[docs](trx-rs): document SoapySDR squelch settings

Co-authored-by: OpenAI Codex <codex@openai.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

aidocs/CONFIGURATION.md

@@ -122,6 +122,12 @@ Notes:
 - `mode` (`string`, default: `"auto"`): `"auto"` enables hardware AGC (falls back to `"manual"` with a warning if the device does not support it); `"manual"` uses the fixed `value`.
 - `value` (`f64`, default: `30.0`): Gain in dB. Used only when `mode = "manual"`.
 
+### `[sdr.squelch]`
+- `enabled` (`bool`, default: `false`): Enables virtual software squelch for demodulated audio except WFM on the primary SDR channel.
+- `threshold_db` (`f32`, default: `-65.0`, valid: `-140..=0`): Open threshold in dBFS.
+- `hysteresis_db` (`f32`, default: `3.0`, valid: `0..=40`): Close hysteresis in dB.
+- `tail_ms` (`u32`, default: `180`, valid: `0..=10000`): Tail hold time after signal drops below threshold.
+
 ### `[[sdr.channels]]`
 
 Defines one virtual receiver channel within the wideband IQ stream. At least one channel is required when using the `soapysdr` backend. The **first** channel in the list is the *primary* channel: `set_freq` and `set_mode` from rig control apply to it, and `get_status` reads from it.

aidocs/SDR.md

@@ -224,6 +224,18 @@ value = 30.0      # dB; ignored when mode = "auto"
 
 Advanced per-element gain is out of scope for this phase (no `lna`/`vga`/`if` sub-keys initially).
 
+### 4.1 Virtual Squelch
+
+Software squelch is configured globally under `[sdr.squelch]` and currently applies to the primary channel's demodulated audio path except WFM.
+
+```toml
+[sdr.squelch]
+enabled       = false
+threshold_db  = -65.0   # dBFS open threshold
+hysteresis_db = 3.0     # dB close hysteresis
+tail_ms       = 180     # hold time after signal drops
+```
+
 ---
 
 ## 5. Filter Configuration
@@ -311,6 +323,12 @@ center_offset_hz = 200000      # SDR tunes this many Hz below dial frequency
 mode  = "auto"
 value = 30.0                   # Effective only when mode = "manual"
 
+[sdr.squelch]
+enabled       = false
+threshold_db  = -65.0
+hysteresis_db = 3.0
+tail_ms       = 180
+
 [[sdr.channels]]
 id               = "primary"
 offset_hz        = 0

trx-rs.toml.example

@@ -128,6 +128,12 @@ wspr_file = "TRXRS-WSPR-%YYYY%-%MM%-%DD%.log"
 # mode  = "auto"
 # value = 30.0
 #
+# [trx-server.sdr.squelch]
+# enabled       = false
+# threshold_db  = -65.0
+# hysteresis_db = 3.0
+# tail_ms       = 180
+#
 # [[trx-server.sdr.channels]]
 # id               = "primary"
 # offset_hz        = 0