ao-16 recovered for voice operation
amsat vice president of operations drew glasbrenner, ko4ma, said this week the ao-16 satellite was successfully reconfigured as a voice repeater. in orbit since 1990, ao-16 had a serious on-board computer failure. the satellite was partially recovered approximately 6 months ago with its beacon and boot loader operational. however, ao-16 could not support any user traffic because of this failure.
a team which included bruce rahn, wb9anq and jim white, wd0e, advising mark hammond, n8mh as the primary groundstation performed a series of memory tests points toward a hardware failure which prevents restarting the spacecraft's original mission software successfully. mark put in many early hours during the multiple reloads and test sessions, with bruce, jim, and others advising.
after the conclusion that the spacecraft computer system was damaged and as discussions about decommissioning were taking place, jim recalled a series of low level commands included in the spacecraft design by tom clark, k3io during construction. one of these commands allows an uplink receiver to be directly tied to a downlink transmitter. the twist is that the uplink is regular fm but the downlink via the bpsk transmitter is dsb (double sideband).
mark placed the satellite in this mode and some testing was undertaken. the satellite hears very well, and the reduced bandwidth by using either usb or lsb on the groundstation receiver allows for a very robust downlink. tuning the downlink is just like on a linear transponder, meaning it is tight and with fast doppler. uplink tuning is not required, just as with the fm mode v/u satellites.
with testing complete the operations team announced the satellite is now open to general use on voice for a test period. the uplink is 145.920 mhz fm, and the downlink is 437.026 mhz ssb +/- doppler shift. please restrict your uplink power to a reasonable level, and do not transmit without being able to hear the downlink. all the general single-channel guidelines apply.
ao-16's receiver has a 15 khz wide crystal filter with sharp skirts. so if your nbfm transmitter is set with a ±5 khz deviation, you may well find your signal hitting the filter "walls". you may get better performance if you crank the deviation back a bit. the 70cm transmitter antenna configuration is left hand circular polarity (lhcp). the 2m receiving antenna is a 1/4 wave whip.
operators report the fading is quite dramatic, which means the bird is spinning and tumbling. we could never hear this before on ao-16 when it was transmitting its normal psk signal, since we didn't hear the effect of fading on the uplink in this mode. with voice operation the fading effect is quite apparent.
reports of successful contacts via ao-16 have been received from around the world. the downlink has even been copied indoors with a temporary antenna. enjoy ao-16's new life! thank you to all involved for your hard work.