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Radio Transmitting Equipment AN/ART-4(XA-3) & AN/ART-4(XA-4) constitutes the transmitting portion of the Firing Error Indicator and are to be used and operated in conjunction with Firing Error Indicator Radio Receiving Equipment AN/GRR-1 (XA-2).

These transmitters emit frequency modulated signals produced by shockwaves, from passing projectiles, impinging on two condenser microphones MI-101. Owing to the characteristic variation of the intensity of shockwave pressure with distance from the trajectory, the magnitudes of the excitation of the two microphones, if properly identified, may be used to yield signals indicative of both miss distance and miss direction of the projectile. This identification is provided by using independent transmitters with each microphone, one operating at 55.5 megacycles, the other at 56.75 megacycles. This acoustic target transmitter will therefore produce two carrier waves each of which is frequency

modulated by the capacity changes of the respective condenser microphone. Radio Receiving Equipment AN/GRR-1 (XA-2) will then translate the frequency changes into indications useful to the gunner.

AN ART-4.png


Reference Files

Adobe_PDF_icon.png TM 11-893[1]
Operating and Maintenance Instructions
Radio Transmitting Equipment
AN/ART-4 (XA-3)
AN/ART-4 (XA-4)
March 1948


  1. TM 11-893,
    "US Army Technical Manual Collection,"
    from the CECOM Historical Office archive, Aberdeen Proving Ground, MD.
    CECOM Historical Office