Frequency modulation circuit for crystal oscillator stabilization in radio transmitter alarm

As shown in the figure, this is a frequency modulation circuit with crystal oscillator stabilization, which is mainly used in radio transmitter alarms. Due to its simplicity, stable performance, small size and low cost, it is a circuit with excellent cost performance.

Performance indicators:

(1) Operating frequency 85～120MHz;

(2) Output power is 5~200mW (adjustable);

(3) Transmission distance: 50 to 1000 m;

(4) Working voltage 9VDC;

(5) Working current: 50~60mA.

Selection and production of components:

The transistors VTl and VT2 are 3DGl30C, β≥50, VT3 is L413K power amplifier tube, and VT4 is 8050, β≥80. The voltage regulator diode VD is 3V, 0.5W voltage regulator tube. ICl is KD-9561 analog soft package audio integrated circuit. Coils Ll~L3 must be made by ourselves. Use Φ1.2mm high-strength enameled wire to tightly wind 6T, 5T, and 4T on a 5mm film mold. After winding, it becomes a hollow coil. All high-frequency circuit oscillation capacitors should use high-frequency ceramic or polyester capacitors. There are no special requirements for other resistors and capacitors. Antenna TX is replaced by 1/4λ plastic multi-strand wire. The antenna length should be 3.125÷4=0.78m (multi-strand plastic wire). Or use a TV pull rod antenna instead. The battery uses two large-capacity 6V batteries connected in series to form a 12V battery.