Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
you mean that you are using only an antenna but with 3 bands (GSM, DCS and GPS or the equivalent at USA). In this case first off all, use a realy good diplexter, you need low lost at GPS but a very big atenuation from GSM and DCS TX to the GPS RX. If your sistem is going to use thae GPS and GSM sistems at the same moment, yo have to garantee that the residual signal from your GSM TX in enough low to not asturate your GPS LNA, in other case you will louse GPS lock.
I hope I write abaut your problen and not only craisy things anfter a "oche de juerga" (party night)