Abstract: A method and apparatus for simultaneously operating two diathermy treatment heads in close proximity without interference caused by phase and frequency differences. Each diathermy head has a drive circuit powered by a master oscillator providing RF energy. Each head can be used alone with RF drive from its own oscillator. When the heads are to be used in close proximity, they are coupled by coaxial cable, and one oscillator is automatically disabled to permit the other oscillator to furnish the RF drive for both systems. The RF drive is then coherent in phase and frequency in both systems, so the two diathermy heads do not "fight" each other.

Abstract: Disclosed is an electronic channel selector comprising a plurality of diodes in series with a plurality of crystals, each diode/crystal connection defining one channel of the ten channel crystal-controlled oscillator. Non-enabled diodes are maintained in a reverse bias condition, preventing the associated crystal from oscillating in the oscillation circuit. The diode corresponding to the selected channel is forward biased into conduction permitting the associated crystal to control the oscillator circuitry providing the desired frequency output. When the selected diode is forward biased and begins conducting current, it conducts current through a path which provides a tuning voltage which may advantageously be utilized in a transmitter exciter filter or receiver preselector. A binary switch is manually set for the desired channel and produces a binary coded output. A binary-to-decimal decoder provides a single enabling output which is determined by the binary code supplied from the binary switch.

Abstract: An improved frequency control system for radio apparatus is provided, which is especially advantageous for employment in portable, battery powered, multichannel, radio transceivers.The system involves both individual and combinational type improvements relating to the constructional and operational aspects of transceiver equipment. Some salient features of the system include digital frequency synthesizer circuitry having a frequency and phase locked loop employing a voltage controlled oscillator, out-of-band selection detecting and transmit inhibit signal generating circuitry, and filtering and amplifying circuitry employing voltage controlled tuning and improved wide-band inter-stage coupling for supplying frequency controlling signals for both a receiver and a transmitter from a common excitation source.

Abstract: A low level modulation circuit for use in a radio transmitter obviates the needs for an audio transformer device heretofore required for high signal level modulation of the final stages of a multistage radio frequency amplifier by modulating an initial amplifier stage using a conditioned, low level modulation signal, but yet eliminates additional distortion and noise imposed upon the modulated audio signal by the initial and intermediate amplification stages, through the use of a single, negative feedback circuit.

Abstract: Especially simple structure for an electrical transformer device provides cost effective fabrication thereof and offers improved operating performance particularly in a radio transmitter circuit for coupling high levels of radio frequency energy from the output of a radio frequency amplifier to an antenna system. One winding of the transformer is formed from a single, unitary, tubular member arranged into a U-shaped configuration which includes a pair of spaced sets of openings therein for the two-fold purpose of allowing efficient threading of a secondary winding therewithin and to improve air cooling characteristics of the device. A second winding comprises a wire passed through the interior of the tubular member, and a number of cylindrically shaped magnetic elements are sleeved over the tubular member to enhance the mutual inductive coupling between the windings.