AM transmitter – Nature, Electronics & Robots

I am always interested in building radio circuits. am transmitter, for construction, I used copper clad boards and really like the construction, not neat though, I do remember that I sprayed thicker coats of lacquer on the board before laying the parts on it.

circuit diagram:

back panel

WP_20160322_003 — BNC antenna audio input power DC 12V in

WP_20160323_005 — I used my function generator for carrier signal

WP_20160325_002 — added carrier signal generator (AVR MCU board)

Carrier signal generator program:

it is simple just a PWM code, 16bit timer module in fast PWM

//FUSE bits
/*
BODLEVEL = DISABLED
RSTDISBL = [ ]
DWEN = [ ]
SPIEN = [X]
WDTON = [ ]
EESAVE = [ ]
BOOTSZ = 2048W_3800
BOOTRST = [ ]
CKDIV8 = [ ]
CKOUT = [ ]
SUT_CKSEL = EXTFSXTAL_16KCK_14CK_4MS1

EXTENDED = 0xFF (valid)
HIGH = 0xD9 (valid)
LOW = 0xE7 (valid)
*/
#define F_CPU 16000000UL
#include "avr/io.h"
#include "avr/interrupt.h"
#include "avr/sleep.h"
#include "util/delay.h"
void timer1(void);
void timer1()
{
        /*
         configure the timer1 module fast PWM mode
         Freq_OCR1A_PWM = F_CPU /(N(1+top)) = 16MHz/1(1+top)
         top = ICR1  */
        
    TCCR1A |= 1<<COM1A0 | 1<<WGM10 | 1<<WGM11;
    TCCR1B |= 1<<WGM12 | 1<<WGM13; 
    TCCR1B |= 1<<CS10;
    ICR1 = 27.4;  
}

int main(void)
{
    DDRD = 0x00; 
    PORTD = 0x00; 
    DDRC = 0x00;
    PORTC = 0x00; 
    DDRB |= 1<<PINB1; // declaring PINB1 as output
    timer1(); 
    sei(); //enable interrupt
    while(1)
    { 
        OCR1A = ICR1/2; //50% duty cycle
    }
}

we can also use schmitt trigger for this simple application, i used micrcontroller because i will include SWR meter in the future.