# PSR Max Range Factors RNAV

There are many factors that affect the maximum range of a radar, and you should understand all of them. In increasing order of complexity, they are:

1. Power available. If the radar does not put enough power into the pulse, then it will not have the energy to get to the target and back.
2. Radar elevation. As radar is a space wave, and therefore line of sight, if the target is "over the hill" then the radar cannot reach it, even with unlimited power. This is the reason for the 1.23 x... equation.
3. The frequency of the wave. Do not get this confused with PRFPRF —Pulse Repetition Frequency, which is how often the radar pulses are sent out - this concept refers the the frequency of the wave in each of the pulses. The higher the frequency, the greater the degree of atmospheric attenuation. Therefore, if the frequency is higher then the maximum range will be lower (although there are benefits, such as increased clarity of return.)
4. Pulse repetition frequency (PRFPRF —Pulse Repetition Frequency). This is perhaps the hardest concept to understand. The radar dish can either be transmitting or receiving; not both. After it sends out a pulse, it listens for a period for the returns before transmitting the next pulse. However, if it transmits a second pulse before the return from the first pulse has returned, then it cannot know whether the return it has just received is from the first pulse or the second it has just transmitted. The return is therefore ambiguous. Therefore, if you want to have a long range radar, you have to "listen" for a longer period of time - which means you are not transmitting pulses as often — which means a lower PRFPRF —Pulse Repetition Frequency.

The formula for this is:

$\text{MTR} = 81000/\text{PRF}$

where $\text{MTR}$ MTRMTR —Maximum Theoretical Range is the Maximum Theoretical Range in nm, and $\text{PRF}$ is the Pulse Repetition Frequency in Hz.

Any or all of the 4 factors listed above could be the limiting factor on the maximum range of the radar.