Time Sink

Time Sink is a time-domain waveform viewer — an oscilloscope for RF. It plots the I (in-phase) component of the received IQ stream as an amplitude-vs-time trace across the screen. Apps like Looking Glass display the frequency domain (spectrum); Time Sink displays the time domain (signal shape over time).

The equivalent GNU Radio block is the Time Sink source block:

Display

The waveform area covers the lower portion of the screen (below the 3-row header). Each horizontal pixel corresponds to one of 240 data points sampled from the received baseband buffer. The vertical axis represents amplitude, with the centre line at zero. Only the I (real) component is shown.

Settings

Row 0 — Frequency and Gain

• Frequency: Default 433.920 MHz. Use the encoder knob or tap to open the keypad.
• Frequency step: Step size for encoder tuning.
• RF Amp (0 or 1): Enables/disables the internal RF amplifier.
• LNA gain (0–40): Low-noise amplifier gain. See Receive Quality Issues.
• VGA gain (0–62): Variable-gain amplifier gain.

Row 1 — Sample Rate and Decimation

• SR (Sample Rate): Baseband sampling rate. Options: 1.0 MHz, 2.0 MHz, 5.0 MHz, 10.0 MHz, 20.0 MHz. Default: 2.0 MHz. Higher rates capture faster signal edges; lower rates give a slower, more zoomed-in time base.
• DEC (Decimation): Range 0–128. Controls how many baseband buffers are skipped between display updates. Each buffer is ~2048 samples. At DEC=0, the display updates every buffer; at DEC=128, it updates every 129th buffer. Increase DEC to slow down the trace refresh on slow or periodic signals.

Row 2 — Persistence and Trigger

• PST (Persistence): Number of past waveform frames to keep visible on screen simultaneously. Options: 1, 2, 4, 8, 16. At PST=1 only the current trace is shown; higher values overlay multiple recent traces, similar to the persistence mode of a digital oscilloscope. Maximum is 16 frames due to memory constraints in the external app format.

• TRM (Trigger Mode): Controls waveform synchronisation.

  • Off — free-running, no synchronisation
  • Rise — triggers on a rising edge crossing the trigger level
  • Fall — triggers on a falling edge crossing the trigger level

  When triggered, the app finds the crossing point in each frame and aligns the display to that position, stabilising the waveform. A ±2 hysteresis band is applied to prevent false triggers. The trigger locks to the nearest crossing to the previous one for frame-to-frame stability.

• LVL (Trigger Level): Range −127 to +127. Sets the amplitude threshold for trigger detection relative to the signal midpoint (0 = centre). Has no effect when TRM is set to Off.

Settings Persistence

All settings (sampling rate, DEC, persistence, trigger mode, trigger level) are saved to rx_time_sink.ini on the SD card when App Settings is enabled in the global Settings menu.