Iimorrow, Inc.

Garmin At, Inc.

Stephen A Roth

Thomas Lee Mosher

Roar Berg-johansen

A method is disclosed for optimally adjusting the received bit detection threshold in a digital communication system, such as a TDMA system that is characterized by very short duration burst transmissions. In one embodiment of the invention, a half-duplex radio modem is used for transmission and receipt of messages for airborne and ground-based Automatic Dependent Surveillance-Broadcast (ADS-B) service. A feedback path is provided for in the transmission/receiver unit to provide the transmission signal to the receiver path. A bit detection threshold adjustment circuit receives the transmission signal. The circuit digitizes the analog baseband signal, detects the positive and negative peak values and calculates a peak-to-peak deviation value to define the bit detection threshold value.

Bit detection threshold in a TDMA burst communication system

A dual function antenna system and method. A system is provided for using a single antenna for both the reception of low frequency navigational signals, such as LORAN-C, and high frequency communications signals in the VHF region. The antenna is at a remote location from a low frequency receiver and a high frequency transceiver. Both the low frequency and the high frequency signals are coupled to the receiver and transceiver, respectively, over the same transmission line at one end thereof. A preamplifier is provided at the location of the antenna to increase the strength of the low frequency signal applied to the transmission line. A high pass filter is provided to couple the antenna and the transmission line and prevent feedback from the output of the preamplifier from reaching its input. The other end of the transmission line is coupled to the high frequency transceiver by a high pass filter, and to the low frequency receiver by a low pass filter. The preamplifier is supplied with DC power over the transmission line, and includes a current regulator so that the preamplifier may be used with a wide range of supply voltages.

Combined low frequency receive and high frequency transceive antenna

A magnetometer and method for measuring magnetic field strength particularly adapted for use in an electronic flux gate compass. A core of magnetic material in the shape of a toroid is coupled to a drive coil and to two sense coils oriented along orthogonal axes. A current limited, current source coupled to the drive coil periodically saturates the core, drives the core out of saturation at an intermediate current level, and saturates the core again. Each sense coil is coupled to a sense circuit which measures the current in the sense coil induced by the periodically changing flux density in the coil resulting from an external magnetic field coupled to the sense coil, produces a dc feedback signal to cancel out the external magnetic field, and provides the dc signal as an output representative of the external magnetic field strength along the axis of the sense coil. The dc signal is produced by synchronously detecting the amplified ac current in the sense coil. Low pass filters are provided to eliminate ac components from the magnetometer output.

Low power, high accuracy magnetometer and magnetic field strength

A variable attenuator comprises a plurality of attenuator stages connected in series along a transmission line signal path. Each attenuator stage comprises a resstive pi-section attenuating pad which may be selectively inserted into the signal path to increase attenuation along the path. Each series element of the pad is selectively inserted or removed from the signal path by opening or closing a parallel connected switching device, while each shunt element of the pad is selectively connected to or disconnected from ground by closing or opening a corresponding series connected switching device. The switching devices each comprise an NPN bipolar transistor and a PNP bipolar transistor, the emitter of each transistor being coupled to the emitter of the other and the collector or each transistor being connected to the collector of the other, to provide a low impedance AC signal path from collector to emitter when the transistors are active.

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Aumsville, OR, United States of America

Stephen A Roth