trx-rs/MANUAL.md

trx-rs Manual

SDR Noise Blanker

The noise blanker suppresses impulse noise (clicks, pops, ignition interference) on raw IQ samples before any mixing or filtering takes place. It works by tracking a running RMS level of the signal and replacing any sample whose magnitude exceeds threshold x RMS with the last known clean sample.

Configuration (server-side)

Add a [sdr.noise_blanker] section to your trx-server.toml:

[sdr.noise_blanker]
enabled = true
threshold = 10.0     # 1 – 100; lower = more aggressive blanking

Field	Type	Default	Range	Description
enabled	bool	false	—	Turn the noise blanker on or off.
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.

The noise blanker is off by default. A threshold of 10 is a good starting point for typical HF impulse noise. Reduce toward 3–5 for heavy QRM; increase toward 20–30 if weak signals are being clipped.

Web UI

When the server reports noise-blanker support, two controls appear in the SDR Settings row of the web interface:

• Noise Blanker checkbox — enables or disables the blanker in real time.
• NB Threshold number input (1–100) with a Set button — adjusts the detection threshold. Press Enter or click Set to apply.

Both controls stay hidden until the server sends filter state containing NB fields, so they only appear when connected to an SDR backend.

HTTP API

POST /set_sdr_noise_blanker?enabled=true&threshold=10

Parameter	Type	Required	Description
enabled	bool	yes	true or false
threshold	float	yes	Value between 1 and 100

How it works

The blanker runs on every IQ block (4096 samples) before the mixer stage in the DSP pipeline:

1. For each sample, compute magnitude² (re² + im²).
2. Compare against threshold² × mean_sq (the exponentially-smoothed running mean of magnitude²).
3. If the sample exceeds the threshold, replace it with the previous clean sample.
4. Otherwise, update the running mean with smoothing factor α = 1/128 and store the sample as the last clean value.

Because the blanker operates on raw IQ before frequency translation, it removes impulse noise across the entire captured bandwidth regardless of the tuned channel offset.