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World of Ham Radio 1997
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1997-02-01
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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?
------
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.
------
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.
------
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.
------
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.
------
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. Some are limited to
32K or even fewer colors.
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.
------
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.
------
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.)
------
Q: Are there any nets?
A: Saturdays at 15:00 and 18:00 UTC on 14.230 MHz.
------
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.
------
Q: Is SSTV new or has it been around for a while?
A: Amateur SSTV has been around since 1958.
------
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.
------
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.
------
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
------
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.
------
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.
------
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.
Anyone who has ever tried Pasokon TV will tell you it is
the best.
------
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
------
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.
------
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
------
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
------
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.
------