PURPOSE:To improve an isolation between transmission systems while reducing a loss produced when switching means are turned on by synchronizing the changeover operation of the switching means with the changeover the conversion characteristics of the multiplier of each transmission system. CONSTITUTION:A high frequency signal generated from a high frequency signal generator 2 is amplified 3 in accordance with a modulation signal from a modu lation signal generating circuit 1 and the amplified signal is fed time-divisionally to transmission systems T1-Tn by a switching circuit 4. The signal is multiplied by multipliers 6 (61-6n) in every system T1-Tn. Isolations between the systems T1-Tn due to the presence or absence of the high frequency signal are improved by using the conversion loss characteristics for the bias voltages VB of the multipliers 6. For an above-described improvement, the changeover of the bias voltages VB applied to the multipliers 6 of the systems T1-Tn is executed in synchronism with the switching of diode switches D-SW1 to D-SWn in the circuit 4 under the control of a controller.

High frequency transmitter

PURPOSE:To improve the reliability and reduce the cost by varying a bias resistance of a varactor so as to decrease an output power of a frequency multiplier and isolation of a high frequency switch thereby miniaturizing the high frequency switch. CONSTITUTION:A means varying a bias resistance of the varactor diode 16 is provided. For example, two bias resistors 38, 40 having different resistance and a switch 42 connecting the bias resistors 38, 40 and a coil 14 are provided. Thus, the frequency multiplication efficiency is changed and the isolation of the high frequency switch is decreased in a radio equipment, then the high frequency switch is formed inexpensively and the reliability is improved and miniaturization is attained.

Hario Nobuhiro

Papers

Frequency multiplexing circuit