Abstract: A filter device includes a super-conducting type filters connected in series with each other and is accommodated in a vacuum chamber. Operating temperatures of the filters are controlled to different temperatures from the outside of the vacuum chamber independently of each other. Each filter varies its filtering characteristics, particularly its central frequency of pass-band, in correspondence with the operating temperature, while maintaining the same pass-band width. As the filters operated at the different operating temperatures provide different filtering characteristics, the combined or resulting filtering characteristics of the filtering device can be adjusted as desired even after the filtering device is installed at a mobile telecommunication base station.

Abstract: A grounded-base transistor amplifier including a pair of transistors which have the bases thereof grounded at a high frequency and the collectors thereof coupled to a signal output terminal, a high frequency transformer which includes a primary winding connected to a signal input terminal and a secondary winding equipped with a midpoint tap, both ends of the secondary winding being connected to the emitters of the transistors, and a constant-current circuit which is connected to the midpoint tap of the secondary winding and which produces a bias current flow through the transistors. Noise voltages generated by the constant-current circuit are supplied to the emitters of the transistors in the same phase via the secondary winding; therefore, no noise voltage appears at the signal output terminal.

Abstract: A balanced mixer is used as a switch. In digital mode, the balanced mixer receives a digital mode analog waveform and a local oscillator (L.O.). The balanced mixer mixes the waveform and the L.O. to provide a resultant output signal. In analog mode, the L.O. is modulated to contain the communication information. No analog signal is present on the port of the mixer which received the digital mode analog waveform in digital mode. The desired output of the mixer is the modulated L.O. In order to pass the L.O. through the mixer, a DC bias is applied to one of the waveform terminals of the mixer to unbalance it. A diode attenuator is added to the output of the mixer to provide scaling of the analog mode output.

Abstract: A high-frequency band amplifier system which is capable of containing the amount of ripple produced in the band passed by an SAW filter, and which is also capable of avoiding an increase in the noise factor. Such an amplifier system is constructed of a surface acoustic wave filter and a common-base connected transistor amplifier for amplifying the output from the surface acoustic wave filter.

Abstract: A transmitting/receiving unit capable of setting the level of power for transmitting an output frequency signal, which correctly correspond to the level of a received frequency signal, without dependency upon change in the environmental temperature, the transmitting/receiving unit including a signal transmitting portion; and a signal receiving portion so as to be capable of generating an output signal, the level of which depends upon the level of a received signal, wherein the signal transmitting portion includes first variable-gain amplifying means having an amplified gain which is varied by first AGC voltage, the signal receiving portion includes second variable-gain amplifying means having an amplified gain which is varied by second AGC voltage, wave-detection means for generating DC voltage which is in proportion to level of an output signal from the second variable-gain amplifying means, and temperature-dependent-type automatic gain control voltage generating means for converting the DC voltage into AGC

Abstract: A control circuit for a multi-stage power amplifier (such as in a portable radio transmitter) compensates for fluctuations in ambient temperature, load, signal level and power supply voltage, The control voltage is set by comparing a biasing level which is related to the amplifier input signal level to a voltage proportional to the power supply current of the last stage of the amplifier. The control voltage resulting from the comparison establishes the operating point of the last stage of the power amplifier.

Abstract: An amplifier for a radio transceiver overcomes the problem of gain being dependent on ambient temperature. Transmission power is matched to strength of a received signal by providing matched dual gate FET amplifier stages in both the transmitter and receiver portions of the transceiver. Changes in gain due to temperature are compensated for by detecting changes in the FET drain current by measuring the source voltage of the amplifier. The FET source voltage is compared to a reference voltage, and the output signal resulting from the comparison is provided as a control signal to one of the FET gates.

Abstract: A prescaler input circuit for a frequency converter unit uses a strip line type of directional coupler to isolate the prescaler unit from the frequency converter unit, eliminate beat interference and erroneous frequency dividing operation, and provide a simple and economical structure. The coupler has the prescaler input line inductively coupled to a local oscillator injection element and grounded through a resistor. An earth line is arranged in proximity to the injection lead to provide impedance matching for the coupler.