Return Loss is valuated by VSWR(Voltage Stationary Wave Ratio). Usually GSM feeders are adapted to 50 Ohms. Of course that this perfect adaptation can be matched for a narrow number of channels and not for full GSM bandiwth of 124 channels.VSWR value is the worst value inside all bandwith. usuually a value within (1.3-1.5) dB is accepted.
Cable loss is due to distance attenuation and is given per 100 m. Some feeders have 10dB/100m attenuation others have 2.5 dB/100m
Site analyser(site master) is a specific tool that allow you to measure all staffs regarding antenna and feeder system.It injects a signal in feeder system( including connectors, feeders, jumpers, antennas ,TMA and REKs) and it measures the VSWR attenuation etc….
Hope I gave you a clue:)Mail me if there are more to be detailed