so its not VSB so what is the function of the last filter?
The filter comprising L1, C12 and C13 is there to filter out the harmonics of the carrier.
Assuming the carrier is at 50 Mhz, there will be harmonics at 100, 150, 200, 250, 300Mhz etc. That filter suppresses those harmonics.
and ya about the AM modulator, where it is ????
Transistors Q5 and Q6 provide a "power amplifier" function, Transistor Q1 effectively controls the collector voltage for Q5 and Q6 creating an amplitude modulator.
The RF output power being (roughly) proportional to the collector voltage.
there is a similar circuit but with transformer ....
maybe it can help u to understand what happend to the audio signal....
Not just "a similar circuit with a transformer", but a circuit with an oscillator which is frequency modulated by the audio. The original circuit just had a bunch of components which did nothing in particular.
This oscillator (Q3 and T1) will be running at whatever frequency (around 5Mhz at a guess) and the output of the oscillator is link coupled by the secondary winding of T1 into the amplitude modulator.
So the resulting output from the antenna will be the carrier frequency (50Mhz), amplitude modulated by:
the video
the audio subcarrier at 5Mhz, which is in turn frequency modulated by the audio.
I have extracted the correct circuit diagram from the Word file so that others can see it easily.
JimB