Determining P25 channel frequencies

[kd7jfv]

Good morning, I'm trying to determine where additional sites are for this P25 system based on neighbor site lists from DSDplus Fastlane. Is there a way to determine what the frequency is for control channels, such as 0-174 or 0-20? This is for the Oregon Department of Corrections

2025/11/20 07:22:02 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.005-1.1; CC=0-174
2025/11/20 07:22:03 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.006-1.1; CC=0-20
2025/11/20 07:22:03 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.007-1.1; CC=0-370
2025/11/20 07:22:04 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.008-1.1; CC=0-370
2025/11/20 07:22:04 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.009-1.1; CC=0-400
2025/11/20 07:22:05 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.010-4.4; CC=0-310 854.8875 Oregon State Correctional Institution (OSCI)
2025/11/20 07:22:05 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.001-1.1; CC=0-108 852.3500 Deer Ridge Correctional Institution Deer Ridge Correctional Institution
2025/11/20 07:22:06 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.002-1.1; CC=0-108 Two Rivers Correctional Institution Two Rivers Correctional Institution
2025/11/20 07:22:06 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.003-1.1; CC=0-20
2025/11/20 07:22:07 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.004-1.1; CC=0-5

 

[DaveNF2G]

Try this table:

New FCC 800 MHz Channel Designations

 

[RMason]

Good morning, I'm trying to determine where additional sites are for this P25 system based on neighbor site lists from DSDplus Fastlane. Is there a way to determine what the frequency is for control channels, such as 0-174 or 0-20? This is for the Oregon Department of Corrections

The frequency can be calculated from the band plan:

Freq = (Spacing * Channel) + Base

It looks like there may be multiple band plans being used by different sites on this system with different base frequencies

Deer Ridge Correctional Institution​

CH ID	Type	Base (MHz)	Spacing (KHz)	Transmit Offset (MHz)
1	FDMA	851.00000	12.5	-45

Two Rivers Correctional Institution​

and​

Oregon State Correctional Institution (OSCI)​

CH ID	Type	Base (MHz)	Spacing (KHz)	Transmit Offset (MHz)
1	FDMA	851.01250	12.5	-45

So, there are multiple frequencies that are possible (0.0125Mhz apart) - depending on the band plan being used by the site:

Freq1 = (0.0125 * Channel) + 851.0000
Freq2 = (0.0125 * Channel) + 851.0125

Here are calculated values for both band plans:

Channel      Freq1       Freq2
0-5          851.0625    851.0750
0-20         851.2500    851.2625
0-108        852.3500    852.3625
0-174        853.1750    853.1875
0-310        854.8750    854.8875
0-370        855.6250    855.6375
0-400        856.0000    856.0125

You should be able to tune to both frequencies listed to locate the control channel.

 

[nd5y]

Try this table:

New FCC 800 MHz Channel Designations

That won't work. You need to know the band plan not FCC channels.

 

[wgbecks]

Good morning, I'm trying to determine where additional sites are for this P25 system based on neighbor site lists from DSDplus Fastlane. Is there a way to determine what the frequency is for control channels, such as 0-174 or 0-20? This is for the Oregon Department of Corrections

It appears your DSDPlus.sites file doesn't contain site data for the adjacent sites in question, else the site names and control channel frequencies would have appeared in the console display and logs. Also, the RRDB for Oregon Department of Corrections doesn't list any references to any of these unknown sites.

IE:
2025/11/20 07:22:02 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.005-1.1; CC=0-174
2025/11/20 07:22:03 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.006-1.1; CC=0-20
2025/11/20 07:22:03 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.007-1.1; CC=0-370
2025/11/20 07:22:04 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.008-1.1; CC=0-370
2025/11/20 07:22:04 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.009-1.1; CC=0-400

Therefore, to determine the frequencies, it will be necessary to obtain the systems band plan data from the log and compute
the unknown adjacent site control channel frequencies. To do this, open the log and capture the IDEN_UP and IDEN_UP_TDMA
messages. Sort them (Excel) and remove duplicates lines.

Here's what my local system looks like this after sorting and removing duplicates.

IDEN_UP ID=0 Base=851.00625 Offset=-45 Spacing=6.25 BW=12.5
IDEN_UP ID=1 Base=762.00625 Offset=+30 Spacing=6.25 BW=12.5
IDEN_UP_TDMA ID=2 Base=851.01250 Offset=-45 Spacing=12.5 BW=12.5 Slots=2
IDEN_UP_TDMA ID=3 Base=762.00625 Offset=+30 Spacing=12.5 BW=12.5 Slots=2


Look for the line containing ID=0 matching your log entries. Note the Base=(Frequency) and Spacing=values
whereby spacing is expressed in Kilohertz. IE: Spacing=6.25 = 0.006250 MHz. & Spacing=12.5 = 0.0125 Mhz.
Multiply the channel number for each of the unknown adjacent site frequencies by the spacing in Mhz then add that
to the Base frequency to obtain the actual control channel frequency.

 

[slicerwizard]

It appears your DSDPlus.sites file doesn't contain site data for the adjacent sites in question, else the site names and control channel frequencies would have appeared in the console display and logs. Also, the RRDB for Oregon Department of Corrections doesn't list any references to any of these unknown sites.

IE:
2025/11/20 07:22:02 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.005-1.1; CC=0-174
2025/11/20 07:22:03 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.006-1.1; CC=0-20
2025/11/20 07:22:03 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.007-1.1; CC=0-370
2025/11/20 07:22:04 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.008-1.1; CC=0-370
2025/11/20 07:22:04 Freq=854.162500 NAC=0A2 0000A.010-2.2 neighbor: Site 0000A.009-1.1; CC=0-400

The .sites file isn't relevant. DSD+ isn't displaying control channel frequencies because it doesn't know what bandplan data to use with those SysIDs.

Therefore, to determine the frequencies, it will be necessary to obtain the systems band plan data from the log and compute
the unknown adjacent site control channel frequencies. To do this, open the log and capture the IDEN_UP and IDEN_UP_TDMA
messages. Sort them (Excel) and remove duplicates lines.

Completely unnecessary since all of that data will be in the DSDPlus.P25data file under SysID 0000A.010

The .003/4/5/6/7/8/9 sites probably use the same bandplan as site .010, so just do the math using the base frequency and spacing values from SysID 0000A.101's bandplan #0 data. You'll likely get numbers similar to post #3 above.