Ramsey Electronics FM10A - Manual (Page 5)

CIRCUIT DESCRIPTION
A quick glance at the Schematic Diagram shows that the custom FM
stereo transmitter IC (U1) is at the heart of the FM10A. The control of U1 is
determined by its surrounding circuitry. Potentiometers R1 and R4 allow for
adjustment of input level. Resistors R3 and R6 set the pre-emphasis
characteristics (75uS for USA and 50uS for Europe). R7 permits adjustment
of stereo balance. L1 and C16 form an adjustable resonant circuit to set the
carrier operating frequency. Diodes D1,2 and 3 regulate the voltage to U1 at
2.1 volts DC, though Q1 may be operated safely up to 12-15 VDC. The RF
output of Q1 feeds both the on-board whip antenna and J3 for an external
antenna.