# AN/ALR-20

AN/ALR-20(A) is an airborne wideband tuned radio frequency receiver providing a panoramic display of Radio Frequency (RF) spectrum on US Air Force B-52 Stratofortress aircraft. As a stand-alone system, it is used by the Electronics Warfare Officer (EWO) to evaluate and determine various classifications of threats to the aircraft, identifying various signals including search, acquisition, and tracking radars as well as communications. Because it allows a broad view of the RF spectrum, its situational awareness also provides for analysis of the efficacy of jamming techniques employed by the EWO using other systems. First manufactured in the late 1960s, the system is a passive Electronic Support Measures (ESM) tuned radio frequency receiver. It is the primary tool used by the EWO to evaluate threats.

## History

First developed in the early 1960s, the ALR-20 began appearing on B-52D bombers (before 1967) and B-52Gs in 1967-1969. In accordance with the Joint Electronics Type Designation System (JETDS), the "AN/ALR-20" designation represents the 20th design of an Army-Navy electronic device for passive countermeasures signal receiver. The JETDS system also now is used to name Air Force systems.
The ALR-20 did not undergo any significant upgrades or design changes until the 1980s when solid-state components were added to the system's tuners upgrading older tube-based technology. At the beginning of the 1990s, the outdated panoramic display (using old cathode ray tube technology) needed replacement due to the existing display becoming unsupportable. Until the late 1990s, the ALR-20's panoramic receiver display utilized Cathode-Ray Tube (CRT) technology. This replacement was delivered in the late 1990s. At that time, tuners and the power supply were determined to also need replacement for the same reasons. Today, deployed on B-52H bombers, the system still provides the EWO a display of six different RF bands, allowing for detection and identification of threat signals.
Into the early 2000s, it was determined the system was "becoming unsupportable due to vanishing vendors and obsolete technology". Under the B-52 Situational Awareness Defensive Improvement (SADI) program, the ALR-20 is expected to be replaced with a defensive system upgrade. The upgrade is expected to create up to thirty-fold improvements in reliability. Efforts to replace the ALR-20 continued into the mid-2000s, while some work was done to continue maintaining line replaceable units (LRUs). In 1999, ninety-one LRU-1s, fifty-four LRU-3s, thirty-six LRU-8s, eighty-three LRU-9s were repaired at a total cost of over $315,000. According to the Air Force's Fiscal Year (FY) 2004/2005 budget estimates, SADI would cost just over $70.9 million.
Electronic Warfare Officers undergo extensive training concerning the ALR-20 panoramic system.

## Technical description
### Features

The ALR-20's panoramic display is the EWO's primary source for analysis of potential threats through a very wide part of the electromagnetic spectrum. The early cathode-ray tube for the display (seen in the image to the right) had an orange tint displaying six different horizontal lines that represented a part of the spectrum. The signals displayed on those lines may be quickly analyzed allowing the EWO to bring the proper countermeasures for multiple different threats at once.

### Components

* Receiving Set Controller - LRU-1
* Panoramic Display
* Power Supply - LRU-3
* Radio Frequency Tuner - LRU-8
* Radio Frequency Tuner - LRU-9

## Variants

* AN/ALR-20
* AN/ALR-20A