Lockheed SR-71 Blackbird by Paul Crickmore

Author:Paul Crickmore
Language: eng
Format: epub, pdf
ISBN: 9781472804945
Publisher: Osprey Publishing
Published: 2015-09-21T16:00:00+00:00

Electronic Counter Measures (ECM)

The SR-71 did not carry any form of defensive weaponry save that which was generated electronically. ECM was and remains a highly sensitive area, where fast-moving technological advances meant that the SR-71’s Defensive Electronic systems (DEF) required continual updating throughout its operational life. The controls required to operate all the DEF systems were located on a single panel on the RSO’s left console, an arbitrary alpha-numeric system was used to identify equipment fit, and at the time of its retirement, the aircraft was equipped with systems A2, C2, H and M.

A2 was an ECM jammer system designed to protect the aircraft from airborne threats operating in the X-band frequency band. It consisted of two sets of receive and transmit antennas, and a gaseous nitrogen system to pressurize the transmit waveguides. The receive antennas were located in “blisters” on the left and right sides of the nose chine and identified the threat as coming from below the aircraft in either the left or right forward quadrants. A2’s transmit antennas protruded slightly from the lower surfaces of the chines, opposite the pilot’s cockpit. The DEF A2 system was interfaced with the MRS, radar and EMR system and when mission requirements dictated, the received signals could be recorded for later analysis on the AR1700 recorder.

C2 worked in conjunction with DEF H to protect the SR-71 from the SAM threat. It consisted of a receiver, band antenna, band-pass filter, power relay, and electrical and coaxial cables. On receipt of a signal received from DEF C2 the DEF H system was triggered into operation.

Carried in compartment bay K and weighing in at 900lb, DEF H was an extremely powerful piece of kit that provided threat warning and, when required, barrage noise jamming for protection against the SAM threat. It included a transceiver, two transmitting systems, an interface unit (IU), a data processor and an evaporative cooler. Radar signals associated with the various SAM threats (essentially the SA-2 or SA-5) were captured by two sets of receivers. Those signals, received by a forward centerline antenna, were sent to the transceiver. Signals received by an aft centerline antenna were routed to the DEF H system through a band pass filter and preamplifier. The IU controlled the jamming pulses generated by the transmitting systems. The transmitting systems were designated as low band or high band and each band could be driven by commands from the DEF control panel. Upon receipt of signals from DEF C2, DEF H transmitted on frequencies predetermined by the LO and/or HI band selections on the RSO’s DEF console. Signals received by DEF H could if required be recorded on the AR1700 recorder for later analysis.

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