THE HARTLOBE AIRBORNE DUAL ANTENNA SYSTEM FOR IFF. PART I. MARK X (SIF) SYSTEM.

Abstract : The experimental model (Plan 1) of the Hartlobe airborne dual antenna system for IFF which was successfully flight tested by NATC had an inherent problem caused by gain-time-control (GTC) action in the interrogator receiver. An improved model, designated Plan 2, which overcomes the GTC problem, has been developed. The GTC problem resulted from the fact that the bottom transponder was allowed to reply to all signals above its sensitivity threshold, while the top transponder was triggered only when the bottom unit did not reply. At certain aircraft aspects, the reply failed to register because of the GTC threshold. This problem was overcome by circuitry which compares the signal levels in the two receivers and directs the reply via the antenna which produced the strongest received signal. It is proposed to implement the Hartlobe system by utilizing components of the AN/APX-72 transponder or other lightweight transponder capable of easy separation into rf and video portions. (Author)