The circuit combines 2 audio carrier waves (at 7.02 and 7.2 MHz) with a video signal.
The audio carrier waves are combined in a one transistor common base circuit with an amplification factor 2. Due to the low resistance input at the emitter intermodulation between the 7 MHz audio signals is prevented.
The video signal is fed through a transformer-bridge circuit. The transformer uses a T50-2 Amidon core. This circuit garantees a good seperation between video and audio signals.
November 23 this circuit was succesfully activated in combination with my 13 cm ATV QRP transmitter (with one 7 MHz oscillator). Audio can be improved by a circuit that biases the high audio frequencies. Hope to add the second 7 MHz oscillator on short notice.