Finding trunked P25 channel frequencies, (not cc)

[hhca]

Hi, Im trying to find out how many calls a system can have at once, so figured i can just look at how many fdma channel frequencies a system has/uses (and x2 if it phase 2 tdma). Now i can monitor the system and just write them down, but you wont know if there are some spare that are not commonly used but might be when higher traffic.

Im using sdr based tuning with linux and windows. In sdrtrunk it does output the following data but i cant seem to correlate it to the active channels i find it uses. Maybe there is better software for getting these details? or maybe its just not available. As even a neigbour site well within range of this one shows the same frequency band plan, so it must internally know what channel frequencies to use differently to the one below to avoid conflict.

Activity Summary - Decoder:P25 Normal (C4FM)

Network
  NAC:xxx WACN:xxxx SYSTEM:xxx LRA:0

Current Site
  SYSTEM:xxx SITE:xx RF SUBSYSTEM:3 LOCATION REGISTRATION AREA:0  STATUS:ACTIVE RFSS NETWORK CONNECTION
  PRI CONTROL CHANNEL:4-1162 DOWNLINK:xxx UPLINK:xxx
  SEC CONTROL CHANNEL:4-1082 DOWNLINK:xxx UPLINK:xxx
  CURRENT DATA CHANNEL:15-4095 DOWNLINK:0 UPLINK:0

Neighbor Sites
xxx

Frequency Bands
  BAND:0 FDMA BASE:851006250 BANDWIDTH:12500 SPACING:6250 TRANSMIT OFFSET:-45000000
  BAND:1 FDMA BASE:762006250 BANDWIDTH:12500 SPACING:6250 TRANSMIT OFFSET:30000000
  BAND:2 TDMA BASE:851012500 BANDWIDTH:12500 SPACING:12500 TRANSMIT OFFSET:-900000000 TIMESLOTS:2
  BAND:3 TDMA BASE:762006250 BANDWIDTH:12500 SPACING:12500 TRANSMIT OFFSET:600000000 TIMESLOTS:2
  BAND:4 FDMA BASE:412475000 BANDWIDTH:12500 SPACING:6250 TRANSMIT OFFSET:-9450000
  BAND:5 FDMA BASE:420000000 BANDWIDTH:12500 SPACING:6250 TRANSMIT OFFSET:5200000
  BAND:6 TDMA BASE:412475000 BANDWIDTH:12500 SPACING:12500 TRANSMIT OFFSET:-189000000 TIMESLOTS:2
  BAND:7 TDMA BASE:420000000 BANDWIDTH:12500 SPACING:12500 TRANSMIT OFFSET:104000000 TIMESLOTS:2
  BAND:8 FDMA BASE:467512500 BANDWIDTH:12500 SPACING:12500 TRANSMIT OFFSET:-10000000
  BAND:9 TDMA BASE:467512500 BANDWIDTH:12500 SPACING:12500 TRANSMIT OFFSET:-200000000 TIMESLOTS:2

 

[GTR8000]

An actual list of site channels is not available over the air. You simply have to monitor the system 24/7 to eventually determine all of the frequencies.

Even in the U.S. where the FCC licenses are readily available, there's no guarantee that a) all frequencies are actually correlated to a physical repeater or b) the license is accurate. I know of systems that were "over-licensed" and some of the frequencies were not and will never be used, yet they remain on the license. And of course systems that are using unlicensed frequencies. In fact, I know of both of those being true for a single two-site system...go figure.

 

[GTR8000]

Oh and as far as the band plan (labeled Frequency Bands in SDRTrunk), that is simply the table that the subscribers use to know what traffic channel frequencies to tune to. The system sends a channel # over the air, and the band plan is used by the subscribers to calculate the actual frequency by using the base frequency, offset, and spacing values.

 

[hhca]

Ah thanks for that, I understand what it means now. Yes we too here in australia have licenses online but can be a bit tricky to know which ones are associated with which control on a big site.

 

[Kazzaw]

From what I've seen, most stick in line with what is issued on the ACMA database in my local area anyway.

I've been able to match most frequencies with their respective sites without too many issues (although there are a couple odd ones)

 

[WA0CBW]

One thing for sure if the FCC pays them a visit they better be right with what the license says.
BB

 

[hhca]

In australia id guess 99% of trunked systems are run by the government so im guessing they generally match the acma registrations. so @Kazzaw how do you match them up ? i guess just look at registrations with 10K1F9W, Omni, Transmit, and NSW TELCO , 2 of which will be your pri/sec controls and the rest trunk channels

 

[Kazzaw]

Excel spreadsheet with conditional formatting - I've since given up on it though, programming either a scanner or software only requires the CC info.

If you don't already have access to a google sheets spreadsheet with the listing of CC's, shoot me a message and I can point you in the right direction