How do I select a vector signal analyzer for measuring the EVM of a wideband modulated signal?
VSA Selection for EVM
The VSA is the primary instrument for characterizing the modulation quality of any modern wireless transmitter, and its performance directly determines how accurately you can assess the DUT.
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
- Margin allocation: include sufficient design margin to account for manufacturing tolerances and aging effects
Frequently Asked Questions
VSA or oscilloscope for EVM measurement?
VSA (dedicated spectrum/signal analyzer): best EVM floor (0.1-0.5% for high-end), purpose-built demodulation, and efficient workflow. Preferred for production and conformance testing. Oscilloscope + VSA software: wider analysis bandwidth (can exceed 100 GHz), useful when the signal bandwidth exceeds the VSA analysis BW, but typically higher EVM floor (0.5-2% due to 8-10 bit ADC). Preferred for wideband R&D (radar, 5G FR2 with > 1 GHz BW). For most 5G and Wi-Fi testing: a dedicated VSA is the better choice.
How much does a VSA cost?
Entry-level (3 GHz, 40 MHz BW, Wi-Fi/BLE): $15,000-30,000. Mid-range (26.5 GHz, 510 MHz BW, 5G FR1): $50,000-120,000. High-end (50+ GHz, 2 GHz BW, 5G FR2): $150,000-400,000. Demodulation software options: $5,000-30,000 each (5G NR, Wi-Fi 7, LTE, etc.). PXI modular (per channel): $30,000-80,000.
Can I use a VSA for both TX and RX testing?
The VSA is primarily a TX measurement instrument (measures the quality of a transmitted signal). For RX testing: you need a signal generator (VSG) to generate the test signal, and the DUT receiver processes it. The VSA does not generate signals. However: some instruments combine VSA and VSG in one (e.g., Keysight UXM, R&S CMX500 for 5G protocol + RF testing). For production: an integrated VS/VG solution is most efficient.