IQ analyzer - voxo22/hackrf-spectrum-analyzer GitHub Wiki

The I/Q analyzer is used for time-domain analysis of a selected signal or replayed I/Q recording. It can show raw I/Q samples, envelope, deviation, trigger state, burst activity and the selected channel spectrum.

You can navigate into I/Q analyzer screen by dragging with RIGHT mouse button or by double click the RIGHT mouse button from spectrum analyzer (red highlight). Spectrum analyzer has to be in the LIVE capture mode, or in WAV/PCM/CU8 REPLAY mode.

Time-domain display

time-domain_display

The main time-domain display shows incoming I/Q samples or processed views of the selected channel.

The LIVE time-domain view is limited by HackRF bandwidth. In I/Q replay mode, the analyzer can use the full recorded bandwidth of the WAV/PCM/CU8 file.

The upper status row shows current time-view parameters and the RMS/PEAK level meter. The level meter is important when setting levels for I/Q recording or signal analysis. Avoid red peak levels, because clipped samples can damage later analysis.

Mouse controls:

  • Mouse wheel zooms the time view.
  • The + and - buttons change zoom from the right side of the display.
  • LEFT click displays delta time measurement from the pre-trigger marker.
  • LEFT drag measures delta time between any two points.
  • RIGHT click clears measurement display.

When burst trigger is enabled, the trigger level is shown as an orange dashed line and trigger state is displayed in the upper right part of the time-domain view.

I/Q spectrum display

IQ_channel_spectrum_display

The I/Q spectrum display shows the selected source or channel spectrum. Drag the spectrum to adjust the exact channel offset. The selected channel bandwidth is shown as a highlighted part of the spectrum.

RF controls

The RF panel contains receiver center frequency, sample rate and HackRF gain controls.

  • Center frequency sets the receiver center frequency for time-domain analysis. In live capture mode it can be corrected manually.
  • Sample rate controls HackRF I/Q sample rate. Higher rates cover more bandwidth but require more processing.
  • LNA gain is received from the spectrum sweep and can be adjusted manually.
  • VGA gain defaults to 32 and can be adjusted for fine control of peak levels.
  • RF AMP enables the HackRF's internal RF pre-amp. Use carefully, because strong signals can overload or damage the RF front end.

View and channel controls

Wideband mode analyzes the whole source. Narrowband mode extracts a channel around the selected offset and is useful for bandwidths below 2 MHz, because 2 Msps is the lowest HackRF sample rate.

Channel offset is relative to the receiver center frequency. It can be adjusted by dragging the spectrum display or entering a specific value.

DC offset avoidance moves the selected channel away from the center DC artifact. Low-IF shift is calculated automatically in Narrowband mode; in Wideband mode it can be adjusted manually up to half the bandwidth.

Bandwidth defines the channel bandwidth used for filtering, demodulation, recordings and signal analysis.

Output rate is the sample rate after channel filtering. It can reduce the amount of data and processing for recording or demodulation.

Signal analysis

Signal analyzer mode selects the decoder or signal type used by the Signal Analyzer.

The ANALYZE button opens the Signal Analyzer for the selected signal type. While its window is open, the button changes to SHOW and brings that window to the foreground.

For more info about analyzer see also: Signal analyzer.

Views and overlays

  • Envelope shows the amplitude envelope instead of raw I/Q waveform detail.
  • When Envelope is disabled, the display shows raw I/Q waveform detail: I component in green and Q component in red.
  • Burst highlights burst-like activity as orange overline above the I/Q envelope.
  • Burst statistics show number of bursts, interval/frequency and width in the current window.

FSK_dev

FSK Dev shows FSK/FM deviation as a violet line.

Auto level

Auto level automatically scales RMS signal level for a readable time-domain view.

Use it carefully. Auto level does not affect level for the Signal Analyzer, but it does affect I/Q recording and demodulation, and it can clip peaks. Watch the RMS/PEAK level meter to avoid clipping.

Recording and audio

AUDIO REC button saves demodulated audio to a 16-bit, 48 kHz WAV file. The file is saved to the root folder.

VIDEO REC button records the I/Q analyzer window to video. MP4 can include demodulated audio. GIF is suitable only for short clips. The file is saved to the root folder.

IQ REC button saves filtered I/Q samples to a WAV/PCM-style I/Q file. Recorded WAV, PCM, and CU8 I/Q files can be replayed later with the REPLAY button in the spectrum analyzer. The file is saved to the root folder.

Note: AUTO LEVEL affects the level of recorded I/Q samples, so it should normally be disabled for proper I/Q recording.

Trigger

Burst trigger detection can be enabled for the time-domain view. The trigger state is shown in the upper right corner of the display.

Single trigger arms a one-shot capture. When a trigger event is detected, the time-domain view stops and displays the captured signal. Changing trigger settings or zoom automatically re-arms the one-shot trigger.

Pre-trigger history controls how much signal before the trigger event is retained.

Trigger level controls burst sensitivity. Lower values are more sensitive. The trigger level is displayed as an orange dashed line.