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)

The noise blanker is configured per rig. In a multi-rig setup each [[rigs]] entry has its own [rigs.sdr.noise_blanker] section:

[[rigs]]
id = "hf"

[rigs.rig]
type = "sdr"

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

For the legacy single-rig (flat) config the path is [sdr.noise_blanker]:

[sdr.noise_blanker]
enabled = true
threshold = 10.0

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.

Choosing a threshold

The threshold controls how aggressively the blanker suppresses impulses. A value of N means: blank any sample whose magnitude exceeds N times the running average signal level.

Threshold	Behavior	Use case
3 – 5	Very aggressive — blanks frequently	Dense impulse noise (motors, power lines, LED drivers nearby)
8 – 12	Moderate — catches clear spikes without touching normal signals	Typical HF conditions with occasional ignition or switching noise
15 – 25	Conservative — only blanks strong impulses well above the noise floor	Light interference, or when you want minimal artifacts on weak signals
30 – 100	Very light — rarely triggers	Faint, infrequent clicks; mostly a safety net

Start at 10 (the default) and adjust while listening:

• If impulse noise is still audible, lower the threshold.
• If weak signals sound choppy or distorted, raise it — the blanker may be mistaking signal peaks for noise.
• On bands with steady atmospheric noise (e.g. 160 m / 80 m), a threshold of 5 – 8 usually works well.
• On quieter VHF/UHF bands where the noise floor is low, values of 15 – 25 avoid false triggers from strong signals.

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.