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Fix max amplitude formula and DC bias removal

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This commit is contained in:
Jan Hamal Dvořák 2024-02-24 22:26:09 +01:00
parent 3f8b2846bd
commit 34c070ed42
1 changed files with 25 additions and 9 deletions
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34
src/main.c
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@ -551,7 +551,11 @@ static void rf_rx(void)
int64_t dcI = 0, dcQ = 0;
const int amp_max = (float)CLK_SYS_HZ / BANDWIDTH * DECIMATION * 3.0 / 4.0 / 2.0;
/*
* CLK / BW for oversampling, but 1/2 for the -1/0/0/1 PIO outcomes.
* Signal can get outside due to DC offset compensation.
*/
const int amp_max = CLK_SYS_HZ / 2 / BANDWIDTH * DECIMATION;
while (true) {
if (multicore_fifo_rvalid()) {
@ -619,16 +623,28 @@ static void rf_rx(void)
I = lpIa3 / LPF_SIZE;
Q = lpQa3 / LPF_SIZE;
int64_t I64 = (int64_t)I << 32;
int64_t Q64 = (int64_t)Q << 32;
dI += (I64 - dcI) >> 32;
dQ += (Q64 - dcQ) >> 32;
dcI = ((dcI << 20) - dcI + I64) >> 20;
dcQ = ((dcQ << 20) - dcQ + Q64) >> 20;
dI += I;
dQ += Q;
}
dcI = ((dcI << 13) - dcI + (dI << 19)) >> 13;
dcQ = ((dcQ << 13) - dcQ + (dQ << 19)) >> 13;
dI -= dcI >> 19;
dQ -= dcQ >> 19;
if (dI > amp_max)
dI = amp_max;
if (dI < -amp_max)
dI = -amp_max;
if (dQ > amp_max)
dQ = amp_max;
if (dQ < -amp_max)
dQ = -amp_max;
*blockptr++ = 127 * dI / amp_max;
*blockptr++ = 127 * dQ / amp_max;
}