Level App

Introduction

The Level app provides a comprehensive single-screen signal monitoring view combining RSSI meters, a power level readout, receiver saturation indicator, a scrolling history graph, and optionally audio output and an audio squelch beep. It is designed for signal level measurement and monitoring across AM, NFM, WFM, and spectrum (capture) modes.

Controls

Row 1 — gain:

• LNA: Low Noise Amplifier gain (0–40 dB).
• VGA: Variable Gain Amplifier / baseband gain (0–62 dB).
• AMP: RF preamplifier — 0 = off, 1 = on (+14 dB).
• VOL: Audio output volume (only relevant when audio is on).

Row 2 — reception parameters:

• BW: Bandwidth selector. Options depend on the selected modulation mode (AM: DSB/USB/LSB/CW variants; NFM: various kHz widths; WFM: 200k/180k/80k; SPEC: various sampling rates from 12.5k to 20M).
• MODE: Demodulation mode — AM, NFM, WFM, or SPEC. SPEC (spectrum/capture) mode uses the IQ capture baseband and shows signal power without audio demodulation. Cycling past WFM wraps to SPEC, cycling past SPEC wraps back to AM.
• S (Step): Frequency tuning step size for the encoder. A short list of standard step sizes from 100 Hz upward.

Row 3 — frequency:

• Frequency button (labelled ``): click to open the numeric keypad for direct entry. Use the rotary encoder while focused to step in the selected step size.
• The frequency persists from the last used receiver state.

Row 3 (right) — audio:

• AUDIO: audio off / audio on — enables or disables audio output. Audio is not available in SPEC mode even if set to on; in SPEC mode the beep function takes over instead when a signal is above the squelch level.

Row 4 — squelch and display:

• Bip> / beep squelch field: Threshold in dBm (−100 to +20) above which an audio beep is emitted. The beep pitch scales with signal strength: −100 dBm maps to 400 Hz, +20 dBm maps to 2600 Hz, duration 150 ms. The beep fires on every statistics update while the signal exceeds this threshold.
• RSSI: min/avg/max — current RSSI values from the scrolling graph.
• peak: Sets peak hold time for the right vertical RSSI bar — none, 0.25 s, 0.5 s, 1 s, 3 s, 5 s, or 10 s. Default: 0.5 s.
• History columns: Number of columns in the scrolling RSSI/power graph — 16, 32, 64, 128, or 240. Default: 32.

Row 5:

• Power: X db — peak channel power in dB (range −100 to +20).
• RxSat: X% — receiver saturation percentage (see below). Displayed with a colour gradient. Shows RxSat off in WFM+audio mode or SPEC mode where saturation measurement is not available.
• CTCSS tone — in NFM mode, the detected CTCSS/DCS sub-tone or code is shown to the right of RxSat if one is present on the received signal.

Displays

Right vertical level meter

A narrow vertical bar on the right edge of the screen:

• Blue fill — RSSI minimum
• White horizontal bar — RSSI average
• Red fill — RSSI maximum
• Green marker — peak hold (when peak hold is enabled and a peak has been captured)

Scrolling history graph

The main graph area below row 5 shows four overlaid traces over a scrollable history:

• Blue line — RSSI minimum (clipped to RSSI range 31–170, scaled to graph height)
• White line — RSSI average (same range)
• Red line — RSSI maximum (same range)
• Green line — channel power in dB (clipped to −100 to +20 dB, scaled to graph height)

The number of visible history columns is set by the history columns selector.

RxSat colour coding

The RxSat indicator uses a colour gradient to show how hard the receiver front-end is working:

Range	Colour	Meaning
0–80%	Blue → green	Normal — increasing as signal strength grows
80%	Green	Ideal operating point
80–100%	Green → red	Overloading — reduce LNA/VGA gain

RxSat is calculated from the M4 baseband performance counter. It is not available in SPEC mode or in WFM mode with audio enabled.

Modulation modes

Mode	Audio rate	Notes
AM	12 kHz	DSB default. BW selector changes AM configuration (DSB/USB/LSB/CW).
NFM	24 kHz	16 kHz bandwidth default. CTCSS/DCS detection active.
WFM	48 kHz	200 kHz bandwidth default. RxSat not shown when audio is on.
SPEC	24 kHz	IQ capture mode. BW sets the baseband sampling rate. Beep squelch active. No audio.

Settings persistence

The beep squelch threshold, audio on/off state, modulation mode, and bandwidth selection are saved automatically and restored on next launch. Settings are stored in SETTINGS/rx_level.ini on the SD card.

The frequency is not saved in the app's own settings — it follows the global receiver frequency. scaled along the height of the RSSIGraph widget