Tft, Inc.

Time and Frequency Technology Inc.

Elf Engineering, Ltd.

Competive Technologies, Inc.

John James

Joseph C Wu

Calvin Eckels

Yee-Shing Law

A portable FM stereo RF transmitter having an audio plug extending therefrom directly or via a cable and which mates with the earphone or output jack of an audio source such as a portable battery operated CD or tape player and having no external antenna. The portable RF transmitter modulates audio signals from the audio source onto an FM carrier and transmits them to an FM receiver mounted on a headset worn by a user. The RF transmitter uses its own ground circuit and the ground circuit of the audio source as two elements of a short dipole. The two ground circuits are electrically isolated at RF by an RF choke but connected together at audio frequencies by the low impedance of the choke at audio. The choke's leakage inductance also reduces the capacitive reactance of the dipole antenna for better power dissipation. A transformer coupling the RF output to the dipole transforms the impedance of the dipole to a value closer to the output impedance of the RF transmitter. A phase lock loop controls the carrier frequency to remain in the center of the channel even as the battery voltage drops.

Small, battery operated RF transmitter for portable audio devices for use with headphones with RF receiver

A low power, frequency-mode magnetometer. The magnetometer includes an LC oscillator, a bias resistor and a polarity switch. The LC oscillator produces an output signal having a variable frequency indicative of both a magnitude and a polarity of a magnetic field. The LC oscillator includes an inverting amplifier and a Pi network including an inductor and two capacitors. The inductor is realized as a coil wound about a high permeability, low hysteresis, core material that has been longitudinally cut. The inductor is coupled between an input node and an output node, as is the inverting amplifier. The inverting amplifier has a first trigger voltage and a second trigger voltage, which are symmetrically located with respect to one half of a DC bias voltage. The bias resistor is coupled between the input node of the LC oscillator and a first node and controls the DC bias current to the inductor. The polarity switch switches the first node between ground and the bias DC voltage.

Low power, frequency-mode magnetometer

A UHF transmission frequency oscillator generates a UHF radio signal that is frequency modulated by a program signal. The voltage applied to a control voltage input of the UHF transmission frequency oscillator controls the transmission frequency. A sample of the UHF transmission frequency signal is heterodyned with the output of a crystal controlled reference frequency oscillator to generate a frequency difference signal. A voltage controlled VHF radio signal generator produces a VHF signal frequency modulated by the program signal. A phase detector receives the frequency difference signal and the VHF signal frequency modulated by the program signal and therefrom applies a voltage to the control voltage input of the UHF transmission frequency oscillator for the transmission of a UHF radio frequency signal frequency modulated by the program signal. The VHF voltage controlled generator has VHF programmable frequency dividers, which are pre-settable, to establish the VHF radio transmission frequency. The output of the VHF voltage controlled generator is phase locked through the phase detector with the crystal controlled reference oscillator for the stabilizing of the output transmission frequency of the UHF transmission frequency oscillator.

Method of and apparatus for generating a frequency modulated ultrahigh

An attention signal receiver in which emergency broadcast transmissions are detected from various locations. A scanning circuit sequentially activates means to produce a plurality of oscillating frequencies which mix or beat with the incoming r.f. signals. An attention signal is a two tone signal that includes both a 960 H.sub.z frequency signal and a 853 H.sub.z frequency signal. The audio stage of the receiver is connected to a two tone decoder that passes only a 960 H.sub.z signal and a 853 H.sub.z signal. A squelch circuit is also connected to the audio stage of the receiver. Connected to the output of the tone decoder is a one second time delay circuit and a ten second time delay circuit. If an attention signal is detected for a period of time in excess of 1 second, the one second time delay circuit stops the scanning of the scanning circuit to lock in the receiver to the first carrier detected with an attention signal. The ten second time delay circuit normally disables the squelching circuit. If the detected attention signal continues for a period of time in excess of 10 seconds, the ten second time delay circuit enables the squelch circuit to operate an alarm.

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Los Gatos, CA, United States of America

John James