us.  Material 
   is easier to understand and more enjoyable when images 
   accompany verbal descriptions.

   Would you watch television with your eyes closed?  Do you
   look the other way when talking to someone in person?  Why 
   not make your ham radio contacts more interesting by 
   including pictures?

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Q: How much does it cost to get started?

A: If you already have a voice transceiver and a computer, you 
   can send and receive pictures at zero cost or very close to 
   it. If you're impatient, skip to the last question for details.

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Q: How does SSTV differ from ATV?

A: There are basically two methods used to send pictures over 
   ham radio.  Fast Scan TV is very similar to broadcast TV: 
   full motion color images.  This requires a few megahertz of 
   bandwidth so it is used only on UHF.  A single transmission 
   is wider than the entire 2 meter ham band.

   The other method is Slow Scan TV: still images sent through 
   voice transceivers over a period of a few seconds to a couple 
   minutes.  Early pictures were low resolution black and white.  
   Now nearly all images are higher resolution color.

   You'd expect the term Amateur Television to apply to both Fast 
   Scan and Slow Scan but it generally means only Fast Scan TV.

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Q: What kinds of pictures are sent?

A: Reviewing pictures saved during the last few weeks I found: 
   Hams in their shacks, lots of pet dogs, a frog, kangaroo, 
   astronauts in the Space Shuttle (SSTV has been transmitted 
   from some missions!!!), bridges, birds, Elvis Presley, rock 
   formations, an old fashioned microphone wearing a Santa Claus 
   hat, antique cars, flowers, children, Jupiter, a cow, someone 
   playing bagpipes, many colorful butterflies, boats, and cartoon 
   characters with personalized messages.  Many SSTV'ers show off 
   their artistic abilities by sending pictures they made with 
   paint programs.  

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Q: Will future Space Shuttle (SAREX) missions transmit SSTV? 

A: A few years ago there were only several thousand people with 
   the facilities to receive SSTV images.  The effort to transmit 
   SSTV from a Space Shuttle benefitted very few people.
   Today, anyone with a VHF scanner, a computer, and a few cheap 
   parts can receive full color SSTV images.   Now, millions of 
   people could benefit from these transmissions.  

   Contact the ARRL and SAREX committee members with your thoughts 
   on this topic.   Tell them how you can help by donating 
   equipment, educating your local club members about SSTV,
   or setting up a Space Shuttle SSTV demonstration at a school 
   or shopping mall.

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Q: How is the image quality?

A: Pasokon TV now offers images up to 640 x 480 pixels with
   16 million colors.  Other systems are generally limited 
   to 240 lines of 320 or 256 pixels.

   Remember that SSTV uses analog transmission so the the
   received image will not be identical to the the transmitted
   image even if there is no noise.  The older modes, such
   as Scottie S1 or Martin M1, are limited to 240 scan lines.
   For best results, use the new Pasokon TV high resolution
   (480 line) modes.

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Q: What frequencies are used?

A: Some countries are more restrictive, but in the U.S.A., SSTV 
   can be used anywhere voice is allowed.  Traditionally, 
   certain frequencies have been used as meeting frequencies: 

	3.845   3.857 
	7.171 
	14.230  14.233  
	21.340 
	28.680  
	145.5   MHz

   20 meters is generally your best bet for finding activity.  
   80 meters is also popular.

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Q: What class of ham license is required?

A: If you are allowed to transmit voice, you are allowed to 
   transmit SSTV on the same frequencies.  The one exception 
   is the Novice/Technician 10 meter segment.

   (This is for U.S.A.  Rules for other countries will vary.)

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Q: Are there any nets?

A: Saturdays at 15:00 and 18:00 UTC on 14.230 MHz.

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Q: Are there SSTV contests?

A: There are the usual types of contests were participants try
   to make the maximum number of contacts in a certain amount 
   of time.

   There are also contests for the best pictures.  The theme 
   is often the next holiday, such as Holloween or Christmas.  
   
   There are different categories for natural and computer 
   generated images.

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Q: Is SSTV new or has it been around for a while?

A: Amateur SSTV has been around since 1958.  

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Q: Why do the magazines and handbooks ignore this facsinating 
   mode?

A: There were many articles in the early days when most people 
   homebrewed their own equipment.  In the 1970's and 1980's 
   most people bought commercial equipment and exchanged pictures.  
   Few people could afford the expensive equipment and there 
   really wasn't much to write about. 

   In the last couple years, many new low cost SSTV systems have 
   become available and thousands of hams have discovered the 
   fun of SSTV despite the difficulty in finding information.  
   Ham radio magazines in Europe and Japan constantly have 
   articles on SSTV.  I have no idea why the American publishers 
   continue to ignore it.

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Q: How has equipment changed over the years?

A: SSTV started out with surplus radar display tubes with very 
   long persistence ("P7") phosphors.  This allowed an image to 
   be painted on the screen over a period of a few seconds.

   When memory chips became affordable, scan converters became 
   feasible.  Scan converters translate one TV standard to 
   another.  In this case the scan converter takes video from a 
   TV camera (e.g. camcorder) and translates it for SSTV 
   transmission.  In the other direction, it stores an SSTV 
   image in memory and allows it to be displayed on an ordinary 
   TV set.

   The latest trend is to use a personal computer, software, 
   and an interface attached to your transceiver.  This is much 
   less expensive and much more flexible.  

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Q: What kinds of commercial equipment are available?

A: There are basically two types: Dedicated scan converters 
   and PC-based systems.  The legendary Robot 1200C scan 
   converter was discontinued in 1992 but other new products 
   such as the TSC-70 have moved in.

   PC-based SSTV systems abound: Pasokon TV, SSTV Explorer, 
   ViewPort VGA, PC SSTV 5, and MultiScan all have their own 
   hardware interface that connects the computer to a transceiver.  
   Some Multi-mode TNC's can handle SSTV with optional software.  
   You can even use a Sound Blaster with the Slow Scan II 
   software.

   Your best source of information for all the latest product
   information is the World Wide Web:

	http://www.ultranet.com/~sstv

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Q: What are trade-offs between special purpose scan converters 
   and PC-based systems? 

A: Dedicated scan converters offer some advantages:  You plug 
   in the cables, turn on the power, and they work.  You don't 
   need a computer.  They are expensive.  

   Most people with scan converters use a computer anyhow, 
   to store images, so why not use a low cost interface and 
   let the computer do most of the work?  This is also more 
   flexible, new features are distributed by floppy disk 
   instead of hardware changes.  There are two major 
   disadvantages.  First, none of the current systems allow 
   you to run SSTV concurrently with other applications.  
   Second, there are occasional conflicts or incompatibilities 
   when adding new hardware and software to a computer system.

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Q: Where do I plug in my TV camera?

A: The dedicated scan converters all have video input but 
   none of the current PC-based systems do.  Capturing an 
   image from a TV camera, such as a camcorder, requires an 
   extra device called a frame grabber.  Of course, frame 
   grabbers have many other uses besides SSTV and new models 
   are continually being introduced by many manufacturers.

   The bad news is that frame grabbers require a fair amount 
   of high speed specialized circuitry and memory.  The good 
   news is that prices are tumbling due to new technology 
   and increased competition.  The same product that had a 
   list price of $600 a couple years ago, can now be found 
   for about $300.  Innovative new products, such as "John's 
   Frame Grabber," demonstrated at the Dayton Hamvention, 
   will provide better image quality at even lower prices.  

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Q: What should I look out for when buying new or used equipment?

A: There are many transmission modes in use.  Make sure the 
   system can receive all the popular ones.  If you were to 
   pick up an old Robot 400 (black & white only) system at a 
   flea market, you'd be very dissapointed to find out no one 
   sends B&W pictures any more. 

   There is a wide variety in features, ease of use, 
   documentation, price, and so on.  Get on the air.  Talk 
   to people.  Ask what they are using and how they like it.
   Any one who has ever tried Pasokon TV will tell you it is 
   the best.

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Q: What plans are available for homebrewing?

A: Magazine articles in the last couple years:
    
	73 Amateur Radio Today -- August 1992
	QST -- January 1993
	QST -- January 1994 
	Radio Fun -- February 1995
     
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Q: Is SSTV software available for the Macintosh?  

A: No, so stop asking.  Someone, please tell me I'm wrong
   and I'll publish the details here.

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Q: Are there any handbooks or newsletters dedicated to SSTV?

A: There are only two modern SSTV handbooks:      
    
	Slow Scan Television Explained     
	by Mike Wooding G6IQM      
	(1992  --  ISBN 0-9513779-3-0)      
     
	SSTV HANDBOOK        
	The primary author is JA6OAC but the rest is 
	hard to decipher because it is in Japanese.)      
	(1994  --  ISBN 4-7898-1011-9 C3055 P4500E)  

   The 1995 ARRL Handbook also has a completely new and
   greatly expanded section on SSTV.

   The Internation Visual Communications Association (IVCA) 
   has a newsletter in addition to its nets, contests, 
   Dayton booth and other activities: 

	IVCA 
	P.O. Box 140336 
	Nashville, TN 37214  

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Q: Where can I get more information on this fascinating mode?

A: The best place to find the most complete, up to date 
   information about SSTV is on the World Wide Web:
   
	http://www.ultranet.com/~sstv

   Those without electronic access can send a large 
   self-addressed stamped envelope with postage for 3 ounces 
   (that's currently 32 + 23 + 23 = 78 cents in the U.S.) to: 

	John Langner  WB2OSZ 
	115 Stedman St.  #P
	Chelmsford, MA 01824-1823 
 
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Q: How can I get started with little or no investment?

A: Either dip into your junk box or take a few dollars to 
   your local Radio Shack store, and build the circuit below.  
   This circuit simply takes the received audio, amplifies 
   the signal, and sticks it into a status line of a serial 
   port.  Software measures the time between the zero 
   crossings to determine the frequency.  The software 
   converts these tones into images on the screen.

   The circuit shown here is the bare minimum.  

	

			    U1 - top view
		    (pins pointing away from you)                25    9
			notch on this end           J1    name   pin  pin
			and/or dot near pin 1             ----   ---  ---

			      +----U----+         +-----+
			      | 1     8 |    +----|--O  |  DTR   20    4
audio from     | |            |         |    |    |     |
receiver  -----| |---+--------| 2     7 |----+    |     |
	       | |   |        |         |         |     |
	    C1       |   +----| 3     6 |---------|--O  |  DSR    6    6
		     <   |    |         |         |     |
		      >  | +--| 4     5 |         |     |
		R1   <   | |  +---------+         |     |
		      >  | |                      |     |
		     <   | +----------------------|--O  |  RTS    4    7
		      >  |                        |     |
		     |   |                        |     |
audio ground --------+---+------------------------|--O  |  GND    7    5
						  +-----+


						Radio Shack
						part #           $
						-------        -----
	U1      741 or similar op amp           276-007         0.79
	R1      47K resistor                    271-1342        0.39
	C1      0.01 uF capacitor               272-131         0.49
	J1      DB25S                           276-1548        1.99
	    or  DB9S connector                  276-1538        1.29
	-       Shielded cable for audio         ?               ?


   There are many other minor variations on this theme using 
   diodes for reverse voltage protection, capacitors or power 
   filtering, and transformers for isolation.  If you already 
   have a HAMCOM, FAXCAP, SSC PC HF Facsimile, or AEA FAX 
   demodulator they will all work with some and maybe all the 
   software mentioned here.

   Next, find some free software such as E-Z SSTV version 3.  
   Here are some places to look:

	Internet ftp:
    
		ftp.ultranet.com:       /pub/sstv
		oak.oakland.edu:        /pub/hamradio/pc/digital/atv
		ftp.cs.buffalo.edu:     /pub/hamradio
		ftp.ucsd.edu:           /hamradio/sstv
     
	Telephone BBS:
    
		ARRL BBS                (203) 666 0578
		ATV today BBS           (319) 886 6020
		Compuserve, America On-line, GEnie, etc. have
		ham radio areas.
    
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