what is the wifi input baseband frequency

The Tx and Rx frequency of 802.11 b/g/n is either the 2.4 GHz band or the 5 GHz band.

From your question heading, I assume that you are not interested in the above, but rather the baseband characteristics?

In that case, then you must look at the bandwidth: 802.11 b/g support 20 MHz channels, while 802.11 n supports both 20 MHz and 40 MHz channels.