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? Why not make your ham radio contacts more interesting by including pictures?
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.
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.
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, a UFO, 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.
The Civil Air Patrol uses SSTV to send images from airplanes.
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 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.
The Russion Space Station MIR has been transmitting SSTV pictures recently.
There is a tradeoff between image quality and time. At one extreme we have low resolution (120 line) black and white images which take only 8 seconds. At the other end we have the new Pasokon TV high resolution "P" modes with 16 million colors at 640 x 480 resolution which take up to 7 minutes. Most images these days are full color 320 x 240 resolution taking almost 2 minutes to transmit.
Some countries are more restrictive, but in the U.S. SSTV can be used anywhere voice is allowed. Traditionally, certain frequencies have been used as meeting frequencies:
20 meters is generally your best bet for finding activity. 80 meters is also popular. Recently, most of the growth has been on 2 meters.
In the USA, if you are allowed to transmit voice, you are usually allowed to transmit SSTV on the same frequencies. The one exception is the Novice/Technician 10 meter segment. Other countries will have different restrictions.
Saturdays at 15:00 and 18:00 UTC on 14.230 MHz.
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 usually the nearest holiday. For example, around Holloween there is a contest for the best images with a Holloween subject matter. There are different categories for natural and computer generated images.
There is also an award for contacting at least 50 different countries with SSTV.
Amateur SSTV has been around since 1958.
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 tens of 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.
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.
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 SUPERSCAN 2001 and TSC-70 have moved in.
PC-based SSTV systems abound: Pasokon TV, SSTV Explorer, ViewPort VGA, MSCAN, and PC SSTV 5 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.
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.
Although the single op-amp receive interface is popular due to its extremely low cost, results aren't that good under noisy conditions. Those who have run other systems, such as Viewport VGA or Pasokon TV, side-by-side with the cheap interfaces consistently report that the systems with more filtering and hardware demodulation perform much better with poor signals.
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. A few years ago you had to pay $600 for a decent framegrabber. Now less than $200.
Recently, many low cost digital cameras have become available. You can transfer images from these cameras into your computer.
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.
Magazine articles in the last couple years:
Multimode, the first Mac SSTV program became available in January 1999.
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 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
For a more detailed information package, 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. #A
Chelmsford, MA 01824-1823
Either dip into your junk box or take a few dollars to your local Radio Shack store, and build the circuit in figure 1. 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 for 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 EZ SSTV, GSH-PC, JVFAX, MSCAN, ProsKan, or VESTER.