The RDA1846S transceiver features very low solution cost and reduced complexity. As shown in Fig.3.1，

　　to totally complete the translation from RF carrier to voice in the RX path and from voice to RF carrier in

　　the TX path， the chip integrates nearly all the functional blocks including RF and base band analog blocks

　　and digital signal processor. It requires only one micro controller and a few external components to

　　realize a walkie-talkie.

　　A powerful integrated DSP accomplishes both the demodulation and modulation of the FM signal.

　　Besides， standard walkie-talkie features such as CTS， CDS， VOX and SQ etc. are provided through the 8

　　GPIOs of the chip. Especially， by virtue of the state-of-the-art CMOS technology advanced algorithms

　　such as AFC， AGC， RSSI and SNR calculations are realized in the DSP， which guarantees the high

　　receiving and transmitting quality while still consumes a low power. Flexible RX/TX/SLEEP auto switching

　　function from the DSP further reduces the average power consumptions.

　　LDOs are also integrated in the chip which further reduces the BOMs.

　　All interface pins of the chip will be shortly explained below. For details， refer to the ‘RDA 1846

　　programming guide’。

　　3.1 RF input and output

　　The chip can receive and transmit RF signals from 400 to 500MHz and from 134 to 174MHz which cover

　　most of the walkie-talkie frequency bands around the world and the weather broadcast band. For the RF

　　input， a direct-in connection from the antenna to the LNA input pin through a switch is suggested which

　　means no input impedance matching is needed for the receive band. For the RF out， a pa diver can

　　deliver no more than 8 dBm power to PA. PA bias voltage from 1.5V~2.8V for the power amplifier can be

　　supplied from the PABIAS pin.