How to be successful with the ISS Slow Scan
TV (SSTV) Imaging system
By G. Miles Mann, WF1F MAREXMG for the ARISS-International
Team
There are currently two projects on board the International Space Station
that will support Slow Scan TV (SSTV). These projects are called SuitSat
and SpaceCam. The SuitSat project may be activated in December 2005 and
SpaceCam in 2006 (all dates are subject to change without notice).
The goal of this series of memos is to get the world ready to start decoding
SSTV images from Space. If you want to get Ready for SuitSat and SpaceCam
Slow Scan TV, then now is the time to start getting ready.
How to Slow Scan TV from Space, Part 1.
Slow Scan TV on the International Space Station:
The ISS Slow Scan TV system will support two-way SSTV
image transmission. SSTV is a form of sending still images via an Analog
format by radio. Amateur Radio operators have been using SSTV since the
1950’s. Today there are many software applications available that
will allow you to connect your home computer to a radio and allow you
to decode images from space.
The Basics:
The Slow Scan TV system on the International Space Station that I will
be focusing on is called SpaceCam1. The SuitSat Project may be activated
first, however the functionally is very similar. The SpaceCam1 project
is a PC based application that will be running on board the International
Space Station. The system will be connected to an Amateur Radio transceiver
called the Kenwood D700. This radio will
transmit on the Amateur radio 2-meter satellite band from the ISS (The
exact uplink and down link frequencies will be posted later). The transmission
mode will be FM (aprox 4k deviation) and will be sending images in the
Slow Scan TV format called Robot-36.
When SpaceCam becomes operational, it will be transmitting over 400 images
per day from the International Space Station. The crew will load a directory
full of still images taken earlier and then tell SpaceCam to run “Slide
Show”. SpaceCam will then keep sending the images from the directory
over and over again. This will allow people on earth several chances to
decode all of the images from the directory on board the International
Space Station.
The SpaceCam slide show will be configured for a specific delay between
images. Lets assume the delay is set for 3 minutes. The Space Station
will pass within radio range of your house several times a day for up
to 10 minutes per pass. During a typical 10-minute window you will have
the opportunity to receive 2-3 images per pass.
SpaceCam & Kenwood D700 System:
The Kenwood transceiver that has a built in Packet modem. This system
is located in the Service Module. The Kenwood model D700 supports two
Amateur radio bands: 2-meter FM (144 – 146 MHz) and the 70-centimeter
FM (435 - 438 MHz). The built-in modem or TNC supports 1200 and 9600 baud
data rates.
The D700 is currently connected to one of the 4 Amateur Radio antennas
mounted outside of the Service Module. The typical power output of this
system is 5, 10 or 25 watts. The Kenwood D700 system was activated in
December 2003. The D700 will also be the primary radio for the SpaceCam
SSTV project. The ISS crew will connect the D700 to a laptop computer
via a custom designed adapter module made by ARISS. The VOX-Box will match
the audio signals from the laptop computer to the D700 radio. The VOX-box
will also signal the radio when it is time to transmit.
What do I need at home?
To work ISS from your home, you should have at least the following Amateur
Radio equipment:
A 2-meter FM radio with an output rating of 25 to 50 watts.
An Omni-directional antenna or small beam (the higher
the gain the better). A short run of good quality coax (RG-213, 100 feet
or less). A PC running one of the common Slow Scan TV decoding applications.
(In this memo I will not go into the details of any one specific SSTV
applications at this time.)
And that is it for radio equipment. I use an inexpensive Laptop computer
with a 233 MHz CPU and Windows 2000. The software I use is either CPIX
by Silicon Pixels or an engineering version of SpaceCam1 (Sorry, SpaceCam1
is not for sale).
Slow Scan TV Decoding Software:
Here are just two of the many Share-Ware SSTV
applications on the market. There may be many more.
W95SSTV by Silicon Pixels
http://www.barberdsp.com/w95sstv/w95dload.htm
MMSSTV
http://mmhamsoft.ham-radio.ch/
There are also many High quality pay software applications that offer
many more features, such as multiple windows that allow you to simultaneously
receive an image while preparing your next image that you want to transmit.
CPIX
http://www.barberdsp.com/
Timing:
You will need access to a computer or web to tell you when ISS is in range
of your station. The timing of your contact is the most important part
of a successful contact with ISS. There are many tracking programs out
in the market place today. The ARISS team does not endorse any specific
tracking program. Some programs are share-ware (STSPLUS); others cost
a few bucks. I recommend using the DOS InstantTrack, program by AMSAT.
This program is very easy to use and works very well with older style
computers such as 80286 style PC's. The cost of most tracking software
applications is approximately $50-100.
Doppler Shift:
The ISS Space Station is traveling around the Earth at over 17,500-mph
(28,000 Kph). This great speed will make radio signals appear to shift
in frequency. This phenomenon is called Doppler Shift. Many of us have
radios that are channel locked. This means you cannot make any fine tuning
adjustments to your receiver or transmitter's frequency. Most Mobile and
HT radios cannot make any frequency changes less than 5 kHz channel steps
(lets hope that radio manufacturers will add 1 or 2 kHz channels steps
in the future). This Doppler shift will cause the ISS transmit frequency
(145.800) to look as if it is 3.5 kHz higher in
frequency when ISS is approaching your location. Fortunately we will be
using the FM mode, and this mode does help compensate for part of the
Doppler frequency drift automatically. If you are fortunate enough to
have a radio with the ability to make smaller channels steps then you
should take advantage of this feature. You will need to review the owner's
manual for your radio to learn how to program "Odd-Splits" channel
combinations and program the
following consecutive frequencies into your radios'
memories.
For 5 kHz channel step radios do not try to adjust for Doppler. The exact
frequency for Slow Scan TV has not been announced at this time.
( Region 2--North & South America, Region 3Asia,
Australia)
Channel 1 145.800.0 RX 144.490.0 TX Voice
Channel 2 145.800.0 RX 145.990.0 TX Packet (Worldwide)
Channel 3 145.800.0 RX 145.200.0 TX Voice (Region
1Europe, Africa)
For VOICE (Region 2North & South America, Region
3Asia, Australia)
2.5 kHz channel step radios
Channel 1 145.802.5 RX 144.487.5 TX
Channel 2 145.800.0 RX 144.490.0 TX
Channel 3 145.797.5 RX 144.492.5 TX
For Packet 2.5 kHz channel step radios (Worldwide)
Channel 4 145.802.5 RX 145.987.5 TX
Channel 5 145.800.0 RX 145.990.0 TX
Channel 6 145.797.5 RX 145.992.5 TX
For VOICE (Region 1Europe, Africa) 2.5 kHz channel
step radios
Channel 7 145.802.5 RX 145.197.5 TX
Channel 8 145.800.0 RX 145.200.0 TX
Channel 9 145.797.5 RX 145.202.5 TX
Let's assume ISS is approaching your location (QTH) and the Slow Scan
TV system is active. Use channel #4 at the beginning of the pass, then
when ISS is over head, use channel #5 and when ISS passes your QTH use
channel #6. For best results, use an updated tracking program, which displays
the current Doppler shift. This will assist you in determining when it
is best to change channels.
As you may have noticed, it is not recommended for you
to adjust your uplink frequency on 5 kHz radios. You may have better results
if you leave your receiver on 145.800 and your transmitter on 145.990.
The Doppler shift is only at the +3.5 kHz setting for a few seconds, then
it will slowly begin to approach zero. After 5 minutes or less, the Doppler
shift will be 0 for a few seconds, and then it will begin to swing
towards -3.5 kHz.
What is Slow Scan TV:
On this web page you will find many links to help you
learn more about Slow Scan TV
http://www.marexmg.org/fileshtml/sstvlinkpage.html
Practice Practice Practice:
If you want to be successful in sending and receiving Slow Scan TV from
ISS you must be fully proficient in using Slow Scan TV on Earth first,
before you make any attempt to use the Slow Scan TV on ISS.
If you can not find any friend locally to test with on 2-meter, you can
always try 20-meter (14.230 USB, assuming you have license privileges
and equipment). During most of day and night you can easily hear people
sending SSTV images on the 20-meter band. On HF the most common SSTV analog
mode is called Scotty-1. Most SSTV applications support several of the
common SSTV modes.
You can also experiment with SSTV by plugging two
computers together, PC to PC via the sound card audio
cables.
Receiving Images from Space:
The SuitSat project will only be sending an image. The SpaceCam project
later on, will allow both Uploading and down loading of images from ISS.
The Schedules for SpaceCam will be posted early next year. For now you
will just need to concentrate on receiving SSTV images from space.
Picking A Pass:
Use your computer program to select a good pass with high elevation angles.
When ISS first appears on the horizon, the satellite will be 1500 miles
(2400 km) away. When ISS is directly over your house, it is only 240 miles
(384 km) away.
Using your tracking program, pick a pass with a maximum elevation of over
40 degrees. These are typically the best passes because ISS will be closer
to your QTH. For low elevation angles, your radio signal will have to
travel along the ground, where it will be affected by trees, buildings
and hills. When ISS is high above the trees, you will have a clear
line-of-site shot to the ISS antenna. A 1000-mile contact on 2-meters
is easy, that is if there is nothing between you and the other station.
A good pass is only 10 minutes long.
Receiving SuitSat:
The SuitSat Transmitter is preprogrammed to send a series of Voice messages,
Telemetry and a single SSTV image, every 8:46. Then the whole process
then repeats from the beginning. This means that each orbit over your
house you will have one or two chances to receive and decode the image
from SuitSat. You may also want to have your tape recording device handy
to record the rest of the messages. The exact location of the image is
approximately 6:42 seconds from the start of the first message.
Don’t wait to try SSTV:
As more information becomes available on the activation dates
of the project, the information will be posted. It is possible that SuitSat
may be activated in December 2005.
If this it true, they you only have a few weeks to get your home station
ready to receive SSTV images from Space.
So, don’t wait until the last minute to get your home station SSTV
ready.
73 Miles WF1F MAREX-MG
Until we meet again
DOSVIDANIYA Miles WF1F
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