Watton925,
I just looked at the SIRN system and it's a standard P25 Phase-I SmartZone system. Each site (RFSS) will have it's own primary and alternate control and voice trunk channels. You'll find the frequencies assigned to each of the sites part of a pool that are periodically reused throughout the system in accordance with engineering practice designed to maximize frequency reuse with a minimum of interference potential between sites.
It's also common practice to assign different NAC's among cochannel (same frequency) sites that plays a key role in the operation
of the subscribers units (SU's) ability to qualify control channel messages and voice trunk traffic that might be originating from a another site within the same system or from a from a foreign system on the same frequency, and where System ID and WACN also play an important role
in this regard.
Now back to your original post. There's no need to
simultaneously monitor multiple control channels unless you have a need for multiple receivers set to scan specific talkgroups home to those sites and that you can actually receive said sites form your particular location with requisite equipment to do so.
All that is necessary for a single receiver per site is to ensure the primary and alternate control channels (frequencies) are listed in your trunk.tsv file along with the correct NAC for that site. Alternatively, boatbod's version of op25 provides for the ability to set the NAC to 0x0 that will tell rx.py to use the first NAC is sees when searching the list of control channel frequencies populated in your trunk.tsv file. This capability is very helpful when initially setting up op25 for when you may now know the NAC or are uncertain of what it is.
Another unique application of the 0x0 NAC feature is that it gives one the ability to setup a device like a Raspberry PI for portable or mobile applications where you only need to populate a comma separated list of control channels in your trunk.tsv file and whereby setting the 0x0 NAC to will maintain decoding of system control channels as you roam about regardless of the NAC employed at any given site that you may be in range to receive.
Thank you
@boatbod for this very useful and wonderful feature!
Bill