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[fix](trx-backend-soapysdr): stabilize WFM signal strength and speed up SDR polling

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Smooth envelope power (I²+Q²) instead of filtering I/Q components
separately — eliminates ~6 dB modulation-dependent fluctuation caused
by FM carrier rotation in the IQ plane. Reset signal strength on
frequency change. Reduce SDR poll interval from 500ms to 100ms.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>
This commit is contained in:
Stan Grams
2026-03-27 18:52:12 +01:00
parent 07cb8818f5
commit d468a96448
2 changed files with 21 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/trx-server/src/main.rs
+4
View File
@@ -1049,6 +1049,10 @@ async fn main() -> DynResult<()> {
);
if let Some(prebuilt) = sdr_prebuilt_rig {
task_config.prebuilt_rig = Some(prebuilt);
// SDR signal strength is a pre-computed field read — no serial
// round-trip — so we can poll much faster than the CAT default.
task_config.polling =
AdaptivePolling::new(Duration::from_millis(100), Duration::from_millis(100));
}
// Spawn rig task.
src/trx-server/trx-backend/trx-backend-soapysdr/src/dsp/channel.rs
+17 -20
View File
@@ -297,18 +297,15 @@ pub struct ChannelDsp {
squelch: VirtualSquelch,
noise_blanker: NoiseBlanker,
last_signal_db: f32,
/// Single-pole IIR states for narrow IQ lowpass (WFM carrier measurement).
/// Filtering the IQ signal (not the power) rejects out-of-band noise so the
/// meter reads carrier level, not total wideband noise power.
/// Single-pole IIR state for smoothed envelope power (WFM signal strength).
carrier_iq_i: f32,
carrier_iq_q: f32,
/// IIR coefficient for the narrow IQ carrier filter, precomputed from sample rate.
/// IIR coefficient for the envelope power smoother, precomputed from sample rate.
carrier_iq_alpha: f32,
}
impl ChannelDsp {
/// Compute the single-pole IIR alpha for narrow IQ carrier measurement.
/// Uses ~500 Hz cutoff so the meter reads carrier level, not wideband noise.
/// Compute the single-pole IIR alpha for envelope power smoothing.
/// Uses ~500 Hz cutoff for a responsive but stable S-meter reading.
fn narrow_carrier_alpha(channel_sample_rate: u32) -> f32 {
const CARRIER_BW_HZ: f32 = 500.0;
if channel_sample_rate == 0 {
@@ -333,6 +330,10 @@ impl ChannelDsp {
} else {
2.0 * std::f64::consts::PI * channel_if_hz / self.sdr_sample_rate as f64
};
// Reset signal strength so the meter doesn't show a stale reading
// from the previous frequency while the IIR catches up.
self.carrier_iq_i = 0.0;
self.last_signal_db = -120.0;
}
fn pipeline_rates(
@@ -427,7 +428,6 @@ impl ChannelDsp {
self.audio_dc = dc_for_mode(&self.mode);
self.carrier_iq_alpha = Self::narrow_carrier_alpha(channel_sample_rate);
self.carrier_iq_i = 0.0;
self.carrier_iq_q = 0.0;
self.frame_buf.clear();
self.frame_buf_offset = 0;
}
@@ -544,7 +544,6 @@ impl ChannelDsp {
noise_blanker: NoiseBlanker::new(nb_cfg.enabled, nb_cfg.threshold),
last_signal_db: -120.0,
carrier_iq_i: 0.0,
carrier_iq_q: 0.0,
carrier_iq_alpha: Self::narrow_carrier_alpha(channel_sample_rate),
}
}
@@ -760,18 +759,17 @@ impl ChannelDsp {
// Signal strength measurement (before AGC).
{
if self.mode == RigMode::WFM {
// WFM: narrow-band carrier measurement via IQ-domain lowpass.
// A single-pole IIR on each of I and Q (≈500 Hz cutoff) rejects
// wideband noise *before* computing power, so the meter reads
// carrier level rather than total noise across the 180 kHz channel.
// WFM: smooth envelope power directly.
// FM is constant-envelope, so I²+Q² is inherently stable
// regardless of modulation content. Averaging power (not I/Q
// components) avoids the ~6 dB dip that occurs when modulation
// rotates the carrier away from DC in the IQ plane.
let alpha = self.carrier_iq_alpha;
for s in decimated.iter() {
self.carrier_iq_i += alpha * (s.re - self.carrier_iq_i);
self.carrier_iq_q += alpha * (s.im - self.carrier_iq_q);
let pwr = s.re * s.re + s.im * s.im;
self.carrier_iq_i += alpha * (pwr - self.carrier_iq_i);
}
let carrier_pwr =
self.carrier_iq_i * self.carrier_iq_i + self.carrier_iq_q * self.carrier_iq_q;
self.last_signal_db = 10.0 * carrier_pwr.max(1e-12).log10();
self.last_signal_db = 10.0 * self.carrier_iq_i.max(1e-12).log10();
} else {
// Other modes: peak IQ magnitude with EMA smoothing.
const SIGNAL_EMA_ALPHA: f32 = 0.4;
@@ -780,8 +778,7 @@ impl ChannelDsp {
.map(|s| s.re * s.re + s.im * s.im)
.fold(0.0_f32, f32::max);
let peak_db = 10.0 * peak_power.max(1e-12).log10();
self.last_signal_db +=
SIGNAL_EMA_ALPHA * (peak_db - self.last_signal_db);
self.last_signal_db += SIGNAL_EMA_ALPHA * (peak_db - self.last_signal_db);
}
}