//Weaver SSB Demod made with my little knowledge of sdr so far.....

//Reads complex samples from standard input at 32KHz and writes demodulated 'real' samples to standard output

//

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

//

//rob@m0dts.co.uk

//

//September 2015



#include <stdlib.h>

#include <stdio.h>

#include <math.h>



#define taps 99



//Coefficients made with http://www.arc.id.au/FilterDesign.html

//LPF 1.4KHz, SR=32k, Atten 60dB, 99 points







float coeff[taps] ={0.000104, 0.000107, 0.000084, 0.000024, -0.000076

, -0.000218, -0.000397, -0.000599, -0.000804, -0.000984, -0.001107, -

0.001139, -0.001046, -0.000803, -0.000394, 0.000180, 0.000898, 

0.001720, 0.002582, 0.003402, 0.004084, 0.004525, 0.004625, 0.004295,

0.003474, 0.002136, 0.000300, -0.001964, -0.004530, -0.007218, -

0.009806, -0.012034, -0.013624, -0.014299, -0.013805, -0.011932, -

0.008534, -0.003551, 0.002985, 0.010937, 0.020069, 0.030052, 0.040479

, 0.050888, 0.060791, 0.069702, 0.077169, 0.082804, 0.086310, 

0.087500, 0.086310, 0.082804, 0.077169, 0.069702, 0.060791, 0.050888,

0.040479, 0.030052, 0.020069, 0.010937, 0.002985, -0.003551, -

0.008534, -0.011932, -0.013805, -0.014299, -0.013624, -0.012034, -

0.009806, -0.007218, -0.004530, -0.001964, 0.000300, 0.002136, 

0.003474, 0.004295, 0.004625, 0.004525, 0.004084, 0.003402, 0.002582,

0.001720, 0.000898, 0.000180, -0.000394, -0.000803, -0.001046, -

0.001139, -0.001107, -0.000984, -0.000804, -0.000599, -0.000397, -

0.000218, -0.000076, 0.000024, 0.000084, 0.000107, 0.000104};





void main(void){





	int n,i,ptr,ptr2,sample_rate,oscsamples;

	float m1,m2,*osci,*oscq,*bufi,*bufq,osc,outbuf,inbuf[2],If,Qf;

	

	osc = 1500;

	sample_rate = 32000;

	oscsamples = sample_rate/(int)osc;

	

	//allocate memory for IQ oscillator lookup table

	osci= malloc(oscsamples * sizeof(float));

	oscq= malloc(oscsamples * sizeof(float));

	

	//Allocate memory for circular input sample buffer, seperate streams

	bufi= malloc(taps * sizeof(float));

	bufq= malloc(taps * sizeof(float));

	

	//Create lookup samples for one cycle of weaver oscillator.....

	for(n=0;n<oscsamples;n++){

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

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

	}

	



	//Loop to read in Complex samples, low pass filter,demodulate SSB,output Real samples

	n=0;

	ptr=0;

	while(1){

		//Read pair of samples

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

		//Split I and Q samples into two buffer streams

		bufi[ptr]= inbuf[0];

		bufq[ptr]= inbuf[1];

		ptr++;

		if(ptr==taps){ptr=0;}

		

		

		//Multiply input samples with coefficients and sum

		If=0;

		Qf=0;

		ptr2=ptr;

		for(i=0;i<taps;i++){

			//filter I and Q stream separately with same coefficients

			If += bufi[ptr2]* coeff[i];

			Qf += bufq[ptr2]* coeff[i];

			ptr2++;

			if(ptr2==taps){ptr2=0;}

		}

		

		

		//Weaver Mix, Add

		m1 = If * osci[n];

		m2 = Qf * oscq[n];



		outbuf = m1 + m2;	// +/- for USB/LSB

		outbuf /=10;

		

		n++;

		if(n==oscsamples){n=0;}	//buffer pointer reset

		

		//Write single sample, real value now

		fwrite(&outbuf,sizeof(float),1,stdout);



	}



}