May I know why do we need the number 900 to make GSM900 meaningful?
> Is it because the rf signal is in 900 MHz? or the local oscillator
> used for GSM900 system is at 900 MHz? Kindly enlighthen.
GSM 900 is basically "shorthand" for the frequency used. It's the same way with GSM 1800, GSM 850 and GSM 1900. Different frequencies are used to transmit and receive. The frequencies are *around* those frequencies i.e. to say GSM 900 has different offsets for transmitting and receiving as do the other standards. Matter of fact for some odd reason it was decided that when GSM was overlayed on "cellular" frequencies in the US and Canada cellular was always called "800" (as opposed to PCS at 1900.) For some reason they decided to call GSM at cellular frequencies GSM 850. Reality is that it's the same band of frequency used for TDMA (IS-136) and CDMA (IS-95.)