// SPECTER SDR HELP

IQ Capture and Remote Receivers

Record and replay SigMF IQ baseband, or add rtl_tcp network radios as full SPECTER SDR array elements.

Reviewed September 24, 2026 against source v1.7.41. Features and fixes are labeled by version. Check release availability.

Record raw IQ baseband

IQ capture stores the received radio samples before demodulation. This lets you retune, demodulate, decode, or inspect the same signal later.

  1. Enable ADVANCED in the drawer.
  2. Open SOURCE, then IQ BASEBAND.
  3. Select the receiver and press RECORD IQ.
  4. Press stop when the required signal window is complete.
  5. Use OPEN FOLDER to open Documents\SPECTER SDR\IQ Captures.

Captures use SigMF: cu8 samples in .sigmf-data plus rate, centre frequency, and timestamp in .sigmf-meta. Files can be opened by SigMF-aware tools including SDR++, inspectrum, and gqrx.

Gapless IQ recording reserves the local synchronous USB path for the selected receiver. Other local receivers pause automatically for the capture and resume afterward.

Replay an IQ file

  1. Press PLAY IQ FILE.
  2. Select a cu8 or cf32 capture.
  3. SPECTER restores rate and centre frequency from SigMF metadata when available.
  4. Playback runs at real-time pace and loops at the end of the file.

IQ playback works without an attached receiver, making a saved capture reusable for decoder testing, analysis, and demonstrations.

Add an rtl_tcp receiver

Remote rtl_tcp sources appear as full receiver cards with tuning, gain, sample rate, and PPM controls forwarded to the remote radio.

  1. Start rtl_tcp on the remote machine, for example rtl_tcp -a 0.0.0.0.
  2. Open SETTINGS, then Array & Sources.
  3. Enter one host:port endpoint per line or separate endpoints with commas.
  4. Save Settings. Each source appears as sdr-tcpN in the roster.

Connection drops retry with backoff. Remote receivers can participate in normal tuning, array layouts, linked controls, and scan assignments.

Activity audio is not an IQ capture

The v1.7.40 activity recorder saves demodulated 48 kHz mono WAV audio plus JSON metadata. It does not retain the original RF bandwidth and cannot substitute for SigMF samples when you need to retune or decode later. Plan any exclusive IQ-capture operation around the other receivers whose monitoring would pause.