BK Radio
Page 4-3
theory of operation
rf input/output
The RF input / output section consists of the Harmonic Filter and the Antenna Switch.
Tx / Rx
Antenna
Switch
Harmonic
Filter
Rx
Tx
rf input/output Block diagram
The Harmonic Filter provides low-pass filtering for both the transmitter and the receiver. For the
receiver, the filter rejects undesired image/spurious frequencies. For the transmitter, the filter attenuates
harmonics of the RF signal which would otherwise be transmitted.
The Antenna Switch is a low loss RF switch that normally connects the antenna to the receiver input. It
connects the antenna to the transmitter section whenever the push-to-talk (PTT) button is pressed. It
also isolates the TX signal from the receiver to prevent damage to the lower power receiver circuits.
Synthesizer
The Synthesizer section has circuits that perform many functions including frequency generation,
modulation and buffering. The main functional blocks in the transmitter are:
• TCXO frequency reference
• Synthesizer IC
• Loop Filter
• Rx VCO
• Tx VCO
• Digital Potentiometer
• VCO Buffer
Rx VCO
VCO Buffer
Loop Filter
Programming
Bus
Synthesizer
IC
Tx VCO
Steering Line
Tx Audio
Coarse Tune
TCXO
Reference
10 MHz
Tx / Rx
Tx / Rx
Coarse Tune
Control
Digital
Potentiometer
SPI
LO
Coarse Tune
DAC
From uP
RX VCO
181-219 MHz (P150)
290-380 MHz (P400)
350-430 MHz (P500)
TX VCO
136-174 MHz (P150)
380-470 MHz (P400)
440-520 MHz (P500)
Synthesizer Block diagram
Summary of Contents for P150
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