A transmission system or apparatus includes a transmitter or source of transmitted RF or microwave power which is selectively connectable via a transmitter connector to an antenna having an antenna feed via an antenna connector so that a variety of antennas with differing characteristics can be used with a given transmitter. Each antenna preferably has a marker or indicating element incorporated into the antenna feed. The marker or indicating element includes a physically measurable property or parameter corresponding to a physical characteristic of the attached antenna. In the preferred embodiment, the indicating element is a resistance connected in parallel with the antenna feed and having a selected resistance value (e.g., in ohms) which indicates the physical characteristic of gain for antenna. The transmission system also includes an indicating element sensor configured to sense or measure the marker or indicating element and generate a transmitter control signal in response to that measurement. The method for automatically generating the control signal can be implemented in programmable steps as computer software and may include use of a Look Up Table (LUT) having a range of indicator element characteristic values and a range of corresponding transmitter control signal values or, alternatively, can include use of a computation sequence which takes an indicator element characteristic value as an input variable and generates a control signal value in response thereto.