收发机的发送端完成数字信号和模拟信号合路处理，在同一信道调制发送。收发机的接收端完成接收解调，分离出数字信号和模拟信号，数字信号用数码管显示，模拟信号用示波器观测。

（4） 收发机的信道带宽不大于 25kHz，载波频率范围为 20~30MHz。要求收发机可在不少于 3 个载波频率中选择设置，具体的载波频率自行确定。

（3）在满足基本要求的前提下，收发机所传输的模拟信号频率范围扩展到50Hz~10kHz。

（6）本题目中信道带宽约定为已调信号的 -40dB 带宽，通过频谱仪进行测量。具体如图 2 所示。

如果使用FPGA，可以使用高速比较器 + Sigma Delta实现ADC的功能，能够支持到对语音信号的采样

制定一套简单的协议，标记语音和数据

建议使用10bit/100Msps的DAC，10bit/50Msps也可以用

取样频率50Ksps以上的就可以，模拟带宽要在30MHz以上

Mixer

数据判决

语音/数据 Demux

频率范围在20-30MHz，波长较长～10-15米

普通ADC - 10Ksps/8bit

高速建议：50Msps/10bit

搜索关键词 digital modulator或digital modulation

FPGA-TX can transmit at frequencies of up to 400 MHz and current supports AM, FM, LSB, USB, Wideband FM and Wideband FM Stereo transmission modes. It runs on Linux. The FPGA transmitter has been tested combined together with an amplifier and filter. It can also interface with a GPS unit for clock calibration.

The frequency modulator itself is written in Verilog HDL and is very simple. The project uses an initial frequency of 450 MHz and is almost always divided by 5 with a resulting frequency of 90 MHz. Since for frequency modulation it is necessary to change the frequency within small limits, sometimes after many divisions by 5 the insert “division by 4” is done. The more such inserts, the higher the average frequency of the digital sequence. This is sufficient for the receiver to detect the signal.