The receiver consists of a bank of filters, usually more than 100. The number of filters determines the maximum distance performance. Doubling the number of receiver filters increases distance performance by about 20%. Maximum distance performance is achieved when receiver filter size is equal to the maximum FM noise riding on the transmit signal. Reducing receiver filter size below average amount of FM transmit noise will not improve range performance. A CW radar is said to be matched when the receiver filter size matches the RMS bandwidth of the FM noise on the transmit signal. Types There are two types of continuous-wave radar: unmodulated continuous-wave and modulated continuous-wave. Unmodulated continuous-wave This kind of radar can cost less than $10 (2021). Return frequencies are shifted away from the transmitted frequency based on the Doppler effect when objects are moving. There is no way to evaluate distance. This type of radar is typically used with competition sports, like golf, tennis, baseball, NASCAR racing, and some smart-home appliances including light-bulbs and motion sensors. The Doppler frequency change depends on the speed of light in the air (c’ ≈ c/1.0003 is slightly slower than in vacuum) and v the speed of the target: The Doppler frequency is thus: Since the usual variation of targets' speed of a radar is much smaller than , it is possible to simplify with : Continuous-wave radar without frequency modulation (FM) only detects moving targets, as stationary targets (along the line of sight) will not cause a Doppler shift. Reflected signals from stationary and slow-moving objects are masked by the transmit signal, which overwhelms reflections from slow-moving objects during normal operation. Modulated continuous-wave Frequency-modulated continuous-wave radar (FM-CW) – also called continuous-wave frequency-modulated (CWFM) radar – is a short-range measuring radar set capable of determining distance. This increases reliability by providing distance measurement along with speed measurement, which is essential when there is more than one source of reflection arriving at the radar antenna. This kind of radar is often used as "radar altimeter" to measure the exact height during the landing procedure of aircraft. It is also used as early-warning radar, wave radar, and proximity sensors. Doppler shift is not always required for detection when FM is used. While early implementations, such as the APN-1 Radar Altimeter of the 1940s, were designed for short ranges, Over The Horizon Radars (OTHR) such as the Jindalee Operational Radar Network (JORN) are