From 48c4c2dc40690443a155086f940df2b22523dc5a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20Hamal=20Dvo=C5=99=C3=A1k?= <mordae@anilinux.org>
Date: Thu, 6 Jun 2024 20:19:07 +0200
Subject: [PATCH] Remove LO dithering
Means we will probably receive more LO harmonic content but have
better SNR where there is silence.
---
src/main.c | 13 +++----------
1 file changed, 3 insertions(+), 10 deletions(-)
diff --git a/src/main.c b/src/main.c
index 373f198..75ed269 100644
--- a/src/main.c
+++ b/src/main.c
@@ -23,7 +23,6 @@
#define VREG_VOLTAGE VREG_VOLTAGE_1_20
#define CLK_SYS_HZ (300 * MHZ)
-#define LO_DITHER 1
#define PSU_PIN 23
#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)
{
- 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;
for (size_t i = 0; i < len; i++) {
unsigned bits = 0;
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;
-#endif
bits <<= 1;
accum += step;
}