Showing papers on "RF power amplifier published in 1974"

Automatic Load Contour Mapping for Microwave Power Transistors

Abstract: A technique for large signal characterization of microwave power transistors is described. A computer controlled apparatus is used to map contours of constant output power and efficiency, on a Smith Chart, for dynamic matching of both input and output circuits.

Multiple band scanning radio

Abstract: To scan channels in a plurality of bands using a single first mixer, an FET transistor in an adaptive first mixer of the scanning radio, in response to a signal from a counter in the scanning local oscillator representing the frequency band of the channel being scanned, has: (1) its gate electrode connected to the output of a selected RF amplifier of a plurality of RF amplifiers for different bands; and (2) its source electrode electrically connected to receive local oscillations through a selected one of a plurality of different impedance networks. These connections enable the adaptive first mixer to maintain sufficiently high conversion gain when receiving signals on channels in any one of a plurality of different frequency bands.

Variable gain amplifier controlled by ambient noise level

Abstract: An audio amplifier system is provided comprising a variable gain amplifier adapted to receive an input signal, means for detecting periods when the input signal falls below a predetermined level, and sound transducer means arranged to provide a signal proportional to the sound level in the area or part thereof covered by the system for controlling the gain of the amplifier An inhibitor is provided which is arranged to be controlled by the detecting means so as to prevent any change of the gain of the variable gain amplifier except during periods when the input signal falls below the said predetermined level

Amplifier circuit having power supply voltage responsive to amplitude of input signal

Abstract: There is provided an amplifier circuit wherein the changing of power supply voltages is effected in accordance with the amplitude of an input signal. The amplifier circuit comprises an amplifying transistor having its base adapted to receive an input signal and its emitter connected to a load, a switching transistor having its base and emitter connected respectively to the base and collector of the amplifying transistor, a first power source for supplying power to the collector of the switching transistor, and a second power source for generating a voltage lower than the output voltage of the first power source and supplying power to the collector of the amplifying transistor.

Low power consumption stereo transmitter and receiver system

Abstract: A low power consumption, compact portable stereo radio transmitter and a receiver therefor, the transmitter having two audio processing channels each for receiving inputs from two stereo pickup stations and including amplifier circuits with selector switches providing a mode of even harmonic generation, a mode of odd harmonic generation, and a mode of undistorted amplification, a 38 KHz oscillator, flip flop coupled to the oscillator to provide a 19 KHz pilot signal, a difference amplifier and a balanced mixer to produce a double-sideband suppressed carrier signal centered on 38 KHz, and an amplifier for combining the balanced mixer output, the pilot signal and the two channel output and modulating a carrier signal. The receiver includes amplifier, detector, and decoder circuitry to receive the radio signals from the transmitter and produce stereo audio signals for driving a standard stereo amplifier.

Tunable microwave notch filter

Abstract: A recursive microwave notch filter wherein each section is comprised of a pair of power dividers e.g. 3-db couplers joined by a short and a long microwave transmission line. Tuning of the frequency rejection notch is achieved by inserting an electrically controlled phase shifter having 360* of adjustment in the short transmission line. Two identical cascaded sections of the subject notch filter are required for coupling to the input of a saturated RF power amplifier, such as the output amplifier of an amplifier chain utilized in present day radar transmitters, in order to obtain the desired frequency rejection notch, due to the gain compression characteristic present in an amplifier when driven into its saturation region.

Reliable earth terminal for satellite communications

Abstract: A reliable earth terminal for satellite communications systems capable of unattended operation for extended periods of time is disclosed. The terminal includes an antenna with a single fixed reflector which can provide multiple beams, each of which can be positioned by small feed motion. The transmitter is of a modular construction, using a relatively low power traveling wave tube power amplifier for each increment in the operating band. The transmitting chains are designed to carry voice, data, or television signals to a satellite and include a modulator, IF amplifier, band-limiting filter, frequency converter, and power amplifier. Each amplifier is capable of operating over the full operating band; however, operation of each amplifier is limited to an assigned increment through the use of band-limiting filters. A single, redundant high power amplifier is provided and may be remotely switched into any one of the transmitting chains in the event of a failure. Amplifier outputs are connected to the antenna through a directional filter multiplexer. The receiver includes a low noise preamplifier featuring modular, "fail-soft" design. The receiving chains following the low noise preamplifier are channelized into band increments corresponding to those of the transmitting chains with separate converter and demodulator modules for each carrier. All subsystems are broadband, and channel bandwidth is determined only by intermediate frequency band pass filters. Prime power is low voltage battery banks constantly recharged by a commercial power source. The terminal can be operated for a limited period of time solely on the battery bands during commercial outages. A back-up motor generator provides recharging power during extended periods of commercial outages. The terminal is monitored and controlled from a central control point. Since the terminal is both automatic and self-protecting, remote control is limited to parameter adjustments required for normal operation, such as antenna feed positioning, changes in transmitter power, and switching to the spare power amplifier or turning off any carrier.

Time domain laser reconnaissance technique

Abstract: Method and apparatus for producing imagery of an object having distinct vertical geometry characteristics located at a reference plane remote from a scanning laser. In particular, a laser beam is utilized to scan objects at the reference plane and the optical signal reflected therefrom, corresponding to the reflectivity of the objects and background, is detected. An electrical signal, corresponding to the detected reflectivity signal, is coupled to an RF amplifier, the output of the RF amplifier being applied to an amplitude demodulator. The output of the amplitude demodulator, corresponding to the reflectivity and vertical geometry characteristics of the object at the reference plane, is applied to a recording device to produce the aforementioned imagery.

Transistor series amplifier

Abstract: Bias for the n cascade connected output transistors of a conventional series amplifier is obtained by applying successive increments, each 1/n times the output voltage available across the series connected conduction paths of these transistors to the control electrodes of the successive transistors in the cascade, except for the one connected to the load terminal. Drive signal is applied to the control electrode of this transistor. In accordance with the present invention, the drive signal is supplied via n cascade connected input transistors biased in similar fashion to the cascade connected output transistors, to develop across its conduction path a voltage approximately equal to 1/n times the amplifier output voltage. This way of applying drive signal to the series amplifier facilitates its connection with another series amplifier in push-pull amplifier configurations.

Isolated output system for a class D switching-mode amplifier

Abstract: A Class D amplifier for the amplification of signals having unipolar or bi-polar direct current, or alternating current, content comprising positive and negative signal channels and including a transformer-coupled output circuit for each channel which includes a switching circuit which effects isolation of the nonoperating channel from the operating channel as a function of signal polarity.

Apparatus for reducing distortion in a repeatered transmission system

Abstract: The distortion generated due to the nonlinear characteristics of the power amplifier in a repeater network is substantially reduced by generating a compensating signal in a feedforward amplifier network. In the feedforward network an auxiliary amplifier having substantially the same gain and distortion characteristics as the main power amplifier generates a compensating signal having a linear component equal to the linear component of the output signal of the power amplifier and a distortion component equal in magnitude to the distortion component of the output signal of the power amplifier. The phase relationship between the linear and distortion components at the output of the auxiliary amplifier is, however, opposite to the phase relationship between the linear and distortion components of the power amplifier. Thus, when the compensating signal is combined with the output of the power amplifier, the distortion components are substantially canceled and the linear components are added. The substantially distortion-free output signal has greater power than was obtainable in prior art feedforward distortion reduction networks.

Power and modulation control system

Abstract: A system for controlling and maintaining the power output of a broadcast transmitter under varying line voltage conditions, including a pulse width modulator wherein a triangular wave acting as a reference input is compared to the audio input Power is controlled by varying the amplitude of the triangular wave relative to the audio input which additionally includes a DC bias thereby increasing or decreasing the comparator square wave output duty cycle which output is used to control the transmitter's RF power amplifier Three separate DC control inputs, respectively, for automatic power control, remote or local manual power control, and a slow start control are summed and fed to an operational DC amplifier which provides a composite DC output which is fed to a triangular waveform generator in order to control the amplitude of the triangular waveform generated thereby

RF Power transmission line

Abstract: Transmission line for RF power utilizing generally flat supply and return lines each comprising a plurality of flexible, insulated conductors connected together at their ends. The two lines are enclosed in a flexible sheath which holds the lines in close proximity to each other, and fields produced by the lines tend to cancel each other.

Accurate normalization for a monopulse radar

Abstract: The invention comprises a system for controlling and normalizing the gain of the difference I.f. I.F. to the gain of the sum I.F. amplifier in a monopulse radar. A pulsed, I.F., pilot signal is applied to both the sum and difference I.F. amplifiers at predetermined intervals chosen so that the pilot signal does not interfere with the echo return signal. The outputs from these I.F. amplifiers are gated at the predetermined intervals coinciding with the application of the I.F. pilot signal. These gated, sum-and difference-amplifier, pilot signals are envelopedetected and then applied to a differential amplifier. This differential amplifier generates a signal representative of the difference between the sum and difference amplifier pilot signals and applies this signal to the difference, I.F. amplifier to control its gain. The sum I.F. amplifier has a conventional A.G.C. system for gain control. The control signal generated by this conventional A.G.C. system is also applied to a circuit for controlling the signal level of the I.F. pilot signal so it is inversely proportional to the signal gain level of the sum I.F. amplifier. This controlled I.F. pilot signal is then applied to the sum and difference I.F. amplifiers (as stated above) via a hybrid network and directional couplers, at a time chosen so that it does not interfere with the predicted echo-return.

Modular CATV system

Abstract: A CATV system is described wherein distribution cables are provided with amplifying means spaced at uniform intervals therealong. The amplifiers are provided with an input tap and two output taps, the first of which provides the usual gain to provide an output level equal to the input level plus the attenuation suffered by the signal traversing the cable from the preceding amplifier. The second output is provided by each amplifier by tapping the output signal at the first output tap with a directional coupler and processing the signal through an equalizer and coupling the output of the equalizer through a second directional coupler to a second output terminal. The signal derived at the second output terminal is such that a second identical amplifier connected to it will produce in its first output the signal levels required in the feeder system, when the first amplifier is operated at the signal levels appropriate for the main trunk system. Typically, the second output terminal is at a level equal to the input level for that signal plus one-half of the attenuation suffered by that signal traversing the cable from the preceding amplifier; for this case, the signal at the second output is chosen at a level that would otherwise occur at one-half of the normal amplifier spacing along the cable. The output level available at the second output is also applied through a directional coupler to a 4-way splitter, the output of which is connected to four house taps also provided on each amplifier.

Protective system for stereo loudspeakers

Abstract: In an amplification system comprising an amplifier, a loudspeaker, normally open contacts connected in series between the amplifier and the speaker, and a power supply for the amplifier having relatively long buildup and decay times of its output voltage in response respectively to the connection and disconnection of the power supply to and from the a.c. line, means are provided responsive to the connection of the power supply to the a.c. line for delaying the closing of the normally open contacts until after the power supply voltage has built up to its full operating potential for eliminating the transient audio signals from the amplifier associated with power supply voltage buildup from being reproduced by the loudspeaker. Means are also provided for opening the contacts quickly after the power supply is disconnected from the a.c. line for eliminating the distorted audio signals from the amplifier associated with power supply decay from being reproduced by the loudspeaker. Additionally, if the amplifier is of the balanced type which exhibits a zero d.c. output potential during normal operation, means are provided for quickly opening the contacts upon the occurrence of a high d.c. amplifier output potential of either polarity for protecting the loudspeaker.

Battery powered scanning receiver with synchronous power cycling through electrically operable visual indicators

Abstract: A receiver is disclosed for signal-seeking operation on a plurality of channels. The receiver uses power cycling of the RF amplifier stage, mixers, local oscillators and intermediate frequency amplifiers which is in synchrony with the electronic stepping switch used to sequence among the channels. The power which is cycled to these portions of the receiver passes in series through light emitting diode channel indicators.

A phase-coherent, extended-frequency-range, high-power rf transmitter system for pulsed nuclear magnetic resonance

Abstract: A high‐power transmitter for pulsed nuclear magnetic resonance experiments in the frequency range 2–200 MHz is described. Frequencies below 40 MHz are provided by a multistage, 15 kW (peak rms power), variable‐tuned, rf amplifier; the power output can be increased to 100 kW by means of a single‐stage booster. Frequencies between 40 and 200 MHz are provided by a three‐stage 20 kW frequency multiplier which can be tuned to either triple or quintuple the output of the low‐frequency amplifier. Extension of the high‐power multiplication scheme to higher frequencies is discussed. Finally, a versatile spectrometer system is described which illustrates the practical utilization of the transmitter.

Superconducting microwave cavities and Josephson junctions

Abstract: The possibility of using very‐high‐Q superconducting microwave cavities to obtain a strong coupling between the electromagnetic field and a Josephson junction has prompted a study of such systems. Expressions have been obtained describing the dc I‐V characteristic of a junction biased so that the Josephson radiation frequency is near a resonance of the cavity in which it is located. The rf power coupled into an X‐band (10 GHz) TE011 mode cavity from a weakly coupled junction is approximately 3×10−13 I02 Q W, where I0 is the critical current of the junction and Q is the cavity Q. When the coupling between the junction and cavity is large enough, the I‐V characteristic becomes multiple valued and the power coupled to the cavity depends on the state of the system. The maximum power which can be coupled to the cavity is approximately 0.58I0Vdc, where Vdc is the voltage required to bias the junction to the resonant frequency of the cavity.

A Four Stage, 30 DB Gain, 100 MW Gunn Effect Amplifier in Ka-Band

Abstract: Design and performance of a four-stage, 30 dB gain Gunn effect amplifier are described. The frequency response at different input power levels in given, as well as gain variation versus temperature. Saturated output power is 250 mW.

A 6 GHz silicon bipolar power transistor

Abstract: The design features of an experimental 6 GHz power transistor are presented. The power performance of the transistor in class A - common emitter, and in class B - common base for a range of inputs, is shown. In class C - common base, the gain and efficiency at 4, 5 and 6 GHz are plotted. The contributing factors to this performance are discussed.

Low noise rf signal generator

Abstract: A signal generator for generating a high power low noise RF signal is disclosed. The generator includes a low noise crystal control oscillator for generating a relatively low power, low noise RF signal. The output signal of the oscillator is coupled to a high power RF amplifier which amplifies this signal to generate the low noise high power RF signal. The low frequency noise of the oscillator is reduced by a low frequency negative feedback loop in the oscillator circuit. Noise induced into the oscillator circuit by load changes in the power amplifier is reduced by designing the amplifier such that its input impedance is substantially constant for all phase angles of the RF signal.

Power Absorption in High Power Microwave Discharges

Abstract: Measurements on RF power absorption in microwave discharges at 2.45 GHz, at pressures from 1 to 30 Torr in N2 and from 1 to 500 Torr in Ar, are described. A linear slow-wave structure of the strapped-bar type was employed for coupling RF energy to the plasma. From measurements on the plasma volume and on the total power absorbed, the variation with gas pressure of the RF power density in the plasma was obtained. For an incident power of 1 kW, power densities as high as 2-3 W/cm3 over relatively large plasma volumes could be achieved. The experimental data were used to calculate the pressure dependence of the electron density in an argon plasma, for an incident power of 1 kW.

X-band RF power performance of GaAs FET's

Abstract: The design and development of high RF power GaAs FET's is the subject of this paper. A mature planar fabrication process developed for small signal FET's having: gate lengths ≃ 2µ is described. Very respectable Pf2X values at X-band have been achieved with these 300 µ gate width devices. One approach to higher power devices is simply to extend this established planar device technology to larger gate widths. We have fabricated FET structures with 1000 µ and 2000 µ gate widths and multiple source pads and their RF performance is presented here. A potential scheme for interconnecting the source pads to ground with minimum parasitlcs is discussed along with a novel FET device structure utilizing the fabrication techniques of the GaAs IMPATT technology.

Electrical musical instrument amplifier having improved tremolo circuit, improved reverberation control, and power reduction circuit for distortion mode operation

Abstract: An electrical musical instrument amplifier is disclosed in which a signal which has been provided by an instrument to a second one of two different preamplifiers for amplification therein is passed to one of the inputs of a summing amplifier together with the output of the first preamplifier, the output of the summing amplifier being coupled through a tube driven power amplifier to a loudspeaker system. The amplified signal from the second preamplifier is applied to a second input of the summing amplifier via a circuit arranged as a voltage divider and having a variable resistance provided by a field effect transistor driven by an oscillator. The modulation provided by the field effect transistor and associated oscillator can be adjusted to provide total phase reversal as well as amplitude modulation when combined with the signal at the output of the second preamplifier, to provide a tremolo or vibrato effect. Improved reverberation control is provided by a control common to the volume controls of both a delayed reverberation signal from the second preamplifier and the combined signal which results when the instrument signal from the second preamplifier is combined with the delayed reverberation signal. The power amplifier can be operated in a distortion mode to achieve desirable harmonics without overloading the voice coils in an attached speaker system through use of a power supply which applies reduced voltages to the power amplifier whenever the gain of the power amplifier is adjusted to a high setting while at the same time regulating the voltage applied to the first and second preamplifiers to keep such voltage constant.

Signal phase detector

Abstract: The signal phase detector according to this invention comprises a differential amplifier with a couple of transistors, a first transistor inserted between the emitters of the couple of transistors and a first point of reference potential, a second transistor inserted between the output terminal of one difference the transistors of the differential amplifier and a second point of reference potential, a third transistor connected to the second point of reference potential, and a fourth transistor connected in series with the third transistor and between the output terminal of the third transistor and the output terminal of the other of the transistors of the differential amplifier. A reference signal is applied to the base of the first transistor, while a signal to be compared is applied to the base of one of the transistors of the differential amplifier, so that an output signal corresponding to the phase differential between the two signals is obtained from the output terminal of the other of the transistors of the differential amplifier.

A new concept of ballasting mechanisms of microwave power transistors in class C operation

Abstract: Emitter ballasting in class C microwave power transistors is shown to cause a sacrifice of output power and collector efficiency. The use of base impedance balasting resulted in the development of an experimental 4 GHz microwave power transistor which is capable of providing 3 watts of output power with a 6.4 dB power gain and a 65% collector efficiency. The experimental data on the collector current dependence of the power gain, and the spatial temperature distribution of the device working in class C and class A operations are presented. General guidelines for designing class C microwave transistors for optimum performance are given.

High Efficiency Read Diode Amplifier

Abstract: Impedance characteristics of Read-profile IMPATT diodes are evaluated and amplifiers operating in the stable reflective mode have been designed based on the measured diode impedance. Power output of up to 4.5 Watts was obtained in a one stage single diode amplifier with a gain of 4.5 dB and an efficiency of 22 percent.

Class ab-dual push-pull amplifier

Abstract: A push-pull transistor amplifier wherein the transistors are biased in the Class A region but near collector saturation. An inductance is series coupled with the collector source to permit the amplifier to handle large peak-factor signals. A diode is connected in parallel with the collector-base junction of each transistor to prevent charge storage effects.