CW
Understanding CW Signals
CW signals are the simplest possible RF signals: a pure sinusoid at a single frequency with constant amplitude. While real communication signals are always modulated, CW signals serve as the fundamental reference for characterizing RF components and systems.
CW vs Modulated Signals
- Power measurement: CW power is well-defined (average = peak). For modulated signals, average, peak, and RMS power differ.
- P1dB and IP3: Specified with CW test signals. Performance with modulated waveforms (high PAPR) differs.
- Radar CW: Continuous wave radar measures Doppler shift (velocity) but cannot measure range without modulation.
CW Applications
- Component testing: Gain, loss, and compression measurements at a single frequency.
- Power calibration: CW power standards provide traceable references.
- Doppler radar: CW illumination measures target velocity from Doppler shift.
- Heating: Industrial and medical RF heating uses CW (microwave ovens are CW at 2.45 GHz).
Frequently Asked Questions
What does CW mean in RF?
CW means Continuous Wave, a constant-frequency, constant-amplitude sinusoidal signal with no modulation. CW signals are used as test stimuli for component characterization (gain, P1dB, IP3), as radar illumination for Doppler measurement, and as power calibration references.
Why is CW P1dB different from modulated P1dB?
CW P1dB is measured with a single constant-level tone. Modulated signals have varying instantaneous power (peaks above average). The peaks compress first, causing effective compression at lower average power than CW. OFDM signals with 10 dB PAPR compress at 10 dB lower average power than CW.
What is CW radar?
CW radar transmits a continuous wave and measures the Doppler frequency shift of returns to determine target velocity. It cannot measure range (no timing reference). CW radar is used for speed guns, motion detectors, and altimeters. FMCW adds frequency modulation to enable range measurement.