The low-frequency signal through the transformer TR1 is the effect on the high frequency signal. When using the quartz frequency is 8 MHz modulated signals is good you will hear on the eighteenth harmonic (144 MHz). Type of modulation in this case is a mix between AM and FM.
The frequency of the modulating signal generator to about 1 kHz. The resistance of the primary winding of the transformer 300 - 500 Ohms, and the secondary - 2.5 to 8 Ohms. Choke DR1 wound on a resistor of 100 Ohms.
Transistor AS can be replaced by P. and AS-MPA. Choke DR1 should have an inductance of about 100-500 uh. As the transformer TR1 can use a output transformer from a pocket transistor radios.
Literature
Publication: N. Bolshakov, rf.atnn.ru