AMSAT-NA says thethe SO-50 satellite–also known as SaudiSat-1C–now is available to all, and users can switch on the Mode J transponder via a CTCSS tone.
Previously, only one of the three control operators could turn on the spacecraft for amateur communication. Here’s the procedure: Transmit on 145.850 MHz (taking Doppler effect into account) using a CTCSS tone of 74.4 Hz to arm the onboard 10-minute timer. Then, transmit FM voice on 145.850 MHz using a CTCSS tone of 67.0 Hz to actuate the repeater within the 10-minute window (SO-50 takes a half second or so to start transmitting once a signal is received, so users should pause briefly before talking). SO-50’s downlink frequency is 436.800 MHz. Sending the 74.4 Hz CTCSS tone again within the 10-minute window resets the timer.
Launched in December 2002, SO-50 sports a quarter-wave vertical receiving antenna mounted at the top corner of the spacecraft. The transmitter runs 250 mW into a quarter-wave antenna mounted on the bottom corner of the spacecraft and canted 45 degrees inward.
http://www.amsat.org/amsat/sats/n7hpr/so50.html