calculating noise floor

how do we establish the xact value of noise floor in a certain area ( using spectrum analyser) & wat margin 2 keep from noise floor (dbm) for designin a front end TX module ?

i am goin to design a 2.4Ghz tx-rx front end module! so i require as 2 wat value of noise floor(dbm) to consider in my design!

Hi

You can simply measure noise floor of the requested frequency with the Spectrum Analyzer. Place the marker where you want and read the value, then the noise floor in dBm/Hz at that frequency will be:
Marker Value - 10 * log10(Resolution BW).

Regards

Be more specific, do you mean you want to measure the broadband noise leaking from the transmitter into the receiver front end bandwidth while they are both powered on?