Spectral environment estimation systems and methods are provided for use with frequency hopped communications systems. It is proposed that the terminal caps have detachable fixing means that engage in the top strip of the wiper strip, wherein the axial movability of the resilient rails relative to the wiper strip is limited by the terminal caps. The selected epoch may be a second, minute, hour, week, month, year, or so forth. The apparatus also includes a controller arranged to obtain the non-contact measurement and to use the non-contact measurement to control the cooling provided by the first array.