This terminal employs a modified Instrumentation Recorder to record multiple channels of data on 25mm (1inch) wide video tape. The reels are approx. 355 mm (14 in.) diameter andhold about 2500m (9000 ft) of tape.

The recorder typically runs at 3.4m (135 in) per second so a single pass through the tape takes about 13 min. It has a moveable headstack which allows twelve full passes giving about 3-1/2 hours recording per tape.

The rack to the right of the recorder provides 28 'video-band' channels of 2MHz each, from the intermediate frequency signal of a radio telescope, i.e. 56MHz total recording bandwidth. By recording at twice normal speed (270 ips) 112MHz bandwidth is attainable.

The terminal was designed and developed by staff at the MIT Haystack Observatory near Boston, MA, U.S.A. and is in use at about 50 sites spread around the world.

The MK3a Terminal is based upon a Metrum (formerly Honeywell) Model 96 Instrumentation Recorder.