Transmission Frequency The NRP transmitter is continuously tunable over the range 5450 Mhz to 5825 Mhz Operational fixed frequency of 5625 Mhz is preferred Recall : c=nl Thus, 5625 MHz corresponds to a microwave wavelength of 5.33 cm (C band)

Weather Radar Bands The more common weather radar wavelengths and letter designations are:

Frequency The choice of frequency is important for a number of reasons: attenuation in precipitation is stronger at shorter wavelengths and is especially strong below 5cm the antenna size must scale with the wavelength to provide the same beamwidth: e.g. an antenna for an S band radar must be twice as big as for a C band

Pulse Repetition Frequency (PRF) The pulse repetition frequency (PRF) is the number of pulses emitted by the radar per second (pps) A pulse travelling to a target at range rmax and back will cover a distance 2rmax The pulse will make it back to the radar before the next pulse is emitted if: 2rmax=c/PRF

PRF and radar range rmax=c/2PRF Or…. rmax=c/2PRF Thus, the higher the PRF, the lower the effective range (ignoring second-trip echoes from objects located beyond rmax) But the lower the PRF the fewer samples the less reliable.

Rmax vs PRF

Rmax in selected modes We will see in a little while why we have to use higher PRF’s for Doppler