4. System Context (APP 011)

4.1 Context Diagram

HAM Operator
  |
  | HTTPS/WSS from mobile or desktop browser
  v
SunMRRC FastAPI Server
  | serves static UI
  | manages WebSocket clients
  | imports SunSDR protocol and DSP helpers
  |
  | UDP control 192.168.16.100:50001 -> 192.168.16.200:50001
  | UDP IQ bind 192.168.16.100:50002 <- SunSDR2 DX stream
  v
SunSDR2 DX

4.2 Actors

Actor	Role
HAM Operator	Uses browser UI to listen, tune, adjust DSP/gain/filter, key PTT, and monitor status
System Maintainer	Starts/restarts service, manages TLS certificates, checks logs, validates network routing
SunSDR2 DX	External radio device controlled through verified UDP binary protocol
Browser Runtime	Provides WebSocket, Web Audio, microphone APIs, touch input, service worker cache

4.3 External Interfaces

Interface	Protocol	Endpoint	Direction	Description
Static UI	HTTPS/HTTP	`/{p:path}`	Browser -> Server	Serves `index.html`, CSS, JS, manifest, images, wasm
Control WebSocket	WSS/WS	`/WSCTRX`	Browser <-> Server	Commands and state updates
RX Audio WebSocket	WSS/WS	`/WSaudioRX`	Server -> Browser	Tagged dual-codec audio frames (1-byte tag: 0x00=Int16 PCM, 0x01=Opus 16 kHz mono; default Opus)
TX Audio WebSocket	WSS/WS	`/WSaudioTX`	Browser -> Server	Tagged Opus/PCM mic frames modulated to SunSDR TX IQ (`0xFFFD`)
Spectrum WebSocket	WSS/WS	`/WSspectrum`	Server -> Browser	Quantized spectrum rows
Band Power API	HTTPS/HTTP	`/api/band_power`	Browser <-> Server	Get/set per-band TX drive %, persisted to `band_power.json`
Memory Channel API	HTTPS/HTTP	`/api/mem_channels`	Browser <-> Server	Get/set memory channels, persisted to `mem_channels.json`
SunSDR Control	UDP	device `:50001`	Server <-> Radio	Boot, frequency, PTT, drive/power, gain, filter, tune commands
SunSDR IQ Stream	UDP	local bind `:50002`	Radio -> Server	24-bit IQ packet stream, plus keepalive/control packets
TLS Certificate	File	`certs/fullchain.pem`, `certs/radio.vlsc.net.key`	Server local	HTTPS enablement

4.4 Data Flows

Flow	Description
RX signal flow	SunSDR IQ UDP -> decode 24-bit IQ -> DSP feed -> demodulated PCM -> resample to 16 kHz -> `/WSaudioRX` -> Web Audio playback
Spectrum flow	IQ -> FFT -> dB clip -> uint8 quantize (512 bytes, ~38 Hz) -> `/WSspectrum` -> client accumulates `WF_DECIMATE` frames (~3.8 Hz) -> per-row adaptive noise floor (`WF_PCTL`) + blue-sea bias (`WF_BIAS`) + gain (`WF_GAIN`) -> waterfall canvas
Control flow	UI action -> `/WSCTRX` command string -> `SunSDR2DXClient` or demodulator setter -> response/broadcast
TX voice flow	Browser mic -> `/WSaudioTX` tagged Opus/PCM -> server codec decode -> `TXModulator` resample to 15625 Hz -> Hilbert SSB -> 24-bit IQ -> `0xFFFD` packets paced to device `:50002`
TX power flow	`setDrive:*` or QSY → `band_power_for(freq)` → DRIVE command (`0x0017`, byte in trailing word) → device per-band power; re-sent before each PTT assert
TX telemetry flow	Device `0x1F00` (34B) continuous in RX and TX → off30 f32 forward watts, off16 u16/10 supply volts, off18 f32 PA temp °C → `getTXTelem:W,V,T,WattInt` over `/WSCTRX` → frontend VOLT field (replaces former SWR). No device reverse-power → no SWR.
TX audio gain flow	Client preamp(×1.5) → EQ(6-12dB peaks) → AudioWorklet 48k→16k → Opus/PCM → WSaudioTX → server TXModulator → Hilbert SSB → drive gain(×3.0×drive%) → tanh(1.0) soft limiter → 24-bit IQ. tanh engagement ~4% at healthy levels.
Liveness/latency flow	Frontend sends no-colon `PING` -> `ws_ctrl()` answers `PONG` before command parsing -> frontend round-trip timer updates the status-bar latency (ms)
S-meter flow	FFT percentile -> `getSignalLevel:*` over `/WSCTRX` -> client asymmetric exponential smoothing (attack 0.5 / release 0.15) -> S-meter needle
PTT safety flow	UI PTT press/release -> `setPTT:` -> radio PTT -> `getPTT:` ack -> frontend retry/watchdog when release ack is missing
HTTPS flow	Uvicorn selects TLS cert/key at startup; frontend selects WSS when page protocol is HTTPS

4.5 System Boundaries

Boundary	Inside	Outside
Browser boundary	UI state, audio playback, mic capture, PTT safety UX	Browser permission model and autoplay policy
Server boundary	WebSockets, static serving, IQ processing orchestration, TLS startup	Radio firmware, network routing, certificate issuance
Shared-code boundary	`../web_control/sunsdr_direct.py`, `dsp.py`, `wdsp_wrapper.py`	These are imported dependencies rather than local `sunmrrc` files
Device boundary	UDP packets sent/received by server	SunSDR2 DX hardware behavior and RF environment

4.6 Contextual Constraints

iOS Safari requires HTTPS for reliable getUserMedia and AudioContext behavior outside localhost.
The current server binds SunSDR local UDP addresses directly as 192.168.16.100, so deployment network topology is part of the design.
The default radio host is 192.168.16.200, configurable by DEVICE_HOST only for the control client; IQ bind/send paths still contain fixed addresses in server.py.
/WSATR1000 is not part of the current backend despite frontend references.