NAC codes in P25 transmissions.
No you dont Only need nac which is like PL in analog world if you want to hear only certain users and not every user.
In the analog world, you could program the radio for carrier squelch operation, which would ignore the presence of CTCSS (i.e. Motorola calls it PL ), and get by.
The P25 world it is different, where there always is a NAC code being transmitted.
If you have a requirement to only hear a single site, then program in the NAC being used by that enity.
If you are not sure what their NAC code is, program $F7E, which is alike to programming your
analog radio for carrier squelch. The IMBE decoder then just passes audio reguardless of the actual NAC code. There are a few other wild card codes that are shown in the primer.
Daniels Radio Corp has a dandy P25 primer at:
Daniels Electronics - P25 Training Guide
B.