This radio remote transmitter circuit works in UHF-FM radio band and can be used for shareholders different systems like garage doors, alarm systems, etc..
Circuit diagram of radio remote transmitter is built using a single transistor and works on a frequency reserved for low power radio waves. Frequency is determined by the resonator, which can be of type FL1 R2528 for 418 MHz to 315 MHz R1530, R2554 to 433.92 MHz, 224.5 MHz R2523 for.
Frequency transmitter is frequency modulated audio signal (or digital) applied to the common point of varicap diodes D1 or D2 by R3.
Scheme can be modified to produce AM modulation (in amplitude) by omitting components D1, D2, R2, R3 and R6 and interconnection points A and B.
On face with soldering of printed circuit board, place a short wire connection (using silver wire) that connects the positive supply bar made directly on the wiring inductance L1 and located parallel to it.
Position of wire connection depends on the emission frequency. As it is lower, the greater the inductance required, so even more will be moved to the edge wire connection.
Optimal position is the C3 allows obtaining maximum signal when attached to the middle of the stroke.