mordae/pico-sdr
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Remove LO dithering

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Means we will probably receive more LO harmonic content but have
better SNR where there is silence.
This commit is contained in:
Jan Hamal Dvořák 2024-06-06 20:19:07 +02:00
parent 7e41420d14
commit 48c4c2dc40
1 changed files with 3 additions and 10 deletions

13
src/main.c
View file

@ -23,7 +23,6 @@
#define VREG_VOLTAGE VREG_VOLTAGE_1_20 #define VREG_VOLTAGE VREG_VOLTAGE_1_20
#define CLK_SYS_HZ (300 * MHZ) #define CLK_SYS_HZ (300 * MHZ)
#define LO_DITHER 1
#define PSU_PIN 23 #define PSU_PIN 23
#define IQ_SAMPLES 32 #define IQ_SAMPLES 32
@ -202,22 +201,16 @@ static void adder_init()
static void lo_generate(uint32_t *buf, size_t len, double freq, unsigned phase) static void lo_generate(uint32_t *buf, size_t len, double freq, unsigned phase)
{ {
unsigned step = ((double)UINT_MAX + 1.0) / (double)CLK_SYS_HZ * freq; static const double base = (UINT_MAX + 1.0) / CLK_SYS_HZ;
unsigned step = base * freq;
unsigned accum = phase; unsigned accum = phase;
for (size_t i = 0; i < len; i++) { for (size_t i = 0; i < len; i++) {
unsigned bits = 0; unsigned bits = 0;
for (int j = 0; j < 32; j++) { for (int j = 0; j < 32; j++) {
#if LO_DITHER
int n0 = rand() - RAND_MAX / 2;
int n1 = rand() - RAND_MAX / 2;
int noise = (n0 + n1) / 2;
bits |= (accum + noise) >> 31;
#else
bits |= accum >> 31; bits |= accum >> 31;
#endif
bits <<= 1; bits <<= 1;
accum += step; accum += step;
} }