You can use SmartRF Studio to capture the packet.
1) Select the 38.4 kbps Typical Settings as a starting point. Change Symbol rate and Deviation
2) Use the "Packet RF" option. Tick off "advanced" and set the Length Configuration to fixed. Set the length to 20 (say) as you do not know the packet length
3) Not sure what sync word length is being used by CC1020. Assume 4 bytes: 0xD391D391. Set CC1120 SYNC3,2,1,0 = 0xD391D391. You might also check with 2 bytes but then you need to change SYNC_CFG0[4:2] to 2
4) Press RX button. The transmitted packet should then be received. Note that the CRC will be wrong as the packet length is most likely not 20 bytes (say) and you do not know if a CRC byte is actually being transmitted by CC1020. The same packet should be received each time.
RX bandwidth is the on-chip filter BW and needs to be wide enough to fit the transmitted signal. 100 kHz BW for 19.2 kbps and +/-9.9 kHz deviation is more than enough.