Abstract: A transmitter generates three signals for sequential transmission. These signals are an unmodulated r.f. carrier, an r.f. carrier amplitude modulated by a first audio frequency waveform and an r.f. carrier amplitude modulated by a second audio frequency waveform which is distinguishable from the first and which may be employed as a means for identifying a particular transmitter. The composite, sequentially transmitted signal may be varied in terms of the individual signal transmission sequence, the duration of the individual signals, overall composite signal repetition rate and the frequency of the second audio waveform. Various combinations of signal variations may be employed to transmit different information.

Abstract: A receiver and transmitter are provided for a distress incident locating telecommunications system. The receiver is a superheterodyne AM receiver which applies the received distress transmissions to a normally unlocked phaselock loop which locks onto the unmodulated carrier signal portion of the distress transmission. The duration of the phaselock loop being locked, and unlocked immediately after being locked, are measured and compared to predetermined values to find a match. Each of the predetermined values corresponds to an item of information, and if a match is found, the receiver indicates it. The receiver is also capable of extracting audio information present in the distress transmission. The transmitter generates three signals which can be applied to a transmitting antenna. These signals are a radio frequency carrier signal, and a carrier signal modulated by a distress waveform or by an audio signal.

Abstract: In an emergency locator transmitter of a type wherein a standard distress signal is transmitted following a distress incident, the distress signal is encoded with data identifying the absolute time of the incident or the amount of time that has elapsed since the incident occurred. Distress waveform modulation of the carrier is periodically interrupted for insertion of the time signal. In a preferred embodiment, wherein the distress signal includes information burst signals that are periodically transmitted, e.g., every 50 seconds, timing pulses generated synchronously with the burst signals are supplied to a divider circuit for division by a predetermined integer to develop extended time base pulses, e.g., one hour pulse intervals. The extended pulses are accumulated in a binary counter and combined with the information burst signals.

Abstract: During a distress call, a distress location transmitter 10 generates a high frequency carrier signal 40 that is modulated by a predetermined distress waveform characteristic 29. The classification of user associated with the distress call is identified by periodically interrupting modulation 42; user classification is determined by the repetition rate of the interruptions, the interruption periods, or both.