Abstract: This circuit provides output detection pulses in response to interrogation signals for transponder systems which require a high degree of sensitivity and a low degree of false alarms. This circuit includes a tracking arrangement which monitors the level of noise and adjusts a control signal to exclude noise below a certain threshold. A comparator generates detection pulses in response to the input interrogation signals and the control signal. As a result, detection pulses are produced only for interrogation signals on a one-for-one basis. At the same time, the circuit adjusts its sensitivity so that low power interrogation signals (sufficiently above the noise level) may be accurately detected without responding excessively to noise. In addition, an active clamp circuit increases the gain and sensitivity of the circuit by clamping the noise level to approximately a ground state. The circuit is totally insensitive to the interrogation pulse amplitude and relatively insensitive to the interrogation pulse rate.

Abstract: A secure identification system for identifying a potential target in a battlefield environment as being either a friend or a foe is disclosed. An interrogator produces two interrogation pulses, such as laser flashes, aimed at the target and separated from each other by a randomly determined period of time. The target detects the two interrogation pulses, measures elapsed time between the two pulses, and prepares a reply signal for transmission which is controlled by the elapsed time. Frequency, pulse width, and transmission delay parameters are each controlled in a substantially random, but predetermined manner in response to the elapsed time. The interrogator has a receiver and qualifier which receive reply signals and define expected values for the controlled parameters. An indication is provided concerning whether the target represents a friend or a foe based on received reply signals at the interrogator.

Abstract: A solar energy system in which a heat transferring liquid captures heat in solar collectors and stores it in a storage tank is disclosed. A pump moves heat transferring liquid from the storage tank to the collectors and into a drain-back module only when a predetermined activation temperature is achieved. The pump then inactivates allowing heat transferring liquid within the collectors to heat. When the pump initially inactivates, a siphon or draining cycle is formed which moves heat transferring liquid from the drain-back module to the storage tank. Gas within the storage tank replaces heat transferring liquid in the collectors through the drain-back module to achieve drain-back. However, the siphon or draining operation must first cause heat transferring liquid within the drain-back module to fall below a drain-back feed point. Thus, the solar energy system delays drain-back until after the siphon or draining operation is completed.

Abstract: A pulse width and amplitude control apparatus wherein an analog Doppler to digital pulse converter provides pulses to the up input of an up/down counter in the presence of a noise input or a Doppler input, and a second analog Doppler to digital pulse converter applies pulses with greater frequency to the down input of the up/down counter when a Doppler signal exceeding a predetermined threshold is present, so that a low or no signal condition increases and a high signal condition decreases the transmit pulse envelope.

Abstract: In conjunction with a doppler radar of the type having early and late gate, leading edge tracking apparatus (i.e., tracking the leading edge of the pulse reflected by the target), circuitry for switching from a leading edge tracking mode to a doppler count tracking mode and logic circuitry for counting doppler signals and changing the range a predetermined amount per signal to estimate the range of the leading edge of a target when the leading edge is obscured by transmitter pulse feedthrough to the receiver.