Abstract: Switchable path length coupler/dividers. Coupler/divider operation over multiple frequency bands is provided by using switchable path lengths. In one implementation, a Wilkinson-style device with switches to select different path lengths and therefore operating frequencies. In a rat-race style device, switches select races of different lengths, and therefore operating frequencies.

Abstract: The present invention relates to a summing network comprising: a summing point (P) having interfaces for coupling summing network branches to the summing point, and an interface for coupling the summing point (P) to an antenna (ANT), and channel units (TX1 to TX3) arranged in the branches, and channel unit-specific band-pass filters (1 to 3), whose pass frequencies correspond to the frequency or frequencies of the corresponding channel unit. To facilitate tuning the summing network, a compensation element (7) is coupled to the summing network between the summing point (P) and the antenna (ANT), the load effect of said compensation element corresponding substantially to the load caused to the summing point (P) by the branches coupled to the summing point.

Abstract: A surface acoustic wave duplexer includes a branching section having a plurality of surface acoustic wave filters provided on a first electrode pattern on the front surface of a multi-layer substrate. An antenna terminal, a transmission terminal, and a receiving terminal are provided on peripheral portions of a fourth electrode pattern on the rear surface of the multi-layer substrate, and are connected to the branching section. A matching stripline disposed on a third electrode pattern in an intermediate layer of the multi-layer substrate, and connected to the antenna terminal is arranged such that it is grounded to at least one side other than the side opposite the side where the antenna terminal is located.

Abstract: Disclosed is an apparatus for commonly using an antenna for a call signal and a television (TV) broadcasting signal in a radio communication terminal including an antenna, a phone duplexer, a TV tuner, an LC parallel circuit, connected between the antenna and the phone duplexer, for forming an LC resonance circuit for a call signal frequency band, an LC series circuit connected to a connected point of the LC parallel circuit and the antenna and to a DC power supply terminal, a stub for impedance matching one terminal of which is connected between a capacitor and an inductor of the LC series circuit and the other terminal of which is connected to the TV tuner, and a path providing section for providing a path between a connected point of the stub and the TV tuner and a ground terminal in accordance with a switching control signal provided according to a TV or call operating mode.

Abstract: A multilayer band separator with a grounding parasitic capacitor. The separator includes a quasi-highpass filter, a semi-lumped lowpass filter and a phase shifter. The quasi-highpass filter includes a third capacitor connected to an input signal, a fourth capacitor with one end connected to the third capacitor and the other end connected to ground, an inductive element with one end connected to ground and the other end connected to the connection point of the third and fourth capacitors, and a second capacitor with one end connected to the connection point of the third capacitor, the fourth capacitor and the inductive element and the other end connected to a second output to pass a high-frequency output signal. The phase shifter is a transmission line element connected to the input signal.

Abstract: A system and a method for providing a global positioning system (GPS) enabled antenna system are provided. The GPS enabled antenna may be used, for example, on a wireless communications device such as a wireless handset. The wireless communications device may include a switching module that can selectively switch communications signals between the antenna and one of a plurality of communications band circuits. A respective impedance matching circuit may be provided between the switching module and particular communications band circuitry to match or to tune the antenna to the particular communications band circuitry.

Abstract: A system and method effectively combines communications of the base stations of multiple wireless systems on the same antenna structure. In one implementation, a wireless system combiner serves as an interface between base stations of first and second wireless systems (“first base station” and “second base station”) and a shared antenna to substantially eliminate spurious noise from the first base station at frequencies allocated to the second base station and prevent transmit power from the first base station from feeding into the reception circuitry of the second base station in a shared antenna configuration. The combiner includes a first combiner filter between a duplexer of the first base station and a common connection point and a second combiner filter between a duplexer of the second base station and the common connection point.

Abstract: A dual band transmitter (1) including: a lower band power amplifier (2) and a higher band power amplifier (3), a lower band transmit path (4) between the output of the lower band power amplifier (2) and a combining means (8); and a higher band transmit path (5); between the output of the higher band power amplifier (3) and the combining means (8). A surface mounted device includes a stub (6) having a first (61) and a second (62) end, the first end of the stub (6) being connected to the higher band transmit path (5) and the second end of the stub (6) being coupled to a switch. The second (62) end of the stub (6) is substantially closed or opened, in dependence upon the state of the switch, so that, in use, spurious harmonics are prevented from being generated in, and transmitted from, the transmitter (1).

Abstract: This invention relates broadly to rf coupling circuits enabling any platform-mounted antenna system and its associated standard broadcast-communications radio receiver, to also be used in conjunction with a navigational receiver. An exemplary embodiment of the invention is an antenna coupler for coupling a broadcast communications antenna with a broadcast communications receiver and a navigation receiver. The coupler includes independent rf paths for coupling the broadcast communications antenna to the broadcast communications receiver and to the navigation receiver.

Abstract: A signal divider/combiner (11) and method combines first and second frequency signals received by microstrip patch antennas (58, 48). A first transmission line stub (28) blocks the second frequency signals on the first signal receiving path, and a second transmission line stub (20) blocks the first frequency signals on the second signal receiving path providing increased signal levels at a receiver input (10). In one embodiment, the transmission line stubs are open-circuit stubs and are positioned a quarter-wavelength from a combining junction (12) formed from stripline transmission lines (14, 32, 50). The transmission line stubs (28, 20) also reduce radiation of the first frequency signal by the second antenna as well as radiation of the second frequency signal by the first antenna. In one embodiment, the first and second frequency signals are the L1 and L2 signals provided by the Global Positioning System.

Abstract: A multiplexer circuit adapted to receive standard cellular telephone signals and PCS signals without user intervention comprises two filter circuits. The first filter circuit presents a high impedance to signals outside the standard cellular frequency range from one antenna and the second circuit presents a high impedance to signals outside the higher PCS frequency range from a second antenna. A cell phone adapted to receive both frequency ranges will automatically detect the appropriate signal.

Abstract: A cable television tap (500) for receiving a forward signal including an information signal and a power signal. The tap (500) includes a diplex filter (520) for receiving the forward signal and for separating the information signal from the power signal at outputs of the diplex filter (520) and a plurality of subscriber ports (535) coupled to an output of the diplex filter (520) for receiving the information signal such that the information signal can be accessed at each of the plurality of subscriber ports (535). The tap (500) also includes a removable port device (555) coupled to the other output of the diplex filter (520) for receiving the power signal, and the port device (555) has a connector (550) so that the power signal can be accessed. According to the present invention, when the port device (555) is coupled to the tap (500), the information signal can only be accessed at the subscriber ports (535), and the power signal can only be accessed at the connector (550) of the port device (555).

Abstract: To achieve an improved matching of a power amplifier to transmission line impedances of different transmission branches in a dual band mobile phone there is proposed a new power amplifier output circuit for such a dual band mobile phone. This power amplifier output circuit comprises a transmission branch change over unit being connected to an output terminal of the power amplifier. Further, there is provided a second impedance matching means in at least one transmission branch and the transmission branch change over unit comprises at least two switching elements between the first impedance matching unit and the second impedance matching unit. Therefore, the disturbing influence of parasitic elements in the switching elements may be reduced significantly.

Abstract: The present invention provides a reconfigurable diplexer which is well suited for use with mulitple element antenna arrays. The diplexer includes a common, slot-line transmission line adapted to carry electromagnetic signals; a pair a separate slot-line transmission lines coupled to the common transmission line; each separate slot-line transmission line having an individual filter coupled thereto, wherein each filter is adapted to selectively give its respective separate slot-line transmission line a characteristic impedance dependent upon predetermined frequencies of the electromagnetic signals; and a separate slot-line balun associated with each separate slot-line transmission line and adapted for coupling signals to and/or from its respective separate slot-line transmission line. The diplexer may be configured to operate in several different bands such as the INTELSAT frequencies (7.2-8.4 GHz) or DSCS frequencies (11.7-14.5 GHz).

Abstract: An AM/FM/WB/CB/cellular telephone antenna includes a first frequency self-resonant circuit at a position above the lower end of the antenna such that the electrical length of the lower section of the antenna is equivalent to one-quarter wavelength for a frequency in the FM frequency range and a second frequency self-resonant circuit disposed below the first frequency self-resonant circuit. The first self-resonant circuit presents a high impedance in the FM frequency band and the second self-resonant circuit presents a high impedance in the cellular frequency range. The entire length of the antenna is equivalent to one-quarter wavelength in a frequency in the CB frequency band. The antenna wire is wound around a fiberglass core, and the FM self-resonant circuit is formed by a tightly wound, coiled section of the wire together with a thin-walled brass tube extending over the core in the area of the tightly wound section.

Abstract: A dual-band multilayer bandpass filter having a first filter unit (18) for filtering a first signal having a first frequency and a second filter unit (19) for filtering a second signal having a second frequency. First and second filter units are arranged in stacked ceramic layers. A first blocking element (20a, 20b; 25a, 25b; 25a', 25b'; 46a, 46b) is coupled to the first filter unit (18) for blocking the second signal from being applied to the first filter unit (18). A second blocking element (21a, 21b; 26a, 26b; 25c, 25d; 27a, 27b) is coupled to the second filter unit (19) for blocking the first signal from being applied to the second filter unit (19).

Abstract: An apparatus and a method for simultaneously transporting telephone signals and broadband signals on a single coaxial cable. The ring line and tip line of the telephone signals are dc coupled onto the inner and outer conductors of the coaxial cable, while the information wire and reference ground of the broadband signal are ac coupled onto the inner and outer conductors of the coaxial cable respectively. Low pass filters at each end of the coaxial cable pass the telephone signal in and out of telephone jacks while blocking the broadband signals. High pass filters at each end of the coaxial cable allow the broadband signals to pass in and out of coaxial connectors while blocking the telephone signals. The coaxial cable is isolated from earth ground to prevent shorting of the telephone electrical power to earth ground. A ground block may be added to connect the reference ground of the incoming broadband signal to earth ground.

Abstract: A test equipment interface circuit capable of acting as an interface between a wireless transceiver and a piece of test equipment for both high frequency band signals and low frequency band signals without the use of active or mechanical switches.

Abstract: A user terminal in the form of a handset 1 is disclosed wherein a common antenna 3 is operative to provide transmission and reception on a plurality of selectable services at different frequencies, the antenna being resonant and matched for at least one of the services, and non-resonant and unmatched for other services. The user terminal handset 1 employs a common antenna 3 directly for that service or those services for which the antenna 3 is matched and resonant. The user terminal handset 1 employs the common antenna 3 unmatched and non-resonant for those services whereon unmatched non-resonant antenna use is acceptable. The user terminal handset 1 comprises means, for approximately or precisely adjusting the match to the common antenna 3 for other services.

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 impedance matching circuit for a multi-band power amplifier has an input port for receiving RF signals from an amplifier, a first path for communicating RF signals in a first frequency band to a first output port, and at least one second path for communicating RF signals in a second frequency band to a second output port. The first path includes impedance matching circuitry for matching the impedance of the first output port and the input port in the first frequency band, and the second path includes impedance matching circuitry for matching the impedance of the second output port and the input port in the second frequency band. The first path contains circuitry which blocks RF signals in the second frequency band, and the second path contains circuitry which blocks RF signals in the first frequency band. A multiband power amplifier includes a multi-band amplifier coupled with an impedance matching circuit for a multiband power amplifier.

Abstract: A bandstop filter module (200) with a shunt zero is provided. The module (200) contains a circuit substrate (202) with input and output pads and transmission lines (208). The module (200) also contains at least one dielectric monolithic block (210) mounted to the circuit substrate (202) having a plurality of metallized through holes defining resonators (224) and guard holes (226). All surfaces of the dielectric monolithic block (210) are substantially covered with a conductive material with the exception that the top surface (212) is selectively metallized providing an unshorted metallization pattern (228) relative to a ground plane in proximity to the guard holes (226). The guard holes (226) and the unshorted metallization pattern (228) provide a shunt zero in a frequency response curve of the module (200). The module also contains means for coupling each of the resonators (224) with the transmission lines (208) on the circuit substrate (202).

Abstract: A cordless communication apparatus which improves the performance of data transmission and reception by preventing the bandpass loss and the deterioration of frequency characteristics, which are caused during coupling a transmission output unit and reception input unit for using a single antenna. The apparatus minimizes power consumption, which is produced in using a .lambda./4 transmission path, thereby improving communication sensitivity. Also, since an expensive duplexer filter is not used, the manufacturing cost is reduced, thereby improving the price competitiveness of products.

Abstract: A high performance bandpass filter is produced by adding one or more "simultaneous couplings" to a conventional resonant cavity filter. A "simultaneous coupling" is created when a filter's input or output signal, normally coupled to a filter's first or last cavity respectively, is coupled to one or more other cavities. Each simultaneous coupling causes a finite-frequency insertion loss pole to be created, which produces a quasi-elliptic frequency response on its side of the passband. These poles may be placed on the left and/or right sides of the passband, so that both symmetric and asymmetric quasi-elliptic frequency responses are realizable. A diplexer constructed from two such bandpass filters has the extremely sharp selectivity provided by two asymmetric bandpass filters, thus providing a high degree of receive/transmit isolation.

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 system (10) for combining a plurality of transmission channels within a multiple channel communication system includes a master computer (20) that controls the transmission frequency and schedule of a plurality of channel transmitters (18). Each channel transmitter (18) is electrically connected to a channel transmitter combiner filter (12). Each channel transmitter combiner filter (12) is fixedly tuned to a unique bandwidth window along the electromagnetic spectrum, and two sets (24), (26) of channel transmitter combiner filters are formed of the channel transmitter combiner filters (12) whose unique bandwidth windows are adequately spaced for electrical isolation along the electromagnetic spectrum. Each set (24), (26) of channel transmitter combiner filters is electrically connected to a common antenna (28) by means of a three decibel (3 dB) coupler (22).

Abstract: A multilayer duplexer package is provided, which includes: two surface-acoustic-wave filter chips having different center pass band frequencies; and at least two phase matching circuits for matching the phase of one filter chip to that of the other filter chip, said phase matching circuits respectively comprising strip lines stacked one above another, and said strip lines each having a characteristic impedance higher than the characteristic impedance of an external circuit to be connected to the duplexer package.

Abstract: A system and method for decreasing the amount of bandwidth required to transmit a high bandwidth signal over electrically conducting transmission lines, wherein the transmission lines are arranged in a symmetrical configuration so that their propagation characteristics permit frequency independent modes of propagation of a plurality of signals to be transmitted thereon. This permits decomposing a high bandwidth signal into lower bandwidth signals, and then encoding these lower bandwidth signals in association with the frequency independent modes of propagation, driving the individual electrically conducting transmission lines with these encoded signals, and then decoding and recombining the signals at the receiving end to recapture the high bandwidth signal.

Abstract: An object of the present invention is to improve the characteristics of the conventional antenna duplexer and to provide an antenna duplexer contributing to higher performance and smaller size of a mobile communication apparatus. The antenna duplexer has a filter for wave receiving and a filter for wave transmission, and respective one ends of both the filters are connected to an antenna shared terminal through a matching circuit constituted by transmission lines. The characteristic impedance of at least one of a transmission line for connecting the antenna shared terminal and the filter for wave receiving to each other and a transmission line for connecting the antenna shared terminal and the filter for wave transmission to each other is set to a value other than the standard characteristic impedance of a receiver circuit and a transmitter circuit connected to the antenna duplexer.

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: This invention provides for separating undesired signals from spectra of desired signals in a communication system. Specifically, a communication system for transmitting and receiving spectra of signals having undesired signals and desired signals comprising: a transceiver system; a TEE-junction coupled to the transceiver system and having first and second ports, the undesired and desired signals being separated at the TEE-junction; an Off-line signal interference reduction device coupled to the first port, the Off-line signal interference reduction device receiving the undesired signals from the first port; and an In-line signal interference reduction device coupled to the second port and an antenna system.

Abstract: Two unequal impedance input port RF power combiner is used alone or as a component of a three equal input impedance input port RF power combiner with isolation between all ports. The combiner has a band pass of at least two octaves and the capacity to handle at least 5 kw. The combiner may be used in a transmission system and methods of isolation of the input ports by the resistive shunting of selected transformer windings are disclosed.

Abstract: A branching filter in which an input/output port, a first dielectric filter for use in transmission and a second dielectric filter for use in reception are coupled with each other through a branching filter circuit. The branching filter circuit includes a first line provided between the input/output port and an input port of the second dielectric filter, a second line provided between the input/output port and an output port of the first dielectric filter, and a third line provided between the input/output port and the ground. In the filter, conductor lines for use in connection between ports are used for the first and second lines.

Abstract: An antenna sharing device having a transmission filter connectable between a branch node of an antenna and a transmitter and a reception filter connectable between the branch node and a receiver. At least one of the transmission filter and the reception filter includes: a first parallel resonance circuit having a capacitor and a coil connected in parallel; a second parallel resonance circuit magnetically coupled to the first parallel resonance circuit; and a capacitor serially connected to the first parallel resonance circuit. One of the first and second parallel resonance circuits has a first resonance frequency, the other of the first and second parallel resonance circuits has one of the first resonance frequency and a second resonance frequency, and a combination of the first and second parallel resonance circuits and the capacitor forms an equivalent circuit providing a small insertion impedance at a third resonance frequency.

Abstract: A new class of multiplexing filter structure has both the properties of channelized filtering and channelized linear frequency discrimination. The channelized filter-discriminator is intended for use as part of a microwave receiving system possessing a high probability of intercept for incoming signals. The selective properties of the band pass filters provide an interference-reduction capability while the discriminator property provides for instantaneous frequency measurement. The design procedure for achieving a very high degree of discriminator linearity in association with a reasonable selectivity comparable to a maximally flat filter uses theoretical design data provided in a normalized table generated by computer optimization. A hardware realization of a 64 channel multiplexer-discriminator is described and measured data is presented that agrees very closely with the theoretical predictions.

Abstract: A multiple coupler which comprises a low-pass path (VPB) and a high-pass path (VPH) and frequency separation elements comprising a capacitive element C and an inductive element L, whose impedances Z.sub.c and Z.sub.l, respectively, satisfy the relation Z.sub.c Z.sub.l =Z.sub.o.sup.2. The low-pass path comprises a phase inverter INV to enable recombination of the signals without any distortion.

Abstract: TV-RF input circuit provided with an RF coupling device via which an aerial input is coupled to first, second and third parallel tunable RF resonant circuits (11, 21, 31) for a parallel selection of a desired frequency in first, second and third TV frequency bands (50-160 MHz; 160-470 MHz; 470-860 MHz) substantially succeeding one another in frequency, the RF coupling device having a high-pass .pi.-section (C, L2, L3) for suppressing frequencies below the first TV frequency band and being provided with a capacitive series branch and first and second inductive shunt branches, the .pi.-section (C, L2, L3) being coupled via a first series inductance (L1) to the first RF resonant circuit (11).

Abstract: A network is provided which is selectively configurable as a high pass and low pass filter. A pair of sets of field effect transistors FETS is provided, each set comprising three FETS connected in a T-configuration. A pair of the FETS in each set have a drain electrode of one FET coupled to the source electrode of the other FET to provide a series element of the T-configured set. The third FET has drain and source electrodes coupled between the common connection of the pair of FETS and ground to form a shunt element of the T-configured set. The gate electrodes of the series elements of a first one of the sets of FETS and the shunt element of the other set of the FETS are each fed a common control voltage signal. A first one of the sets of FETS is capacitively coupled between the input and output terminals of the network, and the second one of the set of FETS is inductively coupled between the input and output terminals of the network.

Abstract: Input and output equipment are provided for connecting first and second wideband signal transmission mediums through link equivalent to a balanced transmission line. The line can be made up of crosspoint cells includes in a wideband switching matrix, or can be a line distributed to intermediate equipments in a videocommuncation network. The input equipment includes means for separating high and low frequency signals included in the received wideband signals, means for transmitting the high frequency signals in differential mode, and means for transmitting the low frequency signals in High-Input Low-Output (HILO) mode. The output equipment includes means for taking the high and low frequency signals separately and means for summing the high and low frequency signals into wideband signals to be transmitted in the second medium.

Abstract: A dual band, phased array antenna especially adaptable for tactical radar capable of performing search, track and identification in a hostile jamming environment. The dual band array antenna is essentially two antennas sharing a common antenna aperture. The two antennas possess separate feed system and beam steering control. Thus, the beams for each frequency band can be steered independently and simultaneously. This design utilizes an ultra-wide band radiating element which can operate over approximately an octave bandwidth encompassing two adjacent microwave bands. In particular, the dual band signals can be received efficiently by the radiating element. A dual band coaxial-to-waveguide transition can be used to carry the signals to a diplexer. The dual band signals are separated at the diplexer and can be processed in separate feed networks.

Abstract: A circuit for receiving voice and data signals on a balanced line, the data signal being an amplitude modulated form of a carrier signal having a frequency at least twice as high as the highest frequency in the voice band. The circuit matches the input impedance thereof to a first nominal balanced line impedance with respect to voice signals and a second nominal balanced line impedance with respect to data signals, applies the data signals to an unbalanced data output terminal, and applies the voice signals to a terminal connected to a bidirectional unbalanced input/output lead of a PABX.

Abstract: A duplexer includes an integral interdigital transmitter filter and parallel interdigital receiver filter in a common housing. A three-quarter wavelength antenna transformer section couples rf energy from the transmitter filter to an antenna and also couples rf energy from the antenna to the receiver filter and to an antenna cable connector. The receiver filter selectivity is improved by providing a notch resonator between a receiver transformer section and the housing, and the transmitter filter selectivity is improved by providing a notch resonator between a transmitter resonator and the housing.

Abstract: A television receiver of the type capable of displaying standard VHF and UHF televison signals is provided with a single coaxial antenna input terminal. A passive input circuit within the receiver includes two filter sections for separating the VHF and UHF components of a combined VHF-UHF signal applied to the input terminal for application to separate VHF and UHF tuning sections of the receiver. The first filter section, which is located within the UHF tuning section, includes a UHF tuning line for coupling the UHF component to the UHF tuning section. The second filter section, which is located in the VHF filter section, and incorporates elements of the first filter section, enhances the response of the receiver over transition frequencies between the VHF and UHF bands.

Abstract: Signals to be discriminated are supplied through a controllable attenuator and power splitter to first and second discriminators with response slopes which are equal and of opposite sign. The outputs of the discriminators are summed and a reference signal is subtracted from the sum to produce a control signal which adjusts the input attenuator to maintain the amplitude of the input signal constant. The outputs of the discriminators are also subtracted to provide an output signal which is a linear function of frequency and independent of input amplitude.

Abstract: A signal splitter-balun assembly for coupling a UHF antenna and a VHF antenna to a single input terminal of a television receiver is disclosed. RF isolation is provided by means of appropriate filtering, 60 Hz isolation is provided by means by a pair of capristors, and the required impedance transformation is provided by means of a conventional balun transformer in a low cost unit utilizing a minimum number of components.

Abstract: A circuit for coupling a citizens band transceiver and a broadcast band receiver to a standard automobile antenna. The circuit is comprised of an impedance transforming network connected in series with the standard automobile antenna and a parallel-tuned circuit in series with the broadcast band receiver. The series-tuned network is comprised of a split capacitance for stepping the impedance down from the citizens band transceiver to the lower impedance of a standard automobile antenna. The series-tuned circuit also includes a tuning coil for matching the output of the network to the particular automobile antenna. In series between the automobile antenna and the broadcast band receiver is a parallel-tuned circuit comprised of a capacitor and a tuning coil. To prevent multiplication and excessive voltages in the event the broadcast band receiver should become disconnected, a limiting resistor connects the parallel-tuned circuit to ground.

Abstract: Data signals are transmitted from a transmission unit (12) through a hybrid coil (16) and transmission line (18) to a remote transceiver. Data signals of a different frequency are received from the remote transceiver through the transmission line (18) and hybrid coil (16) in a full duplex mode and passed to a reception unit (26). A ratio of the signal levels of the received data signals passed through the hybrid coil (16) in a desired manner to transmitted data signals which leak through the hybrid coil (16) in an undesired manner is sensed at a reception signal output of the hybrid coil (16). The resistance of a variable resistance pad (17) provided in the transmission line (18) is varied in accordance with the sensed ratio so as to adjust the ratio to a predetermined optimum value. The sensed ratio is a predetermined function of the impedance of the transmission line (18) as viewed from the hybrid coil (16).