Low-IF or direct upconversion transmitter

how can I quickly test, if I have a low-IF RF chip transmitter or a direct upconversion. It is a 2.4/5 GHz Wlan with differential IQ input ports in baseband.

The input baseband frequency should orientate in few hundred of MHz, fom 100-500MHz, the LO frequency is about 2.4GHz/5GHz, the resulting output at the tX would be the additional of this two frequency, the LO power would be in the range of -10dBm to 0dBm....

Rgds