SB SPACE @ ARL $ARLS012<BR>ARLS012 AO-40 Transponders Back on the Air!<P>ZCZC AS12 <BR>QST de W1AW <BR>Space Bulletin 012 ARLS012<BR>>From ARRL Headquarters <BR>Newington, CT July 20, 2001<BR>To all radio amateurs<P>SB SPACE ARL ARLS012<BR>ARLS012 AO-40 Transponders Back on the Air!<P>AO-40's transponders are back on the air, following an orbital shift<BR>that put the Amateur Radio satellite into an orbit that AMSAT says<BR>should be good for many years to come. Transponders have 435 MHz and<BR>1.2 GHz uplinks and a downlink in the 2.4 GHz ''S band.''<P>The transponders have been off since late May, when preparations<BR>began to shift AO-40's orbit at perigee. That operation was<BR>completed earlier this month, and ground controllers have been<BR>readjusting the spacecraft's attitude since then.<P>Ground controller Stacey Mills, W4SM, said the transponders would<BR>operate from orbital positions MA 10 through MA 99. Uplink<BR>frequencies (without taking Doppler into account) are<BR>435.495-435.780 MHz and 1269.211-1269.496 MHz, and the downlink<BR>passband is 2401.210-2401.495 MHz. The transponders are inverting,<BR>so a downward change in uplink frequency results in an upward<BR>frequency shift in the downlink.<P>Mills emphasized that earthbound ops should not use any more uplink<BR>power than necessary. He also noted that the transponders could be<BR>switched off to accommodate additional testing.<P>AMSAT Awards Manager Bruce Paige, KK5DO, in Houston, was among the<BR>first stations to get on AO-40 after the transponders were<BR>reactivated. ''It sounds awesome,'' Paige said. ''I am transmitting<BR>with 25 watts up, and it sounds great!'' In addition to some domestic<BR>contacts, he and his daughter, Mahana, W5BTS, worked EA8/DJ9PC in<BR>the Canary Islands.<P>Although AO-40's attitude still is not optimal at this point, ground<BR>controllers had to suspend operations to adjust it after an onboard<BR>sensor lost its view of the sun. Without data from the sun sensor,<BR>ground controllers cannot be certain of the satellite's attitude.<P>Mills said now that the ground team has ''a very good fix'' on the<BR>spacecraft, they'll do nothing to change its attitude for several<BR>weeks, while the solar angle decreases. Once the sensor regains its<BR>view of the sun, efforts to adjust the spacecraft's attitude will<BR>resume, so that AO-40's antennas are pointing toward Earth.<P>Mills said ground controllers will use the interim period to see if<BR>they can re-calculate the so-called ''mystery effect'' that had been<BR>impacting AO-40 at perigee under its former orbit.<BR>NNNN<BR>/EX