How do I measure the adjacent channel power of a transmitter using a spectrum analyzer?
Adjacent Channel Power Measurement
ACLR measurement is the most common linearity test for modern wireless transmitters. It directly indicates how much spectral regrowth (caused by PA nonlinearity) is leaking into adjacent channels.
| Parameter | Option A | Option B | Option C |
|---|---|---|---|
| Performance | High | Medium | Low |
| Cost | High | Low | Medium |
| Complexity | High | Low | Medium |
| Bandwidth | Narrow | Wide | Moderate |
| Typical Use | Lab/military | Consumer | Industrial |
Technical Considerations
When evaluating measure the adjacent channel power of a transmitter using a spectrum analyzer?, engineers must account for the specific requirements of their target application. The optimal choice depends on the frequency range, power level, environmental conditions, and cost constraints of the overall system design.
Performance Analysis
When evaluating measure the adjacent channel power of a transmitter using a spectrum analyzer?, engineers must account for the specific requirements of their target application. The optimal choice depends on the frequency range, power level, environmental conditions, and cost constraints of the overall system design.
- 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
Design Guidelines
When evaluating measure the adjacent channel power of a transmitter using a spectrum analyzer?, engineers must account for the specific requirements of their target application. The optimal choice depends on the frequency range, power level, environmental conditions, and cost constraints of the overall system design.
Frequently Asked Questions
What limits the ACLR measurement accuracy?
The spectrum analyzer's own dynamic range limits the measurable ACLR. Sources of measurement error: analyzer noise floor (if the adjacent channel power is near the analyzer noise floor, the measurement reads higher than the true ACLR; use lower RBW or averaging to reduce the noise floor), analyzer phase noise (the analyzer's LO phase noise spreads the main channel power into adjacent channels, creating a false ACLR floor; high-performance analyzers have ACLR measurement floors of -70 to -80 dBc), and analyzer intermodulation (the analyzer's own input mixer can create IM products that corrupt the measurement; increase the analyzer's input attenuation to reduce the signal level at the mixer).
Should I use a modulated or CW signal?
ACLR must be measured with the actual modulated signal (or a representative test signal) because the spectral regrowth depends on the signal's peak-to-average power ratio (PAPR), modulation bandwidth, and statistical properties. A CW signal produces no adjacent channel power. A two-tone test produces IMD products but does not accurately represent the spectral regrowth of a modulated signal. Use the standard-specified test signal: for 5G NR, use a fully allocated OFDM signal with the specified modulation, bandwidth, and numerology.
What about spectrum emission mask measurements?
In addition to ACLR: wireless standards specify a spectrum emission mask (SEM) that defines the maximum allowable PSD at every frequency offset from the carrier. The SEM is measured on the same spectrum analyzer setup as ACLR, but the result is compared to a frequency-dependent limit line rather than a single channel power ratio. The analyzer's SEM measurement function displays the measured spectrum with the mask overlay and reports pass/fail at each defined offset. SEM is more comprehensive than ACLR because it covers all offsets, not just the adjacent channels.