Systems for preventing the operator of an aircraft radio from beginning a transmission while someone else is transmitting on the same radio frequency channel, which is known as "stepping on" the first transmission. In one form, a "step-off" device in accordance with the invention is internally connected to the radio receiver circuitry to sense when a particular selected radio frequency channel is in use. An SCR is interposed in series with the transmitter push-to-talk (PTT) line, and the SCR is ...

A radio transceiver has a single reference oscillator and a receiving frequency synthesizer and a transmitting frequency synthesizer. The synthesizer frequencies are selected so that the receiving intermediate frequency and a transmitting intermediate frequency (produced by the transmitted frequency mixing with the received frequency) are spaced widely apart. Thus, any beat note between the two intermediate frequencies is outside the passband or filter bandwidth in the receiver circuit.

The high power (10-1000 W) modulated carrier of a noisy transmitter is attenuated and amplitude limited and is used to control a power oscillator which regenerates the carrier and modulations without the loss of power. The power oscillator is slaved in frequency to the amplitude limited and attenuated signal, and it follows any phase or frequency modulation present thereon. Noise components appearing on the original carrier fall outside of the information passband of the power oscillator loop an...

The antenna of a transceiver couples through a low pass filter to the input port of a high pass filter network. The high pass network is designed to reflect a very high impedance to its input port when its output port is at ground potential. The transmitter portion of the transceiver couples to the input port of the network with the receiver coupling to the network output port. A semiconductor diode couples from the output port to ground potential. In the receive mode the combination low pass an...

A switching circuit for use in a transceiver whereby a unidirectional mixer may be used for both transmitting and receiving. The circuit allows the combination of the high gain obtainable from unidirectional active mixers with the versatility of bidirectional operation.

An audio transmission reception assembly has a hollow tubular conduit arred to conduct audio messages from a source within a waterproof enclosure, which may be worn by attachment to the clothing of the user, for conduction to the entrance to the ear canal of the user. The tubular conduit has a capillary portion connected adjacent to the source of the audio messages which renders the conduit virtually waterproof even when subjected to underwater conditions. An audio responsive means is contained ...

A solid-state switch for coupling an antenna to either a transmitter or a receiver. The switch includes a pair of oppositely poled diodes and a low voltage power supply connected between the diodes for providing a forward biasing voltage to the diodes. Reverse biasing voltage to stop RF current flow through the diodes is provided by the RF signal itself by means of a voltage doubler. The same voltage doubler and a power detector reverse bias the receiver diode during overload conditions.

A simplex radio transmitting and receiving apparatus, has a transmission blocking means which prevents selection of the transmitting mode of the apparatus if a signal of predetermined strength is being received by the apparatus at the time the press-to-talk key is operated. An over-ride circuit enables the blocking means to be disabled in an emergency or if another transmitter has been left operating in error. The over-ride circuit can be activated by, for example, repeated operation of the pres...

An oscillator is controlled so that it produces the correct frequency in the transmitting condition, and so that it produces a slightly different frequency in the receiving condition. This is achieved by a circuit which supplies a first control voltage to the oscillator for transmitting and which supplies a second and different control voltage to the oscillator for receiving. This second and different control voltage causes the oscillator frequency in the receiving condition to be different so t...

An antenna device corresponds to a plurality of radio communications systems and frequency bands, can simultaneously carry out a reception and a transmission of different radio communications systems, and is capable of using antenna diversity by a simple construction. An antenna device comprises a first antenna matching with first, second, and third frequency bands, a second antenna matching with the third frequency band, a diplexer and the like. For signals of the first frequency band, a high-f...