[amsat-bb] ISS Slow Scan hardware/software

MM ka1rrw at yahoo.com
Wed Jan 27 12:03:55 PST 2010

Slow Scan TV Stuff:
There are three different SSTV projects on ISS.
#1 Kenwood  VCH1 Communicator (flight approved)
#2 PC based software called SpaceCam1 from Marexmg.org (flight approved)
#3 PC based software called MMSSTV (not flight approved)
Only the Kenwood VCH1 and Marex SpaceCam1 projects were approved for flight.  The MMSSTV software was an untested back door project.
The VCH1 Communicator is a microphone with a camera, that plugs into the Kenwood TM-D700 transceiver.  The camera requires four (4) AA batteries.  The camera did not pass an external power flight safety test and cannot be plugged into an external 6 volt power source.  Without batteries the camera will not run.
The VCH1 will consume a full set of 4-batteries in 4-8 hours.  Batteries weigh 25 grams each or approximately 3.5 ounces for a full set.  It costs approximately $10k per pound to send cargo to the ISS via the shuttle.  
One set of batteries for the VCH1 cost approximately $2,800.
The VCH1 is only used, when there is a set of batteries that have reached the end of useful life from other more critical projects.  The mostly dead batteries are then used on the VCH1 until they are complexly dead.
The PC software SSTV projects run off of station power and do not need batteries.  The SpaceCam1 SSTV projects supports most of the common SSTV protocols.  It also has some great features requested by the Mir crew, such as a Slide show mode that will stream a disk directory of images continually or live USB camera images.
The SpaceCam1 and all other laptop to Radio applications cannot be used unless they are constantly monitored.  This is because the Vox box (“ISS-HAM SSTV/VOX”, part number SXISS00500)  that connects between the laptop and the Kenwood TM-D700, locks the radio in Transmitting mode.
The most logical reason for the lockup is RF feedback jamming the Op-amp that controls the transmit signal to the radio.  During 2+ years of ground testing the Vox box was tested with an external 9-Volt battery to power the Vox box.   A few months before flight to ISS, the Vox box was modified to get its power from a 13.5 volt source inside the TM-D700 transceiver.  The existing 6-Pin Din on the D700 was removed and an 8-Pin Din connector installed.  The 2 extra pins were used to tap off a 13.5 volt source from some unknown location inside the D700.
According to the Vox box schematic, there does not appear to be any RF decoupling on the power or audio leads.  The voltage sources also changed from 9 volts to 13.5 volts DC.  The Vox box, also does not contain any type of mechanical bias to adjust the TX / RX control levels.
Both boxes sent to ISS failed the same way, the first time you send and image from the laptop to the D700, the transmitter stick on for 3 minutes (the internal watch dog timer will stop the TX after 3 minutes).  The process repeats until you disconnect the Vox box from the D700.
If you would like to see a continuous steam of SSTV images from ISS, the I suggest you contact the educational departments of your ISS space agencies and request the USB Vox replacement project be sent to ISS.  The exiting ARISS hardware team is content with the way the “ISS-HAM SSTV/VOX” is currently running.

USB Vox replacement project

Kenwood VCH1

73 wf1f Miles


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