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Looking Glass

Introduction

Looking Glass provides a wide-band spectrum waterfall view covering a large frequency range in a single scrolling display. The HackRF steps through the configured range in slices, and each completed full sweep updates the waterfall with a new row.

For wide scan ranges the sweep time is long and the display may appear frozen — this is normal. Keep the scan range as small as practical to get fast, responsive updates. Despite the HackRF's modest sensitivity, Looking Glass is a useful tool for spotting local RF activity across a broad span when paired with an appropriate antenna.

Frequency presets are stored on the SD card at LOOKINGGLASS/PRESETS.TXT. Keep preset ranges small to limit memory usage.

Controls

• MIN / MAX: Place the cursor on the MIN or MAX field and use the rotary encoder to adjust the lower or upper scan frequency in steps of the selected step size. The RANGE label shows the total scan span.

• Range lock: Click on the range value label to lock or unlock the range width when adjusting MIN/MAX. When locked, moving MIN also moves MAX so the span stays fixed.

• PRESET: Move the cursor to the PRESET: field to select one of the pre-set frequency ranges from LOOKINGGLASS/PRESETS.TXT on the SD card.

• LNA / VGA / AMP: Gain controls. LNA (IF) adjustable 0–40 dB; VGA (baseband) 0–62 dB; AMP 0 = off, 1 = on (+14 dB).

• FILTER: Selects a display smoothing filter — OFF, MID, or HIGH. The filter affects the visual contrast of detected signals. Adjust to get the best contrast for the signals you are trying to see; the optimal setting depends on scan speed and gain.

• F- / S-: Scan mode — F- is fast but less accurate; S- is slow but more accurate.

• SPECTR / LIVE-V / PEAK-V: Selects the display mode:

  • SPECTR — scrolling waterfall (default)
  • LIVE-V — live frequency power level bars
  • PEAK-V — peak frequency power level bars

• RES: Resolution (FFT trigger point), adjustable 2–128. Default is 32. Increase for finer frequency resolution; decrease for faster updates. Adjust together with gain and FILTER for best results.

• MARKER: Rotate the encoder while the cursor is on this field to move a red frequency marker arrow across the waterfall display. The marker's frequency and the per-pixel frequency step are shown. Pressing the encoder knob or the button jumps to the Audio app at the marker frequency with 1 MHz steps and a 10 MHz view. Note: returning from the Audio app resets Looking Glass to its default settings.

• BEEP: Click to enable or disable the audio squelch beep. When enabled, a beep is emitted whenever signal power at the marker exceeds the configured squelch threshold (adjustable from −100 to +20 dB; default is 20, which disables it).

• VOL: Controls the volume of the beep when beep is enabled.

• RXIQCAL: IQ calibration for the receiver's image rejection ratio (IRR). This calibration only applies to zero-IF tuning apps such as Looking Glass and the Audio app in SPECTRUM mode. The calibrated value is stored in SETTINGS/rx_glass.ini. A good starting point is the central value: 15/32 on non-r9 HackRF devices (MAX2837), or 31/64 on r9 devices (MAX2839). A well-chosen calibration value can improve image rejection by 8–10 dB compared to the worst-case setting.

LIVE-V and PEAK-V additional controls

When LIVE-V or PEAK-V mode is selected, two additional controls appear along with a MAX HOLD: VALUE line:

• x0 – x9 (LIVE-V only): Integration multiplier. x0 gives the fastest response with more noise; x9 gives the slowest, smoothest response with fewer spikes.

• RST: Resets the peak-hold value and clears the display.

• JMP: Jumps to the Audio app at the frequency shown in MAX HOLD.