Eglin AF NACs?

[AM909]

In the database, the USAF system 0x157 has a NAC of 140 for the Eglin sites 71-76. P25 systems mostly use NACs of the first two digits of the hex SID followed by the last digit of the site number, as does the rest of this system (NAC 15x). Can someone confirm the NAC for those Eglin sites (and provide the missing one for site 77)?

 

[GTR8000]

P25 systems mostly use NACs of the first two digits of the hex SID followed by the last digit of the site number, as does the rest of this system (NAC 15x).

The rule where the NAC uses the upper 8 bits of the 12 bit System ID applies primarily to Motorola ASTRO 25 systems, where the subscribers can validate the NAC against the System ID. Any other P25 systems following that pattern is a coincidence, not a rule.

As for the bottom 4 bits of the NAC being somehow related to the Site ID, that's simply untrue. Again, it's just a coincidence, not a rule. Plenty of ASTRO 25 systems that have a Site NAC that is unrelated to the Site ID.

 

[bravo14]

Is it possible nac 157 not 140?

 

[GTR8000]

Any NAC is possible, and if the sites follow the standard ASTRO 25 rule, they should be 15x. The only way to know for sure is to decode the sites to verify.

 

[bravo14]

Any NAC is possible, and if the sites follow the standard ASTRO 25 rule, they should be 15x. The only way to know for sure is to decode the sites to verify.

True. When I use to live 45 mints (east) from walton county I did see nac 157 at one time they were using 140.

 

[batdude]

these are my DSD logs from Eglin. I will submit a ticket and update as required:


Site: 1.71 NAC=157 ; Eglin AFB Main Base

Neighbor: BEE00.157-1.72 ; Eglin AFB Hurlburt Field
Neighbor: BEE00.157-1.73 ; Eglin AFB Floridale
Neighbor: BEE00.157-1.74 ; Eglin AFB Duke Field
Neighbor: BEE00.157-1.75 ; Eglin AFB Aux Field 2
Neighbor: BEE00.157-1.76 ; Eglin AFB Site B12
Neighbor: BEE00.157-1.77 ; Eglin AFB Site C52

Channel 4-401: 385.0125 CC
Channel 4-490: 386.125 SCC


Site: 1.72 NAC=157 ; Eglin AFB Hurlburt Field

Neighbor: BEE00.157-1.71 ; Eglin AFB Main Base
Neighbor: BEE00.157-1.73 ; Eglin AFB Floridale
Neighbor: BEE00.157-1.74 ; Eglin AFB Duke Field
Neighbor: BEE00.157-1.75 ; Eglin AFB Aux Field 2
Neighbor: BEE00.157-1.76 ; Eglin AFB Site B12
Neighbor: BEE00.157-1.77 ; Eglin AFB Site C52

Channel 4-405: 385.0625 CC
Channel 4-471: 385.8875 SCC


Site: 1.73 ; Eglin AFB Floridale

Channel 4-516: 386.45 CC


Site: 1.74 NAC=157 ; Eglin AFB Duke Field

Neighbor: BEE00.157-1.71 ; Eglin AFB Main Base
Neighbor: BEE00.157-1.72 ; Eglin AFB Hurlburt Field
Neighbor: BEE00.157-1.73 ; Eglin AFB Floridale
Neighbor: BEE00.157-1.75 ; Eglin AFB Aux Field 2
Neighbor: BEE00.157-1.76 ; Eglin AFB Site B12
Neighbor: BEE00.157-1.77 ; Eglin AFB Site C52

Channel 4-517: 386.4625 CC
Channel 4-557: 386.9625 SCC


Site: 1.75 NAC=157 ; Eglin AFB Aux Field 2

Neighbor: BEE00.157-1.71 ; Eglin AFB Main Base
Neighbor: BEE00.157-1.72 ; Eglin AFB Hurlburt Field
Neighbor: BEE00.157-1.73 ; Eglin AFB Floridale
Neighbor: BEE00.157-1.74 ; Eglin AFB Duke Field
Neighbor: BEE00.157-1.76 ; Eglin AFB Site B12
Neighbor: BEE00.157-1.77 ; Eglin AFB Site C52

Channel 4-514: 386.425 SCC
Channel 4-556: 386.95 CC


Site: 1.76 ; Eglin AFB Site B12

Channel 4-22: 380.275 CC


Site: 1.77 ; Eglin AFB Site C52

Channel 4-6: 380.075 CC



///////// RR dB has been updated with the above information ///////

Note: I made an assumption that sites 73, 76 and 77 all use the same site NAC as the other sites -- 157.

 

[GTR8000]

For educational purposes for those interested in the nitty-gritty details...ASTRO 25 systems (Motorola's brand of P25) will only allow a Site NAC to be set based on the upper 8 bits of the System ID (i.e. the first two characters), with the lower 4 bits of the Site NAC being 0-F. There is no requirement that the lower 4 bits have any relationship to the Site ID, or that the NAC be unique across sites within the same system/zone. Site 6 can have a NAC of 151, and every site within System 157 could be 151 NAC if desired. Traditionally, Motorola has synced up the Site NAC with the Site ID on most systems, but it's not a hard and fast rule, and there are plenty of exceptions out there.

Here is a representative screenshot from CSS showing how a site in System 157 might be setup. As you can see, the Access Code Index Requested has a range of 0-F HEX, and so when 1 is selected, that results in a NAC of 151. In other words, the choices of NAC are restricted to 150-15F, and thus a NAC of 140 would not be possible. Also note the "Color Code" field, which is for TDMA voice traffic channels. Yes, P25 TDMA channels use a Color Code as opposed to a NAC, so they're not exclusive to DMR.



And here is a screenshot from the CSS help file, explaining those fields.

 

[AM909]

"(based on NAC and 0x03F value)"

Do I understand correctly that it's saying the Color Code is the bottom 6 bits of the NAC?

I've been meaning to mention that DSD+FL, when decoding P2 voice channels, doesn't show NAC at all in the console log messages and shows the Color Code on the channel release messages, but it's the full 12-bit NAC of the site, not just the bottom 6 bits.

 

[GTR8000]

The TDMA Color Code is the bottom 6 bits of the NAC, correct.