A level detection circuit detects a signal level of an intermediate frequency
signal
which is superposed on a DC voltage input from an input terminal and is separately
extracted by an input processing circuit, and converts the same into a corresponding
DC voltage for output to a transmission output control circuit. The transmission
output control circuit compares the DC voltage received from the level detection
circuit with a reference voltage and determines whether the intermediate frequency
signal is being input. When the transmission output control circuit determines
that the intermediate frequency signal is not being input, a switch circuit cuts
off the power from a power control circuit to a transmission amplifying circuit.
As a result, the radio transmission apparatus can prevent wasteful power consumption
and can suppress a noise and a communication error when the transmission of the
intermediate frequency signal is not intended.
