Swept Scanning vs Continuous I/Q Recording

[Pavel]

Short answer: Swept scanning covers more spectrum with less data but observes each frequency only during brief dwell periods. Continuous I/Q preserves every event inside its instantaneous bandwidth and phase information, at far greater storage and processing cost.

Before you start​

• Define authorized bands, observation period, minimum signal duration and the measurement you need before selecting hardware.
• Use shielding or conducted RF paths for active security tests whenever over-the-air transmission is unnecessary.

Step-by-step method​

1. Step 1: Define the shortest event and required detection probability. Compare scanner revisit time with event duration; events shorter than the revisit gap can be missed completely.
2. Step 2: For sweeping, set span, step size, dwell, resolution bandwidth and overlap so narrow signals are not skipped between bins.
3. Step 3: For I/Q, calculate complex sample format, sample rate and duration, then benchmark disk throughput with margin. Preserve sample-rate and clock metadata.
4. Step 4: Run both methods on a controlled intermittent source and compare detections, amplitude error and data volume before selecting the deployment.

Concrete example​

A scanner revisiting a channel every two seconds may never see a 50 ms burst. A continuous 10 MSPS 16-bit I plus 16-bit Q stream produces about 40 MB/s before metadata, or roughly 144 GB per hour.

How to judge the result​

Choose sweeping when broad occupancy trends tolerate missed short events; choose continuous I/Q when waveform, timing or guaranteed in-band capture matters.

What to record​

• Calibrate amplitude with a known source and record frequency-dependent correction; an SDR display is not automatically a traceable power meter.
• Store enough metadata to reproduce each observation: receiver, clock, antenna, gain, bandwidth, location precision and software configuration.
• For occupancy, define threshold, time resolution and treatment of noise before calculating percentages.

Common mistakes​

• Changing several hardware, software or RF variables at once, which removes the controlled comparison needed to identify the cause.
• Treating one autoscaled screenshot or one unusually good result as proof without recording the settings and repeating the test.
• Calling a sweep continuous monitoring hides the blind time between visits to each frequency.

Final check​

Run a known controlled signal through the monitoring method and verify detection, calibration, timestamps and gaps. Keep authorization and data-handling records with the measurement.