Analysing GSM Radio Protocol with a Siglent Oscilloscope

This updated case study uses a legacy GSM handset to demonstrate a still-relevant measurement method: correlate analogue baseband activity, radio state changes and supply current on one timebase. The cellular technology is historical, but the workflow applies to modern radios, wireless sensors and battery-powered embedded products.

Treat the handset and its measured values as the worked example, not as a current product recommendation. The reusable lesson is multi-domain correlation.

Signals in the original experiment

Why simultaneous capture matters

A radio event may last only a fraction of the overall duty cycle. A DMM can report average current while missing the peak. A protocol view can show valid traffic without revealing supply collapse or delayed firmware response. Capturing analogue activity and current together links the state transition to its electrical cost.

Recreate the method safely

• Use available documentation and verify the probe points before powering the device.
• Choose a shunt value that produces useful voltage without causing unacceptable burden voltage.
• Use a differential measurement where neither side of the shunt is safely earth referenced.
• Start with conservative bandwidth and probe attenuation, then increase bandwidth only when the event requires it.
• Trigger on a current threshold, zone, radio-control edge or decoded bus event that uniquely identifies the state.
• Use persistence for repeated timing patterns and long memory for infrequent activity.

What to extract from the acquisition

Applying the workflow to current products

For BLE, Wi-Fi, LoRa or other radios, substitute signals that expose the state machine: enable lines, SPI transactions, interrupt pins, RF detector outputs or firmware markers. The oscilloscope does not replace a protocol or vector-signal analyser; it explains when electrical events occur and how they relate to the embedded system.

Recommended instruments