Abstract: This separating device is provided with a transmitting filter and a receiving filter. Each of the transmitting and receiving filters comprises a variable capacity diode and a resonant element, and compose a band elimination filter. Each of the elimination bands of the transmitting and receiving filters can be adjusted by changing the capacity value of each variable capacity diode. The elimination band of the transmitting filter is adjusted so as to coincide with the receiving frequency of the communication channel currently used. The elimination band of the receiving filter is adjusted so as to coincide with the transmitting frequency of the communication channel currently used.

Abstract: An antenna interface unit (AIU) for providing low power loss, fault tolerant connectivity between multiple transmitters and an antenna, and between multiple receivers and the antenna. The antenna interface unit also eliminates single point failures in a transmit/receive (T/R) mechanism. The antenna interface unit includes (a) a power combiner/splitter connectable to the antenna; a receive channel connected to the power combiner/splitter; and a transmit channel connected to the power combiner/splitter. The transmit channel is a different channel from the receive channel. The receivers are connectable to the antenna via the receive channel and through the power combiner/splitter. The transmitters are connectable to the antenna via the transmit channel and through the power combiner/splitter. Different variations of the receive channel and the transmit channel are provided by using different combinations of power combiners and power splitters.

Abstract: The present invention relates to an arrangement for transmitting a radio-frequency signal at two different frequency bands and for receiving at two different frequency bands. The arrangement can be applied for instance to a transceiver of a radio communications system operating at two different frequency bands, or to a transceiver meant to be used in connection with two different radio communications systems. One of the ideas of the invention is that one and the same filter (72), belonging to the RF front end of the antenna circuit, is used for filtering interference from at least two signals located at different frequency bands, in which case the number of filters (72, 75) can be reduced. By means of the solution suggested in the invention, also the number of controllable switches (73) provided on the signal path of the RF front end can be minimized.

Abstract: A method and device for modifying a frequency range of a radio transceiver by mixing a signal to be transmitted by the transceiver with the output of a local oscillator so as to change the frequency thereof to a desired frequency for transmission and by mixing a received radio transmission with the output of a local oscillator so as to change the frequency thereof to a frequency within the nominal reception band of the transceiver.

Abstract: A switching device is disclosed having a ring circuit with four nodes and four switching elements which selectively interconnect the four nodes. A first compensation branch inter-connects a first pair of mutually opposing nodes, and a second compensation branch inter-connects a second pair of mutually opposing nodes. The first compensation branch generates a first parallel resonance in conjunction with a first non-conducting one of the four switching elements, and the second compensation branch generates a second parallel resonance in conjunction with a second non-conducting one of the four switching elements. The first parallel resonance is connected in parallel to a conducting one of the four switching elements, and the second parallel resonance is connected in parallel to the conducting one of the four switching elements. Each compensation branch includes an inductor which forms the respective parallel resonances in conjunction with a capacitance of a non-conducting switching element.

Abstract: A pair of filter units directs incoming signals from an antenna and outgoing signals to the antenna. One of the filter units blocks the outgoing signals and passes the incoming signals while the other of the filter units blocks the incoming signals and passes the outgoing signals.

Abstract: An antenna amplifier utilizes integrated dual duplex filters having a first filter branch for allowing through a transmitter band (Tx) between an uplead and an antenna, a second filter branch (Rx1) for allowing through a receiver band (Rx) from the antenna to an output element (3), a third filter branch for allowing through the receiving band (Rx) from an input element (4) to the uplead, and a low noise amplifier whose input is connected to the output element and whose output is connected to the input element. The low noise amplifier (LNA) is preferably both constructed and connected by means of filter-technical and circuit board-technical methods.

Abstract: An antenna unit in which fine antenna characteristic can be obtained when the antenna is contained/pulled out. When the second antenna (9) is contained, the second antenna is electrically disconnected from the feeding circuits (5, 7) by the antenna cover (13), so that only the first antenna (8) operates as antenna. On the other hand, when the second antenna is pulled out, the first antenna is compressed by the antenna stopper element (21) and the electrical length is varied, so that only the second antenna operates as antenna. As a result, fine antenna characteristic can be obtained when the antenna is contained/pulled out.

Abstract: The present invention provides increased geographical coverage and system capacity for mobile/portable radio transceivers using adjacent and typically separate radio communication frequency bands. A radio that transceives in just one frequency band is adapted to provide a configurable duplexing arrangement to permit communications in extended frequency bands. Duplexing circuitry is connected between the radio antenna and the radio transmitter and receiver. Depending upon the mode of operation of the radio transceiver, switches are selectively operated for variously configuring the antenna, duplexer circuitry, receiver, and transmitter to permit communications in a first or a second set of transmit/receive frequency bands. In one preferred example embodiment, only a single duplexer is employed connected to the antenna and transceiving circuitry through plural switches.

Abstract: A transmitting-receiving switch-over circuit arrangement for a transceiver includes a transmitter terminal (TX) and a receiver terminal (RX) connected by respective transmitting and receiving circuit sections to a circuit junction point (P) that is coupled to an antenna terminal (ANT). A controllable semiconductor switch (D1, D4, D6) is connected to the transmitting circuit section. A further controllable semiconductor switch (D2, D3, D5, D7) is connected to the receiving circuit section. Control signals are applied to the semiconductor switches so that at least the semiconductor switch connected to the receiving circuit section is controllable independently to assume any one of three stages, namely: fully passing the received RF-signal, fully blocking the received RF-signal, and attenuating the received RF-signal.

Abstract: The object of the invention is a radio communication transceiver, in which the low noise pre-amplifier and mixer of the receiver and the power amplifier, directional coupler and the mixer of the transmitter are integrated in connection with the filter section. The active components are integrated with the filter so that the entity forms one component on the circuit board of the telephone.

Abstract: A transmitting and receiving apparatus including a transmitting system and a receiving system which prevents fluctuations in insertion losses caused by changes in transmission power, while obviating the need for the provision of a battery and a current control circuit for providing a switching current, and suppresses losses in the transmission system so as to improve the power efficiency, and also decreases the cost of parts. The transmitting and receiving apparatus having a transmitter and a receiver sharing a single antenna is configured as follows. A circulator is provided at a feed point of the antenna between the transmitting system and the receiving system. Also, a changeover switch is disposed between a terminating resistor connected to ground and a point where the circulator and the receiver are connected so that the changeover switch can be automatically switched to the terminating resistor in response to input power supplied from the transmitter during transmission.

Abstract: A method and apparatus for object identification which includes a portable electronic tag reader having a transceiver capable both of reading identification information from electronic tags and transmitting collected information to a base unit for remote analysis. The system of the present invention utilizes the same transceiver to receive information from the base unit and write data to read/write electronic tags. The system of the present invention includes a transceiver for generating a modulated or unmodulated radio frequency interrogation signal, a receiver for detecting a return signal from an electronic tag and a signal processor for processing the return signal. A modulator within the portable unit combines the identification data with the radio frequency interrogation signal for transmission to a base unit through a wireless local area network. A demodulator within the portable unit extracts data and commands received from a base unit for local processing or transfer to a read/write electronic tag.

Abstract: A dual band filter network for a radio communication apparatus is provided. The network has an antenna (212) for receiving and transmitting signals from a first frequency band and a second frequency band. The network has a first duplex pair (202) including a first transmit filter (204) including a first passband and stopband. The first duplex pair (202) also includes a second receive filter (206). The first filter (204) presents a consistent phase in the second passband due to the wide frequency separation between the first filter (204) and the second filter (206). The network has a second duplex pair (202') with similar characteristics as the first duplex pair (202). The network also has a switching circuitry (210) controlled by a switch control voltage (214) for selecting the appropriate filter circuitry. The network can be provided in a small sized, low cost package that also offers improved insertion loss performance.

Abstract: An isolation circulator network includes three circulators and a 180 degree ybrid coupler for isolating an RF transmitter from a nearby RF receiver. The isolation circulator network comprises: a first circulator for transforming a first RF signal, RF.sub.1, into a second RF signal, RF.sub.2 and a third RF signal, RF.sub.3 ; a second circulator for throughputting the third RF signal; a third circulator for transforming the second RF signal into a fourth RF signal, RF.sub.4, and a fifth RF signal, RF.sub.5, and for throughputting a sixth RF signal, RF.sub.6 ; and a 180-degree hybrid coupler which provides a seventh RF signal, RF.sub.7 in response to receiving the third, fifth, and sixth RF signals, where RF.sub.7 =(RF.sub.5 -RF.sub.3 +RF.sub.6).

Abstract: In a switch semiconductor integrated circuit, a switch for high frequency signal is constituted by four field-effect transistor stages connected in series to the first to fourth signal paths arranged in a ring shape and two field-effect transistor stages connected which are in a shunt position with respect to the signal paths such that two signal paths are positioned between two field-effect stages which are opposite to each other. At this time, the same voltage is impressed to the signal paths which are in a position opposite to each other among four signal paths, and the control voltage which are complementary to each other is impressed to the adjacent signal paths.

Abstract: A transmitter/receiver apparatus employed with advantage in a radio communication system for radio transmission and reception of frequency division multiplexed or time-division multiplexed signals of the frequency division duplex system on switching between plural antennas includes a plurality of antennas for radio transmission/reception of the reception and transmission signals, a switch for switching between the antennas, a plurality of antenna duplexers connected to the antennas via the switch and having respective different frequency bands, a transmission unit connected to the antenna duplexers, a reception unit connected to the antenna duplexers and a control unit for controlling the switch, transmission unit and the reception unit. The control unit controls the switch so that an optional one of the antennas will be connected to the antenna duplexers of the frequency band corresponding to the frequency used in radio communication solely by the switching.

Abstract: A small radio communication unit which requires no antenna adjustment is provided by using small chip antennas whose gain is not degraded and which have a wide bandwidth.

Abstract: A changeover switch switches connection between an antenna and a transmitter amplifier and connection between the antenna and a receiver low noise amplifier, from one to the other. A first wire having characteristic impedance of 50 .OMEGA. connects the antenna and the changeover switch. A receiver matching circuit matches input impedance of the receiver low noise amplifier with the output impedance of the transmitter amplifier. An antenna side matching circuit matches the input impedance of the receiver low noise amplifier, which is matched with the output impedance of the transmitter amplifier by the receiver matching circuit, and the output impedance of the transmitter amplifier with the characteristic impedance of the first wire. The transmitter amplifier is connected with the changeover switch via a first coupling capacitance, and the receiver matching circuit is connected with the changeover switch via a second coupling capacitance.

Abstract: In a mobile communication device, a power amplifier amplifies the power of a signal to be transmitted. A transmitter filter limits the frequency band of the amplified signal to a predetermined frequency band for transmission. The signal limited in frequency band is transmitted via an antenna. Output power control circuitry controls the output power of the signal to be transmitted and has an output power sensor and an automatic power control circuit. The output power sensor succeeds the transmitter filter in the direction of flow of the signal to be transmitted, and senses the output power of the signal. The automatic power control circuit controls the gain of the power amplifier such that the output power sensed by the output power sensor coincides with a preselected reference value.

Abstract: A mobile terminal device for telecommunications includes a switch circuit which comprises two field effect transistors connected in series to an input terminal, an output terminal and a common input/output terminal respectively, for AC signals. The switch circuit includes control devices which are cyclically shifted for the two transistors. The control devices are formed by pulsed multiplexed bias voltages of amplifiers which produce and receive the AC signals, and by a logic OR-circuit of diodes and resistor. The voltages on the terminals of the diodes are connected between the gate and source of the transistors for their cyclically time-shifted control.

Abstract: A transmit/receive radio set having a transmitter output stage, a receiver input stage, and an antenna switching device for change-over between transmission and reception by a single antenna. Two impedance transformers are provided at the output of the transmitter output stage. A switching circuit effects a change-over of the output impedance of the transmitter output stage during transmission and reception by controlling the impedance of at least one of the impedance transformers.

Abstract: A complimentary switched amplifier transceiver (10) is provided which offers performance advantages and reduces system complexity over conventional half-duplex transceivers by using complimentary switched amplifiers for eliminating switches. Power output to a channel transition (31) from a transmit amplifier (26) is not degraded by a switch insertion loss in a transmit mode. Receiver noise figure is not degraded due to the switch insertion loss from the channel transition (31) to a receive amplifier (27). Switch devices and their associated control lines are eliminated, reducing circuit complexity for complimentary switched amplifier circuits such as a combined amplifier switch (12) and a first bi-directional amplifier (22).

Abstract: In a digital mobile radio apparatus according to the present invention, a duplexer for connecting a transmitter and a receiver to a common receiving/transmitting antenna is constructed from an isolator and a receiving band-pass filter. The receiving band-pass filter prevents a transmitted wave from entering the receiver. Impedance matching is effected so that the isolator can prevent a received wave from entering the transmitter while suppressing the entrance of signals radiated from other mobile units in the same transmitting frequency band but at a different operating frequency.

Abstract: In an antenna duplexer, one antenna is used by switching transmission signals and reception signals having different frequencies. The antenna duplexer includes a high-frequency switching circuit and a band-pass filter. The high-frequency switching circuit supplies the transmission signals from a transmission part to the antenna. The band-pass filter outputs the reception signals outputted from the antenna to the predetermined receiving circuit. In the band-pass filter, the frequency characteristic is selected and set to impress the frequency of the transmission signals, and simultaneously the reflected wave generated at the input end so that impedance increases at the frequency band of the transmission signals.

Abstract: A duplexer usable for both transmission and reception in a mobile communication apparatus such as a car phone has both its transmission section and reception section mounted on a single substrate. The transmission section is connected between an input terminal and an antenna terminal and includes an isolator and either a circuit having only inductors and capacitors or a trap circuit having a dielectric resonator and an inductor and a II-type low-pass filter having an inductor and capacitors. The reception section is comprised of a filter using dielectric resonators.

Abstract: A communication apparatus for use in a portable telephone is disclosed which has a transmit-receive common amplifier for amplifying a transmitted signal or received signal, and a mixer for frequency-mixing the transmitted signal or the received signal with a local oscillator output, wherein connection between the mixer and an input side of the amplifier and connection between the mixer and an output side of the amplifier are made by means of respective signal-path selector switches. During reception, a deep bias is applied to an FET of the transmit-receive common amplifier to reduce current consumption, and during transmission, a shallow bias is applied to the FET of the transmit-receive common amplifier for increased output.

Abstract: What is described is a commonly coupled high frequency transmitting/receiving switching module (100). The switching module (100), has a transmitting circuit (102), a receiving circuit (104), an antenna circuit (106), an external circuit (108), a coupling circuit (110) and control circuits (124, 126). The switching module may be switched between one of four circuit paths (202, 204, 206, 208) each path incorporating an integral harmonic filter (210, 212). This structure is adapted for use in a multi-layer ceramic integrated circuit, and provides the advantage of minimizing current consumption with a minimal number of components.

Abstract: A radio system and interference cancellation system for use with the radio system include a receiving radio and a transmitting radio which are coupled to a common antenna. A reference coupler provides a reference signal in response to the signal transmitted by the transmitting radio and provides the reference signal to a vector modulator and a synchronous detector. A receiver coupler is responsive to the transmitted signal which is reflected by the antenna and to the signal which is desired to be received and provides a received signal containing an interfering signal component and a desired signal component. An error coupler samples the received signal which includes any residual interfering signal component after cancellation, and provides an error signal to the synchronous detector. The synchronous detector compares the reference signal with the error signal and provides a detector output to the vector modulator.

Abstract: The antenna switch of the present invention switches from a portable radio's internal antenna to an external, vehicle adapter antenna. The second antenna is part of the vehicle adapter that supplies DC power to the vehicle adapter. A 1/4-wavelength transformer couples the internal antenna to the portable radio's transceiver. Diodes couple transformer and antenna to ground. A 1/2-wavelength transformer couples the vehicle adapter to the transceiver. When the portable radio is connected to the vehicle adapter, DC power is supplied to the diodes causing them to appear as a short thus making the first transformer appear as an open circuit. This causes a signal from the transceiver to be conducted to the second antenna on the vehicle adapter.

Abstract: Disclosed herein are methods and apparatus for generating digital receiver and transmitter AGC values for a spread spectrum transceiver. A method includes the steps of (a) integrating the power of a received and sampled signal; (b) calculating a logarithm of the received integrated power; (c) subtracting a predetermined reference value from the logarithm of the power to generate a first error signal; (d) filtering the first error signal; (e) comparing the filtered first error signal to a predetermined first threshold; (f) incrementing or decrementing a first counter value and resetting a filter accumulator as a function of the result of the step of comparing; and (g) converting the first counter value to an analog voltage for controlling the gain of a spread spectrum receiver amplifier. The logarithm is preferably the second logarithm of the power. The method further includes generating a transmitter AGC value.

Abstract: A radio receiver-transmitter apparatus equipped with a signal changeover switch which is capable of properly dealing with a high-power radio frequency signal and ensuring a desired insertion loss and superior isolation characteristic. The switch has a signal input terminal, a signal output terminal and a signal input-output terminal, and comprises a 1st FET unit connected to the input terminal and the input-output terminal, a 2nd FET unit connected to the input terminal and the ground, a 3rd FET unit connected to the output terminal and the input-output terminal, and a 4th FET unit connected to the output terminal and the ground.

Abstract: In a portable satellite communication equipment including a transponder for transmission and reception, and an antenna portion which is electrically coupled to the transponder, the antenna portion has first and second common flat antennae. The first and the second common flat antennae are common to both the transmission and the reception and are foldably coupled to each other.

Abstract: A switch circuit for a cellular radiotelephone operable in a TDMA communication scheme. The switch circuit is disposed upon a plurality of tandemly-positioned ceramic substrates having transmission lines disposed upon one of the ceramic substrates. The switch circuit alternately connects transmitter circuitry to an antenna or receiver circuitry to the antenna, thereby alternately to permit transmission or reception of signals generated by, or received by the radiotelephone. Because circuits disposed upon ceramic materials are of low insertion losses, the switch circuit is advantageously utilized to form a portion of the radiotelephone.

Abstract: A transmitting circuit is connected to an antenna via a first diode. The antenna is connected to a receiving circuit with the circuit including a strip line and a second diode. Two diodes are turned ON by applying a positive voltage to a first control terminal. In this state, a signal from the transmitting circuit is transmitted from the antenna. The transmission signal is not transferred to the receiving circuit side due to a series resonance circuit with the inductance of the second diode and a capacitor. When the high-frequency switch is used for reception, a positive voltage is applied to a second control terminal. The voltage is divided by a resistors respectively connected to the diodes in parallel, and applied to the diodes as a backward voltage. And hence, the diodes are surely maintained in the OFF state. The isolation between the transmitting circuit and the antenna is improved by a parallel resonance circuit with the capacitance of the first diode and a inductor.

Abstract: A wireless communication system includes a plurality of stations each having a plurality of antennas. A first packet, containing a training signal portion is transmitted from a transmitting station using a first selected antenna and received at a receiving station using a second selected antenna which is selected as the antenna giving the best received signal quality, determined during the training signal period. Following transmission of the first packet, a control signal (ACKCNTL) is generated in both the transmitting station and the receiving station to condition these stations for the transmission from the receiving station of a response packet via the same antenna pair used for the information packet transmission. Thus, the response packet need have only a relatively short training signal portion.

Abstract: An arrangement for duplex transmission in a radio or similar device with a transmitter and receiver comprises a transmitter filter, receiver filter and preferably a transmitter/receiver device. The receiver filter may be a surface acoustic wave filter, and the transmitter filter and receiver filter are connected via a circulator. The arrangement also comprises a power detecting device for detecting the power into the receiver filter, and the power detecting device provides a feed-back signal to an arrangement for controlling the power out from a power amplifier arranged in front of the transmitter filter.

Abstract: An antenna suitable for a radio telephone which is primarily comprised of a duplexer, a transmitter, and a receiver. The antenna is fabricated as a cover for sealing a box-like duplexer. At the same time, the cover is set up by a microstrip antenna which is comprised of a dielectric substrate and conductive pattern layers formed on the top and bottom surfaces of the dielectric substrate.

Abstract: A radio transceiver is disclosed in which an antenna is connected to a transmitter or a receiver through a duplexer. A controller is provided to control the switching operation of the duplexer so that when an output of the receiver exceeds a predetermined maximum threshold level of the receiver, the antenna is connected to the transmitter through the duplexer while a leakage received power of the duplexer is applied to the input of the receiver.

Abstract: A method and apparatus system for cancelling a leak-through signal component generated by an interfering transmitter from a received/leak-through signal comprising a multiplier for multiplying the received/leak-through signal by a reference signal provided from the interfering transmitter. The system further includes an integrator for integrating the output of the multiplier to generate an estimate of the gain and phase of the leak-through signal component. A gain and phase adjustor, responsive to the generated gain and phase estimates, is also included for adjusting the gain and phase of the reference signal to generate a cancellation signal that is a substantially gain and phase matched estimate of the leak-through signal. The generated cancellation signal is then subtracted from the received/leak-through signal to substantially cancel the leak-through signal component.

Abstract: An antenna switching apparatus for selectively connecting an antenna to either a transmitter for transmitting a transmitting signal having a transmitting frequency, or a receiver for receiving a receiving signal having a receiving frequency, which is different from the transmitting frequency, includes an antenna terminal electrically connected to the antenna; a transmitting terminal electrically connected to the transmitter, and a receiving terminal electrically connected to the receiver. A receiving filter for passing a receiving signal therethrough is electrically connected between the antenna terminal and the receiving terminal. An impedance adjusting element is electrically connected to an input end of the receiving filter, and has an element value such that an impedance when seen from the antenna terminal looking toward the receiving filter becomes substantially infinity at the transmitting frequency.

Abstract: A multi-filter device comprising a ceramic block (10) having at least two filters A and B. Both filters A and B include a notch (11 and 13, respectively) formed on one side of the ceramic block (10), such that these notches are flanked by ceramic block material extensions (32). So configured, coarse tuning of the ceramic block (10) can be accomplished through use of existing double-sided lap techniques, yet constant parameter alteration for both filters will be maintained during the milling process.

Abstract: A triaxial transmission line provides for the transmission of two independent signals from a transmitter to an antenna utilizing the middle conductor as a portion of the coaxial line for both signals. One signal utilizes the inner and middle conductor and the second signal the outer and middle conductor. The outer conductor at both ends of the triaxial transmission is line is shorted to the middle conductor.

Abstract: Ceramic block filters can be constructed to have non-symmetrical, i.e. unequal, input and output impedances. These filters can be used to eliminate impedance matching networks in radio communications devices. These impedance matching networks (22, 14) are precluded when the input and/or output of a ceramic block filter (100) is controlled by appropriate selection of the physical parameters of the block to achieve a direct impedance match between an adjacent circuit element and subsequent signal processing stages in the device.

Abstract: An antenna coupler is inserted between an antenna and communication systems operating in two different frequency bands. A matching circuit allows signals in either of these frequency bands to be transmitted only between the antenna and a sorter corresponding to the frequency band which serves to sort signals in the frequency band into a reception band and a transmission band. Reception and transmission filters corresponding to the two frequency bands are provided for limiting reception signals received from the antenna and transmission signals from the communication systems within a reception band or a transmission band in the corresponding frequency band.

Abstract: A radio transceiver having improved impedance matching characteristics between a rod-like antenna and transmitting and receiving portions. An impedance matching circuit is provided between the antenna and a duplexer to impedance-match therebetween at a frequency within a desired signal frequency band. A transmitting signal and a receiving signal may have substantially different frequencies in which case the impedance matching circuit operates advantageously in a range between these signals, respectively. The impedance matching circuit includes a first inductor inserted between the antenna and the duplexer, a first capacitor inserted between the antenna and ground potential, and a parallel resonance circuit composed of a parallel circuit of a second capacitor and a second inductor inserted between the duplexer and ground potential.

Abstract: A downlink portion consists of a multiplexer for combining several signals. The combined signal is converted to an optical signal by a laser and transmitted over an optical line to a splitter. The split signals are each transmitted to a detector which converts the optical signals back into an electrical signal. The electrical signal is then filtered to provide the desired signal from the combined signal. The desired signal is then transmitted. The uplink portion consists of a plurality of receivers which receive signals from remote units. The received signals are multiplexed and converted to optical signals in a laser. The optical signals are transmitted over optical lines to a combiner which provides a single combined optical signal. The combined optical signal is then transmitted over optical lines to a detector which converts the optical signals to an electrical signal. The electrical signal is then demultiplexed into its constituent portions.

Abstract: A single chip receiver/transmitter section (202) includes an antenna switch (208), a low noise amplifier (210), a power amplifier (212) and a first (214) and second (216) mixers. The antenna switch (206)includes an antenna terminal (256) which is coupled to an off-chip band pass filter (206) which provides all of the selectivity for radio (200). Also described is a transmitter/receiver structure (300) which incorporates a transmission line filter such as band pass filter (206) formed by substrates (304) and (306) and includes the single chip transmitter/receiver section (202) imbedded inside of the structure (300).

Abstract: The invention relates to an apparatus which is desiged for underground use in order to facilitate a two-way communication. The apparatus is operated within the frequency band 0.1-2 MHz, in order to make the electromagnetic waves propagate advantageously by utilizing the metal structures installed in the underground facilities and the bedrock itself. According to the invention, the transmitter/receiver unit is provided with an analog to digital converter (5) and respectively a digital to analog converter (20) in order to transmit the intermediate signal coded in digital form in between the two units of the apparatus.

Abstract: A triaxial transmission line provides for the transmission of two independent signals from a transmitter to an antenna utilizing the middle conductor as a portion of the coaxial line for both signals. One signal utilizes the inner and middle conductor and the second signal the outer and middle conductor. The outer conductor at both ends of the triaxial transmission is line is shorted to the middle conductor.