Maintenance of a PAR.
*disclaimer* again, I worked on a different radar, but the theories still remain true.
Many of the parts in a radar have to be adjusted from time to time. These parts include various amplifiers of the signal. Amplifiers, as they continue to age, will start creeping in frequency. They also will not amplify as well. Both of these things, as you can imagine, are bad. If the signal to noise ratio on the receiver becomes to small then the radar will have a difficult time distinguishing between real returns, and the ambient noise generated in processing a signal. This is essentially how some jammers work. They simply try to overpower the return signals, and raise the noise floor. So, if the radar is not being properly maintained, it becomes a lead weight sucking huge amounts of energy.
So, there is a maintenance cycle created depending on the radar. The older ones will have more frequent maintenance cycles, this is mainly due to a lot of older tube technology in the amplifiers. Tubes are notorious for getting off frequency. The newer ones use more solid state technology, however, when it comes to creating large amounts of power, tubes is still where it's at. Nominally maintenance schedules will be set on a not-to-interfere basis, however, this isn't always the case.
