A multifunction ultra-high frequency circuit and bidirectional transmission means using such a circuit. The circuit according to the invention comprises a directional coupler, two diodes, a transistor and an access connected to the diodes. The state of the transistor defines several functions of the circuit: modulation, mixing and transmission-reception separation. Application to half-duplex transmission.

Communication of electric signals between a control board mounted on a steering wheel but held in stationary state irrespective of a rotation of the steering wheel and an electric controller disposed at a position remote from a steering mechanism. The control board is supported by a steering drive shaft through a toothed wheel mechanism, so that it remains stationary regardless of a rotation of the shaft. The control board and the electric controller are electrically coupled to each other through a combination of slip rings and brushes, a pair of coils, or two pairs of coils. The control board and the electric controller include each an FSK modulation circuit, an FSK demodulation circuit and a microprocessor for controlling transmission or reception of the electric signals. Key inputs on the control board are encoded by the control board and then transmitted to the electric controller. The electric controller decodes the received code and then renders operation instructions to load-vehicle equipments.

An improved proximal cable-less communications system using at least two receivers is described. The system is significantly improved by eliminating the sidetone which can occur in full duplex systems. Components are placed in the receivers, between the mixer components and the components which detect the information encoded in the signal at the intermediate frequency, which function to cancel out the detrimental affect of those signals containing information derived from the modulation of the local oscillator of the receiver device.

An improved proximal cable-less communications system using at least two receivers is described. The system is significantly improved by utilizing an intentional signal path for the local oscillator signal to be radiated while maintaining the architecture of each receiver and the proximal cable-less communications system. The effectiveness of radiation can be increased by extending the length of the electrical interconnect which connects the local oscillator to the mixer. In addition, the effectiveness of radiation is increased by magnetically coupling the electrical interconnect which connects the local oscillator with the mixer with the electrical interconnect which connects the antenna and the mixer. By coupling the two electrical interconnect, the signal output by the local oscillator is induced on the electrical interconnect between the antenna and the mixer. The coupling is set such that the signal induced travels along the electrical interconnect and is radiated out of the antenna.

A bidirectional level shifting interface circuit has first and second I/O ports and an FET with a drain-source channel connected between the first and second I/O ports. The first I/O port is connected to an I/O port of a first digital circuit operating at a relatively low supply voltage, and the second I/O port is connected to an I/O port of a second digital circuit operating at a relatively high supply voltage. This channel passes communication signals in each direction between the first and second digital circuit. A latching circuit comprising a P Channel FET is biased by the relatively high voltage supply, has an output connected to the second I/O port, and has a control input. The interface circuit further comprises an inverter circuit having a control input connected to the second I/O port and an inverted output connected to the control input of the latching FET such that when the second I/O port exhibits a binary one voltage caused by the first digital circuit, the inverted output exhibits a binary zero voltage to activate the P Channel FET to latch the second I/O port at sufficient voltage to drive the second digital circuit at binary one level.