Artifact: Amplifier, Unified S-Band, Apollo Command Module, Block II

Apollo Command Module S-Band Power Amplifier (Manufactured by Collins Radio Corp.) This traveling wave- tube (TWT) power amplifier is housed in a sealed and pressurized case 5.75 by 5.56 by 22.26 inches and weighs 32 pounds. It has two independent amplifiers, either of which can amplify outputs of either the phase- modulated or frequency modulated unified S-band transmitters within the S-Band Transponder Assembly (see previous artifact entry for discussion of the S-Band Transponder). It operates on 3-phase, 1 15/200 volt, 400 Hertz power and supported two power outputs of 2.8 and 11.2 watts. The amplifier increased the low-power output of the unified S-band equipment to high power.

The S-band power amplifier equipment was used to amplify the radio frequency output from the S-band transmitters when additional signal strength was required for adequate reception by the ground. The amplifier equipment consists of a triplexer, 2 traveling-wave tubes for amplification, power supplies, and the necessary switching relays and control circuitry housed within a single electronics package located in the Apollo Command Module's lower equipment bay. .

All received and transmitted S-band signals passed through the triplexer. For the receive leg (Mission Control or the Lunar Module to the Command Module), the S-band carrier uplinked to the spacecraft entered the triplexer from either the s-band Omni-Directional or High Gain antenna equipment. The triplexer then relayed the signal straight through to the S-band receiver. The downlinked signal (CSM to the LM or Mission Control/JSC) from the S-band transponder entered the S-band power amplifier where it was either bypassed directly to the triplexer and out to the S-band antenna equipment, or amplified first and then fed to the triplexer. There were two power amplifier modes of operation: low power and high power. The high-power mode is automatically chosen for the power amplifier connected to the FM transmitter.