How would one monitor radio IDs on the input frequencies?

[BinaryMode]

Did you enter them as OFT (assuming a Uniden)? I believe that's the only way to see RID's when monitoring conventionally.

I believe I have tried both, but I'll try again to make sure. Yes, a Uniden.

I'm intrigued what @buddrousa has done as well and may try that method too to see if there's a difference.

Then setup the scanner with as many 1 Frequency Trunking Systems as the System has Repeater Channels just use the Inputs
So if it has 5 Channels do not count the Control Channel so you setup 4 1 Frequency Trunking Systems.

 

[AB5ID]

Just wanted to throw this into the mix as food for thought. It comes from ChatGTP so take it for what it is worth.


You can determine the inbound (uplink) frequencies of a trunked APCO P25 system if you know the outbound (downlink) control channel and voice frequencies by using the standard frequency offsets for the system's band. These offsets vary based on the frequency band in which the system operates.

---

Step 1: Identify the System Band​

P25 trunked systems operate in several frequency bands, each with a standard uplink/downlink offset:

Band	Typical Downlink (Tower TX, Radio RX)	Typical Uplink (Radio TX, Tower RX)	Offset
VHF (150 MHz band)	159-162 MHz	152-155 MHz	~7-9 MHz
UHF (450-512 MHz band)	453-470 MHz	458-475 MHz	~5 MHz
700 MHz	769-775 MHz	799-805 MHz	30 MHz
800 MHz (Public Safety NPSPAC)	851-860 MHz	806-815 MHz	45 MHz
800 MHz (Rebanded & Non-NPSPAC)	851-869 MHz	806-824 MHz	45 MHz

---

Step 2: Apply the Offset​

If you have the downlink frequencies (control & voice), you can determine the uplink frequencies by subtracting the standard offset for the system's band.

Example: Determining Inbound Frequencies​

Let's say you are monitoring an 800 MHz P25 trunked system and you find these outbound (tower-to-radio) frequencies:

• Control Channel: 853.200 MHz
• Voice Channels: 854.100 MHz, 854.300 MHz, 854.500 MHz

To find the inbound (radio-to-tower) frequencies, subtract 45 MHz from each:

Outbound (Tower TX, Radio RX)	Inbound (Radio TX, Tower RX)
853.200 MHz (Control Channel)	808.200 MHz
854.100 MHz (Voice Channel 1)	809.100 MHz
854.300 MHz (Voice Channel 2)	809.300 MHz
854.500 MHz (Voice Channel 3)	809.500 MHz

So in this case, the radios would be transmitting on 808.200, 809.100, 809.300, and 809.500 MHz.

---

Step 3: Verify Using Radio Software or SDR​

If you want to confirm these frequencies:

1. Check FCC Databases – The FCC’s ULS (Universal Licensing System) can provide licensed trunking frequencies for a given area.
2. Use SDR (Software-Defined Radio) – A scanner or SDR (like an RTL-SDR, SDRplay, or Uniden scanner) can be tuned to possible uplink frequencies to listen for bursts of data or low-power radio transmissions from nearby units.
3. Trunking Decoders – Software like Unitrunker or DSDPlus can help decode the system and confirm inbound frequencies dynamically.

---

Key Takeaways​

• The inbound (uplink) frequencies are usually 45 MHz lower in 800 MHz systems and 30 MHz lower in 700 MHz systems.
• Other bands (VHF/UHF) use smaller offsets (~5-9 MHz).
• Once you have outbound control and voice frequencies, simply subtract the offset to find the inbound frequencies.
• Tools like SDR, trunking scanners, and FCC databases can help verify.

Would you like help identifying a specific system's frequencies in your area?

 

[KevinC]

Just wanted to throw this into the mix as food for thought. It comes from ChatGTP so take it for what it is worth.


You can determine the inbound (uplink) frequencies of a trunked APCO P25 system if you know the outbound (downlink) control channel and voice frequencies by using the standard frequency offsets for the system's band. These offsets vary based on the frequency band in which the system operates.

---

Step 1: Identify the System Band​

P25 trunked systems operate in several frequency bands, each with a standard uplink/downlink offset:

Band	Typical Downlink (Tower TX, Radio RX)	Typical Uplink (Radio TX, Tower RX)	Offset
VHF (150 MHz band)	159-162 MHz	152-155 MHz	~7-9 MHz
UHF (450-512 MHz band)	453-470 MHz	458-475 MHz	~5 MHz
700 MHz	769-775 MHz	799-805 MHz	30 MHz
800 MHz (Public Safety NPSPAC)	851-860 MHz	806-815 MHz	45 MHz
800 MHz (Rebanded & Non-NPSPAC)	851-869 MHz	806-824 MHz	45 MHz

---

Step 2: Apply the Offset​

If you have the downlink frequencies (control & voice), you can determine the uplink frequencies by subtracting the standard offset for the system's band.

Example: Determining Inbound Frequencies​

Let's say you are monitoring an 800 MHz P25 trunked system and you find these outbound (tower-to-radio) frequencies:

• Control Channel: 853.200 MHz
• Voice Channels: 854.100 MHz, 854.300 MHz, 854.500 MHz

To find the inbound (radio-to-tower) frequencies, subtract 45 MHz from each:

Outbound (Tower TX, Radio RX)	Inbound (Radio TX, Tower RX)
853.200 MHz (Control Channel)	808.200 MHz
854.100 MHz (Voice Channel 1)	809.100 MHz
854.300 MHz (Voice Channel 2)	809.300 MHz
854.500 MHz (Voice Channel 3)	809.500 MHz

So in this case, the radios would be transmitting on 808.200, 809.100, 809.300, and 809.500 MHz.

---

Step 3: Verify Using Radio Software or SDR​

If you want to confirm these frequencies:

1. Check FCC Databases – The FCC’s ULS (Universal Licensing System) can provide licensed trunking frequencies for a given area.
2. Use SDR (Software-Defined Radio) – A scanner or SDR (like an RTL-SDR, SDRplay, or Uniden scanner) can be tuned to possible uplink frequencies to listen for bursts of data or low-power radio transmissions from nearby units.
3. Trunking Decoders – Software like Unitrunker or DSDPlus can help decode the system and confirm inbound frequencies dynamically.

---

Key Takeaways​

• The inbound (uplink) frequencies are usually 45 MHz lower in 800 MHz systems and 30 MHz lower in 700 MHz systems.
• Other bands (VHF/UHF) use smaller offsets (~5-9 MHz).
• Once you have outbound control and voice frequencies, simply subtract the offset to find the inbound frequencies.
• Tools like SDR, trunking scanners, and FCC databases can help verify.

Would you like help identifying a specific system's frequencies in your area?

For VHF it's worth nothing unfortunately.

 

[AB5ID]

For VHF it's worth nothing unfortunately.

Why is it worth nothing? I'm not disagreeing with you just wanting to learn more

 

[nd5y]

For VHF it's worth nothing unfortunately.

Same for UHF.

 

[ecps92]

Why is it worth nothing? I'm not disagreeing with you just wanting to learn more

AI = Always Incorrect
in the US of A there is no band plan for input/outputs for Part 90 VHF

from what Tom added, AI is wrong
Some UHF = -5 (does not apply to the Broadcast "BA" allocations" which can be + or - and not always 5
UHF T = -3

 

[nd5y]

just wanting to learn more

AI is useless for anything but entertainment. Only a fool would use it for learning.
You want to know about uplink/input frequencies then read this:

Offset - The RadioReference Wiki

wiki.radioreference.com

and that article wasn't written by AI.

 

[AB5ID]

AI is useless for anything but entertainment. Only a fool would use it for learning.
You want to know about uplink/input frequencies then read this:

Offset - The RadioReference Wiki

wiki.radioreference.com

and that article wasn't written by AI.

Fair enough, I read through the Wiki; Thanks for the link.
Would you help me understand how I could figure out the input frequencies for this local non-simulcast trunk system, or is not possible to know with info available online?

Missouri Statewide Wireless Interoperable Network (MOSWIN) Site: Independence

Missouri Statewide Wireless Interoperable Network (MOSWIN) Site: Independence Details

www.radioreference.com

 

[KevinC]

Fair enough, I read through the Wiki; Thanks for the link.
Would you help me understand how I could figure out the input frequencies for this local non-simulcast trunk system, or is not possible to know with info available online?

Missouri Statewide Wireless Interoperable Network (MOSWIN) Site: Independence

Missouri Statewide Wireless Interoperable Network (MOSWIN) Site: Independence Details

www.radioreference.com

Systems the days use multi-block TSBK's, so the input frequency is transmitted in the VC grant. Look into one of the 9600 CC decoders as they should display the info.

 

[nd5y]

Would you help me understand how I could figure out the input frequencies for this local non-simulcast trunk system, or is not possible to know with info available online?

For VHF systems, even conventional repeaters, there is normally no standard offset and the FCC doesn't require specifying frequency pairs for each repeater.

There could be 6 repeaters and the license will show 6 FB frequencies (outputs) and 6 MO and/or FX frequencies (inputs). Normally there is no way to tell which input is paired with which output. You might get lucky and find that the number order of the frequencies on the license matches if the person who filled out the application entered all the data in order.

Here is the license for the site you posted.

FCC Callsign WQPV891 (MISSOURI, STATE OF)

FCC Callsign WQPV891 (MISSOURI, STATE OF)

www.radioreference.com

MOSWIN uses a mix of public safety, paging, auctioned marine and federal frequencies depending on the site.
The paging and marine channels, which this site doesn't have, are paired so those are easy to figure out.
The only thing you can tell in this case is 151.34 is the input to 154.935.
The 163-172 MHz frequencies are federal. All you can tell from the license is 163-166 MHz FX1 and MO8 are inputs and 169-172 MHz FB8 are outputs. There is no way to tell how they are paired without direct monitoring.

 

[AB5ID]

For VHF systems, even conventional repeaters, there is normally no standard offset and the FCC doesn't require specifying frequency pairs for each repeater.

There could be 6 repeaters and the license will show 6 FB frequencies (outputs) and 6 MO and/or FX frequencies (inputs). Normally there is no way to tell which input is paired with which output. You might get lucky and find that the number order of the frequencies on the license matches if the person who filled out the application entered all the data in order.

Here is the license for the site you posted.

FCC Callsign WQPV891 (MISSOURI, STATE OF)

FCC Callsign WQPV891 (MISSOURI, STATE OF)

www.radioreference.com

MOSWIN uses a mix of public safety, paging, auctioned marine and federal frequencies depending on the site.
The paging and marine channels, which this site doesn't have, are paired so those are easy to figure out.
The only thing you can tell in this case is 151.34 is the input to 154.935.
The 163-172 MHz frequencies are federal. All you can tell from the license is 163-166 MHz FX1 and MO8 are inputs and 169-172 MHz FB8 are outputs. There is no way to tell how they are paired without direct monitoring.

Thank you. I really appreciate your time and the explanation. My head started spinning trying to understand VHF/UHF part of the Motorola trunking section on the Wiki page.
Many thanks!
Steve

 

[AB5ID]

Systems the days use multi-block TSBK's, so the input frequency is transmitted in the VC grant. Look into one of the 9600 CC decoders as they should display the info.

Thank you. Do you know if Pro96com still a viable option? I have a 396xt with serial cable that I'm not using.

 

[KevinC]

Thank you. Do you know if Pro96com still a viable option? I have a 396xt with serial cable that I'm not using.

I would think so. You may have to dig around to find the VC grant messages, I haven’t used it in several years and don’t recall the option to see them.

 

[nd5y]

There could be 6 repeaters and the license will show 6 FB frequencies (outputs) and 6 MO and/or FX frequencies (inputs). Normally there is no way to tell which input is paired with which output.

This assumes that all the repeaters are in the same location. Usually the location for mobiles is a radius around the repeater or base. If there are multiple locations with only one repeater per location then you can usually match the inputs with the repeaters.

Sometimes the mobile location is a state, county or other area and you won't be able to match them if there is more than one repeater.