March 17, 2006

How to use SSTV on ISS Slow Scan TV (SSTV) Imaging system

By G. Miles Mann, WF1F MAREXMG  for the ARISS-International Team

Slow Scan TV SpaceCam1 on ISS:

All required SSTV software, data cables, antennas and radios are currently on ISS.

We are just waiting the assignment of a laptop and a time-line.

No official start date at this time.

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 SpaceCam1 project is a windows based PC 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 (Standard voice grade FM, approximately 4k deviation) and will be sending images in the Slow Scan TV format called Robot-36.  When SpaceCam becomes operation, 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 2 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.

Note:  Total time between pictures for a 2 minute delay will be approximately 163 seconds (120 seconds of delay plus 43 seconds of image transmission time)

SpaceCam & Kenwood D700 System:

The Kenwood D700 transceiver will support normal Voice modes, SSTV modes and has a built in Packet modem. This system is located in the Service Module.  The Kenwood 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 (Antenna WA1, Earth facing).  The typical power output of this system is 5, or 25 watts, this default is usually 10 watts.  The 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  or and 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

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 your 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. www.amsat.org  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.

Current ISS channel list with Doppler corrections listed:

If you are only planning on listening to the ISS Downlink, then set your receive to monitor 145.800 MHz.  If you have a valid amateur radio license, then program you transceiver to use the listed transmit frequency for Mode and country region.

For 5 kHz channel step radios do not try to adjust for Doppler. 

 ( Region 2--North & South America, Region 3Asia, Australia )

Channel 1 145.800.0 Receive, 144.490.0 Transmit Voice

Channel 2 145.800.0 Receive, 145.990.0 Transmit Packet (Worldwide)

Channel 3 145.800.0 Receive, 145.200.0 Transmit Voice (Region 1Europe, Africa )

If your radio supports fine channel adjustments, then try these settings.

For VOICE (Region 2, North & South America, Region 3Asia, Australia )

2.5 kHz channel step radios

Channel 1 145.802.5 Receive, 144.487.5 Transmit

Channel 2 145.800.0 Receive, 144.490.0 Transmit

Channel 3 145.797.5 Receive, 144.492.5 Transmit

For Packet 2.5 kHz channel step radios (Worldwide)

Channel 4 145.802.5 Receive, 145.987.5 Transmit

Channel 5 145.800.0 Receive, 145.990.0 Transmit

Channel 6 145.797.5 Receive, 145.992.5 Transmit

For VOICE (Region 1Europe, Africa) 2.5 kHz channel step radios

Channel 7 145.802.5 Receive, 145.197.5 Transmit

Channel 8 145.800.0 Receive, 145.200.0 Transmit

Channel 9 145.797.5 Receive, 145.202.5 Transmit

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.  Note: the official SSTV channel has not been selection.  I am using the packet frequency pair for this series of memos.

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 and 14.233 USB, assuming you have license privileges and equipment).  Short-Wave-Listeners are welcome to try to decode the SSTV activity 14.230 & 14.233 with your USB receiver.  During most of the 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, including Robot-36 and Scotty-1, just to name a few. 

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 SpaceCam project will allow both Uploading and down loading of images from ISS.  The Schedules for SpaceCam will be posted later this 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 house (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 SpaceCam Images:

The SpaceCam Transmitter

The SpaceCam system will try to give you some help to get ready to receive an image by sending out a special DTMF tone and a CW ID, followed by the SSTV image.  The device that tells the radio when to transmit is called a VOX controller.  It’s a device that when it hears sound from the PC, it will set the radio into a Transmitting mode.  The VOX will keep the radio transmit until 3 seconds after the sound data from the PC stops.  There is also a safety circuit in the transmitter that will shut down if the transmitter is on for too long.

First SpaceCam will send a DTMF tone (asterisk) for 2-3 seconds to the VOX controller transmitter.  The DTMF tone will start the D700 transmitter on ISS. 

Next SpaceCam will send the CW ID of the station in Morse code RS0ISS.

A second or two after the CW ID stops, SpaceCam will begin transmitting the SSTV image in Robot-36 format.  The SSTV image transmission will last 36 seconds.

When you hear that CW coming down from ISS you will have a few seconds to fine tune you station and make sure your computer is ready to receive the new image from ISS.  If the signal is strong, then your SSTV program should automatically Start decoding the image in real-time.  If the signal is very weak, you may miss the SSTV Start-Pulse.  If that happens, just hit the Manual-Receive button on your SSTV program.