sjg
182240faa8
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> Signed-off-by: Stan Grams <sjg@haxx.space>
104 lines
3.9 KiB
Markdown
104 lines
3.9 KiB
Markdown
# trx-rs Manual
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## SDR Noise Blanker
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The noise blanker suppresses impulse noise (clicks, pops, ignition interference)
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on raw IQ samples before any mixing or filtering takes place. It works by
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tracking a running RMS level of the signal and replacing any sample whose
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magnitude exceeds **threshold x RMS** with the last known clean sample.
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### Configuration (server-side)
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The noise blanker is configured per rig. In a multi-rig setup each
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`[[rigs]]` entry has its own `[rigs.sdr.noise_blanker]` section:
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```toml
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[[rigs]]
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id = "hf"
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[rigs.rig]
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type = "sdr"
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[rigs.sdr.noise_blanker]
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enabled = true
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threshold = 10.0 # 1 – 100; lower = more aggressive blanking
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```
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For the legacy single-rig (flat) config the path is `[sdr.noise_blanker]`:
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```toml
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[sdr.noise_blanker]
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enabled = true
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threshold = 10.0
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```
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| Field | Type | Default | Range | Description |
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|-------------|-------|---------|---------|-------------|
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| `enabled` | bool | false | — | Turn the noise blanker on or off. |
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| `threshold` | float | 10.0 | 1 – 100 | Multiplier applied to the running RMS. A sample whose magnitude exceeds this multiple is replaced. Lower values blank more aggressively; higher values only catch strong impulses. |
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The noise blanker is off by default.
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### Choosing a threshold
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The threshold controls how aggressively the blanker suppresses impulses.
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A value of **N** means: blank any sample whose magnitude exceeds **N times**
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the running average signal level.
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| Threshold | Behavior | Use case |
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|-----------|----------|----------|
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| 3 – 5 | Very aggressive — blanks frequently | Dense impulse noise (motors, power lines, LED drivers nearby) |
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| 8 – 12 | Moderate — catches clear spikes without touching normal signals | Typical HF conditions with occasional ignition or switching noise |
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| 15 – 25 | Conservative — only blanks strong impulses well above the noise floor | Light interference, or when you want minimal artifacts on weak signals |
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| 30 – 100 | Very light — rarely triggers | Faint, infrequent clicks; mostly a safety net |
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**Start at 10** (the default) and adjust while listening:
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- If impulse noise is still audible, lower the threshold.
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- If weak signals sound choppy or distorted, raise it — the blanker may be
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mistaking signal peaks for noise.
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- On bands with steady atmospheric noise (e.g. 160 m / 80 m), a threshold of
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**5 – 8** usually works well.
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- On quieter VHF/UHF bands where the noise floor is low, values of **15 – 25**
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avoid false triggers from strong signals.
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### Web UI
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When the server reports noise-blanker support, two controls appear in the
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**SDR Settings** row of the web interface:
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- **Noise Blanker** checkbox — enables or disables the blanker in real time.
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- **NB Threshold** number input (1–100) with a **Set** button — adjusts the
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detection threshold. Press Enter or click Set to apply.
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Both controls stay hidden until the server sends filter state containing NB
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fields, so they only appear when connected to an SDR backend.
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### HTTP API
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```
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POST /set_sdr_noise_blanker?enabled=true&threshold=10
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```
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| Parameter | Type | Required | Description |
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|-------------|--------|----------|-------------|
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| `enabled` | bool | yes | `true` or `false` |
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| `threshold` | float | yes | Value between 1 and 100 |
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### How it works
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The blanker runs on every IQ block (4096 samples) *before* the mixer stage in
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the DSP pipeline:
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1. For each sample, compute magnitude² (`re² + im²`).
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2. Compare against `threshold² × mean_sq` (the exponentially-smoothed running
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mean of magnitude²).
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3. If the sample exceeds the threshold, replace it with the previous clean
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sample.
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4. Otherwise, update the running mean with smoothing factor α = 1/128 and store
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the sample as the last clean value.
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Because the blanker operates on raw IQ before frequency translation, it removes
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impulse noise across the entire captured bandwidth regardless of the tuned
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channel offset.
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