//This is an IQ Mixer made with my knowledge of sdr so far... don't laugh ;-)

//Reads samples from standard input at 1.204Ms/s and writes mixed samples to standard output

//

// to compile: gcc mixer.c -o mixer -lm

//

//rob@m0dts.co.uk

//

//September 2015



#include <stdlib.h>

#include <stdio.h>

#include <math.h>







void main(void){





	int n,i;

	unsigned char inbuf[2];	

	int sample_rate;

	float m1,m2,m3,m4,*vfoi,*vfoq,osc,outbuf[2];

	

	osc = 15000;

	sample_rate = 1024000;

	

	//allocate memory for IQ oscillator lookup table, probably a better way to do it? complex values maybe?

	vfoi= malloc(sample_rate * sizeof(float));

	vfoq= malloc(sample_rate * sizeof(float));

	

	//Create lookup samples for one cycle of oscillator - could use 1/4 cycle... better way?

	for(n=0;n<(sample_rate/(int)osc);n++){

		vfoi[n]=sin((2*M_PI)*osc/sample_rate*n);

		vfoq[n]=cos((2*M_PI)*osc/sample_rate*n);

	}

	

	//IQ mixer - based on 'understanding dsp' book example

	n=0;

	while(1){

		//Read pair of samples

		fread(&inbuf,sizeof(char),2,stdin);

		//I_sample*Q_osc

		m1 = ((float)inbuf[0]-127.0) *vfoq[n];

		//Q_sample*Q_osc

		m2 = ((float)inbuf[1]-127.0) *vfoq[n];

		//Q_sample*I_osc

		m3 = ((float)inbuf[1]-127.0) *-vfoi[n];	// remove '-' for up conversion

		//I_sample*I_osc

		m4 = ((float)inbuf[0]-127.0) *-vfoi[n];	// remove '-' for up conversion

		//sum

		outbuf[0] = m1 - m3;

		outbuf[1] = m2 + m4;

		

		n++;

		if(n==(sample_rate/(int)osc)){n=0;}

		

		//Write pair of samples

		fwrite(&outbuf,sizeof(float),2,stdout);



	}



}