First delivered by ITT in 1984, a 1996 study by analysts from Battelle Memorial Institute determined problems with repair of the ALQ-172 resulted in the highest cost per flying hour (CPFH) of any system on the B-52.[5][6] The United States Air Force instituted Engineering Change Proposal (ECP) 93 modifying the system's memory and processing capability. The ECP 93 modifications upgraded ALQ-172(V)1 line-replaceable units (LRUs) 1, 3, 4, and 10 and replaced LRU 2 resulting in the enhanced ALQ-172(V)3.
Also in FY96, Air Staff directed the enhanced ALQ-172(V)3 be installed on AC-130H gunships replacing the earlier (V)1 version of the ALQ-172, and non-supportable AN/ALQ-131 jamming pods.[5] Also on special operations forces (SOF) AC-130U, MC-130H and MC-130E aircraft, an additional ALQ-172 subsystem was installed, bringing the number to 2 sub-systems; one forward and one aft, with a single common display and control unit. Other engineering differences on these aircraft involved adding low-band countermeasures transmitters, antennae and antenna control units.[5]
By fiscal year 1997 (FY97), the same group reported a second system was needed on the aircraft for full threat protection.[5]
Further upgrades have incorporated geolocation capabilities, advanced countermeasures and new technologies.[7][8] The upgrades are part of the 2021 maintainability and reliability system (MARS) upgrade;[3] a 10-year, $947 million project enhancing the performance of the B-52's electronic countermeasures systems.[8][6] Nine line-replaceable units (LRUs) have been upgraded, with five of those tested by mid-2024[update].[8] As part of the MARS contract, LRUs 1, 3, 4, and 10 have been upgraded with LRU-2 being replaced with a new high-voltage power supply. With continuing support and upgrades, the ALQ-172 is expected to be in service well into the 2040s.[7]
Technical description
Features
Integrated with aircraft controls and displays, the system provides countermeasures capabilities for multiple sophisticated pulse, continuous wave, doppler and monopulse threats simultaneously.[1][7] Using digital frequency discrimination (DFD) technology, the system is capable of determining pulse width, angle of arrival (AOA), and pulse-repetition frequency (PRF) of threat signals, deinterleaving and processing them.[5] Countermeasure techniques available to the ALQ-172(V)3 include spot noise, barrage noise, swept noise, range/angle deception, cross-eye, and false target generation.
Based on the MARS upgrades, the below list contains information regarding components of the AN/ALQ-171(V)3 version of the jammer.
LRU-1: Countermeasures Receiver / Receiver-Processor[7][9] – Detects and digitizes threat radar emissions; pulse characterization (pulse width, PRF), AOA estimation, de-interleaving and threat signal processing. Part number: R-2247/ALQ-172
LRU-2: High-Voltage Power Supply (HVPS) / Power & Cooling Distribution[10] – Supplies high-voltage power required by transmitter/modulator stages; provides power conditioning and supports cooling/air distribution interfaces. Noted in field support/repair solicitations. Part number: A301402-1
LRU-3: Modulator / Antenna Control / Timing Processor[7][10] – Handles waveform modulation/timing for transmitters and/or controls antenna switching and low-level RF routing; subject of wiring/TCTO changes in field engineering records. Part number: A301405-1
LRU-4: Countermeasures Transmitter / Power Amplifier[7][8] – High-power ECM transmit functions: amplification of PR, PD and CW ECM waveforms, deception waveform generation and often part of antenna T/R group. Part number: A301408-1
LRU-5: Chassis / Equipment Mounting / Interface[11] – Structural/electrical equipment assembly containing non-RF electronics, mounting, aircraft interface and I/O connections; naming varies across variants. Part number: A301410-1
LRU-6: Antenna Amplifier / Receiver Converter[7][3] – Quadrant amplifier / blade amp assemblies for receive/transmit conversion; mid/high-band amplifier converters used in the antenna group. Part number: A301414-1
LRU-7: Auxiliary Receiver / Processor / Packaging Module[10][11] – Auxiliary receiver/processor or module appearing paired with other LRUs in packaging/field support documentation; role varies by installation. Part number: A301416-1
LRU-8: Control / Display / Human-Machine Interface (HMI) Unit[7] – Crew interface and control electronics (display, control panel, I/O); sometimes split into separate LRUs depending on installation. Part number: A301420-1
LRU-9: Support / Conditioning / RF Filter / RF Switch Assembly[12] – RF switching, filtering, bias supplies and small support modules that route signals between receivers, processors, and transmitters; listed in upgrade/field-support summaries. Part number: A301425-1
LRU-10: Processing / Upgrade Module (subject of MARS upgrades)[10][12] – Identified in SRD/upgrade documents as a significant module targeted for upgrade alongside LRUs 1,3,4; likely contains processing, digital logic or waveform generation elements. Part number: A301430-1
Variants
AN/ALQ-172(V)
AN/ALQ-172(V)1 – on MC-130H Spectre and AC-130U Spooky aircraft[1][5]
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