AM transmitter and modulation method using same

A modulation method to be executed by an AM transmitter having an amplifying unit, a detecting signal generating unit, and a gain controlling unit comprising:

• an outputting step of the amplifying unit modulating a carrier wave by a gain controlling signal and amplifying the modulated signal according to the gain controlling signal and outputting a transmitting signal;
• a generating step of the detecting signal generating unit detecting the transmitting signal to generate a detecting signal upon detecting the transmitting signal;
• and
• a controlling step of the gain controlling unit receiving a modulating signal having a level independent from a receiving signal to modulate the carrier wave and comparing a level of the detecting signal with a level of an added signal generated by an addition of a reference signal and the modulating signal and, based on the comparison, generating the gain controlling signal and, based on the generated gain controlling signal, controlling the gain,
• wherein the controlling step further comprises determining, with the gain controlling unit, a difference between a level of the detecting signal and a level of the added signal, and based on the level difference, generating a gain controlling signal that makes the level difference approach zero, and
• the outputting step further comprises an operation of variable gain amplification, with the amplifying unit, to serve as an amplitude-modulation of the carrier wave and power amplification.