The AO-40 team has announced that experimental transponder operation will start on Saturday, May 5, at approximately 0800z. The announcement comes in the wake of successful initial transponder tests last weekend. ''We expect good conditions on Saturday morning over North and South America and Europe,'' said AMSAT-DL President Peter Guelzow, DB2OS, an AO-40 team leader. Guelzow said the 435 MHz and 1.2 GHz uplinks will be connected to the 2.4 GHz transmitter passband. It's estimated that AO-40 will be available on May 5 in the Western Hemisphere from 0800 until approximately 1400z. Stations should use only SSB and CW. Guelzow said it's expected the transponders will remain available over a period of approximately 10 days. The uplink frequencies are 435.550-435.800 MHz and 1269.250-1269.500 MHz. The downlink passband is 2401.225-2401.475 MHz. The transponders are inverting, so a downward change in uplink frequency will result in an upward frequency shift in the downlink. Users are asked to avoid the ''middle'' 2.4 GHz telemetry beacon and give it a clearance of 5 kHz on either side. Guelzow said the transponder might be shut down if the beacon cannot be copied because of interference. He emphasized that the operation is experimental, the schedule subject to change, and the transponders could be shut down at any time without warning. AO-40 ground controllers also plan to test the problematic VHF and UHF transmitters again.