What is the nature of the transmission and how does it affect the performance of the radar? There are a number of parameters which we can look at:

1. Power Output. Obviously, the power output of the different radars will differ from one another, but to give one an idea of the power required, navigation radars transmit somewhere in the vicinity of 30 KW. Compare this with the average cell phone that transmits approximately 2 watts. This is quite a considerable difference, but in order to obtain a reasonable range a large amount of output power is required. Most of the power is absorbed by the atmosphere and the fall-off with range is tremendous. Remember that only a portion of the signal that reaches an object is reflected and only a portion of that in the direction of the antenna.
2. Pulse length. The length of a pulse can vary anywhere between 0.05 micro seconds to 1.0 micro seconds. A typical radar will normally have two pulse lengths, one short and one long. The short pulse length will provide better range discrimination, ie if two targets lying on the same bearing but very close to each other in range, a short pulse length will display them as two separate contacts on the VDU. A long pulse length may display them as one contact. The long pulse provides greater range, whereas the short pulse will provide greater detail. A typical radar would normally have the ability to switch between two pulse lengths depending on the range chosen, ie short pulse length at short ranges (under 20 miles), long pulse at longer ranges (above 20 miles).
3. Pulse repetition frequency (PRF). When a radar transmits its radio signal, it transmits a series of pulses and not merely one. This could vary between 500 and 4000 pulses per second. The reason for this is to counteract the attenuation (weakening) of the signal by the atmosphere. The higher the PRF the greater the range of detection. The PRF together with the power output determine the range of the radar.
4. Antenna design. The projection of light from a car’s headlight or a torch usually takes the form of a circular cone of light. Whilst this is fine for determining one’s immediate environment, it would never do for a navigation radar. What is required is a beam which is very narrow in the horizontal plane (0.6° to 2°) and reasonably wide in the vertical plane (15° to 30°). This would provide a reasonably accurate bearing in azimuth whilst providing reasonable coverage in elevation, allowing for the pitching and rolling movement of the ship. The horizontal width of the beam has to be as narrow as possible since it decides the bearing discrimination of the radar, ie if two ships at the same range are very near to one another, a wide beam width would display a single echo on the VDU. A narrow beam width would show the two as separate echoes.