ISS SSTV Active on 145.800Mhz, Stuck PTT


The stuck PTT while running SSTV on ISS has been a known issue since the vox box was first connected to the TM-D700 in the year 2005. The ISS crew soon discovered the stuck VOX transmitter issue.

One ISS crewmember left the radio running all night sending SSTV images. The next morning the radio was excessively hot and would not respond to button commands until after the radio was “power cycled”.

The Ariss vox box does not have any RF filtering inside the device. The devices was originally designed to run on its own 9-Volt battery. At the last minute, it was modified to extract power from the TM-D700. The Ariss vox box gets its power from the D700 via a special modification to the D700 transceiver.

The unfiltered power is full of RF energy when the D700 starts transmitting.

The RF energy causes the VOX PTT circuit to get stuck in a transmitting mode until the Watch dog timer in the D700 times-out and forces the radio back to receiving mode.

Marexmg, the organization that supplied the Marex SpaceCam1 SSTV software for ISS has recommended to ARISS several times to replace the ARISS vox box with a stable USB vox box.
ARISS has repeatedly ignored any attempt to correct the problem.
Miles WF1F Marex

Leave a Reply