this option improves the phase noise performance from typically −135 dbc (1 hz) down to -139 dbc (1 hz) at 1 ghz carrier frequency, 20 khz offset. furthermore the nonharmonics are lower with this option (<- 90 dbc @ >10 khz carrier offset, 200 mhz < f ≤ 1500 mhz).
the option provides additionally the analog modulation types fm / φm.