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uhf transmitter circuit schematic

UHF Transmitter Circuit

uhf fm transmitterThis UHF transmitter is designed for low power applications as remote for garage doors and operating systems, wireless alarm. This UHF FM transmitter with only one transistor which works on frequencies reserved to low power airwaves signaling.

Transmitters frequency is FM modulated by an audio or digital signal applied in the common point of D1 or D2, through R3. The transmitter schematic can e modified to produce AM modulation by eliminating D1, D2, R2, R3 and R6, and short circuinting A and B points.

Frequency is determined by a resonator, FL1. Can be used the following types:

  • UK: R2528 type for 418MHz
  • SUA: tip R1530 pt 315MHz USA: R1530 tip for 315MHz
  • Olanda, Germania, Belgia: tip R2554 pt 433.92MHz Netherlands, Germany, Belgium type R2554 for 433.92MHz
  • Franta: tip R2523 pt 224.5MHz France: R2523 pt type 224.5MHz

UHF FM transmitter description
T1 transistor is mounted on the front of printed circuit board, as indicated by the dotted line on the drawing board. Also, on the front face of the PCB should be placed either a short connection (silver wire) that connects positive supply bar and inductance L1 made directly on the PCB and parallel to it. Wire position depends on the frequency transmission. Lower frequencies require higher inductance, so connect it farther to PCB edge.

To find the optimum position start by adjusting trimer C3, about the middle range of variation and mount thread connection about half the route that represents inductance. Watch the signal received from the transmitter and adjust until C3 is obtained peak. If you can not find most, try to move the thread to be connected transistor (lower inductance) or to the edge of plate (higher inductance). Optimum position is that the C3 allows obtaining a maximum signal when it is fixed on middle race.

Because we are dealing with a UHF transmitter, it is self understood that all components terminals should be as short as possible. Fm broadcaster should be closed in a plastic so it can radiate.

FM UHF Transmitter circuit diagram

uhf transmitter

UHF transmitter PCB layout

uhf transmitter layout design

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