BW 1W 数字LCD显示FM发射机

本发射机由微机PIC16F84控制MC145170频率合成器及LCD显示器，电路简单实用。

• 电路图  (pdf文件)
• 元件位置图  (pdf文件)
• 元件清单，装配调试说明
• 改进电路  (pdf文件)
• 照片（另一版本）
• 控制编程：以下程序可供参考。 PIC16F84控制MC145170的程序 RADIOMAX.ASM、PIC84HDR.EQU，频率由上下按钮开关控制，带LCD显示；mc145170.asm和synth170.asm，频率由连接在PIC16F84的RB0:RB7的DIP开关控制，不带LCD显示；由AVR AT90S1200微机控制MC145170频率合成器及LCD显示器的程序plll.asm，plll_def.asm，header.asm。

参考网站：

• http://members.iinet.net.au/~richardh/VK6BRO.htm
• http://www.geocities.com/Area51/Nebula/3736/

电路说明

本发射机采用标准的锁相环频率合成电路。

The voltage controlled oscillator (VCO) is based on a Fairchild MPSH10 NPN bipolar transistor and operates at half the output frequency.  The centre frequency of the VCO is set by an adjustable inductor, which forms a tank circuit with two BB809 varicap diodes.  The first varicap is used as the audio modulator, the second is connected to the output of the PLL loop filter.  This feedback path enables the output frequency to be locked to the frequency of a stable crystal reference oscillator. The audio input circuit is totally passive.  No pre-emphasis is provided, as this unit is designed to be used with a stereo encoder. A small 9V voltage regulator provides a stabilised supply for the VCO and the dc bias for the audio modulating varicap diode.

The output of the VCO is connected to buffer stage based on a MPSH10.  At the output of the buffer, sample of the signal is passed to the f_in input of the synthesiser IC.  Next is the doubler stage, also using a MPSH10.  The output network of this stage is tuned using two variable inductors to pick off the second harmonic of the input signal.  The output device is a trusty old 2N4427 operating in class C. Two more adjustable inductors in its' output network are provided for output tuning. The output matching network incorporates the harmonic filter. The 2N4427 is provided with a push-on aluminium heatsink. No output socket is provided, so a piece of co-axial cable must be soldered to the PCB. A capacitive sniff is taken from the output to a simple rectifier circuit which drives an on-board LED. This allows the circuit to be tuned without additional test-equipment, (apart from a dummy load) by adjusting the adjustable inductors for maximum LED brightness.

The PLL is implemented with the popular (ie lots of pirates use it) Motorola MC145170 PLL frequency synthesiser IC (MC145170).  This synth chip has a three wire serial interface, consisting of data in, clock and enable.  The frequency reference comes from a 8MHz crystal, trimmed by a variable capacitor. The synth chip drives an on board  lock detect LED via a ZTX300 transistor.   The loop reference signal is 50KHz.

The synth chip is programmed by a Microchip Technology PIC16C54 8 bit microcontroller, running off its' internal clock.  This chip is one time programmable, and presumably runs code written by Broadcast Warehouse.   Programming information is derived from a 8 way DIL switch.  This allows the frequency to be set in 100KHz steps, starting from 87.5MHz.  The synth is programmed on power-up and whenever one of the DIL switches is altered.

Another small voltage regulator provides a stabilised 5V supply to the synth and micro-controller chips.

此电路本身不带立体声调制器，你若需要播放立体声节目，请参照这里制作立体声调制器。