User's Manual

3. CIRCUIT DESCRIPTION
TRANSMITTER
The transmitter is comprised of:
• Audio frequency connections from JP1 pin 1
• Frequency Synthesizer
• Transmitter
Audio frequency connections
In the TX path , audio signal can be send into the chip RDA1846 through AC coupling capacitors.
Frequency synthesizer circuit
With data received from the EEPROM (U3) the frequency synthesizer circuit controls and
Produces the RF carrier frequency for the transmitter during transmit and the local oscillator
frequency for the receiver. The frequency synthesizer circuit is comprised of:
Synthesizer
The U1 (RDA1846) generates the local oscillator and transmitter signal . all building blocks are
fully integrated without any external components. Frequency can be programmed through the serial
interface by the MCU (U3)
26 MHZ TCXO
X1 is VCTCXO, which provide stable oscillator of 26 MHZ to U1.
Frequency adjustment is provided by VR1.
DC REGULATOR
The DC Regulator U4, converts the +6.0 V to a 3.3 V supply . This is used to provide the MCU and U1.
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