How if find Setting Band Plan for Trunking VHF
- Thread starter BorisG
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slicerwizard
Member
Easiest route would be to get an inexpensive DVB-T (RTL2832U variety) dongle and feed the control channel audio to a decoder program like TRUNK88 or Unitrunker. That will give you the voice channel numbers. When combined with the actual frequencies that the voice channels use, the bandplan values can be easily calculated.
Most Motorola systems for VHF/UHF have an offset of 380.
The formula is simple enough. For a channel number "C", base frequency "B", channel number offset "O", and channel step size "S" (also called channel spacing), the formula for the channel frequency F is ...
F = B + S * (C - O)
Here's an example:
Federal Detention Center Houston Trunking System, Houston, Texas - Scanner Frequencies
Base 407.00000 Mhz
Spacing 12.5 Khz
Offset 380
The above site has control channels 407.41250, 408.45000, 409.41250, 410.21250.
The channel number for 407.4125 is 413.
The channel number for 410.2125 is 637.
Given just this limited information, you can calculate the step size.
S = (F2 - F1) / (C2 - C1)
(410.2125 - 407.4125) / (637 - 413) = 2.800 / 224 = 12.5 khz.
Given a channel step of 12.5 khz and an offset of 380,
F = B + S * (C - O) = B + 12.5 khz * (413 - 380) = B + 12.5 khz * 33 = 412.5khz.
We know the frequency for channel number 413 is 407.4125 Mhz so ...
407.4125 Mhz = B + 0.4125 Mhz
Algebra tells us ...
B = 407.4125 Mhz - 0.4125 Mhz = 407 Mhz
You can work this all out in a few minutes in a spreadsheet like Calc or Excel.
Life gets a bit more complicated when the site uses more than band plan one entry.
The formula is simple enough. For a channel number "C", base frequency "B", channel number offset "O", and channel step size "S" (also called channel spacing), the formula for the channel frequency F is ...
F = B + S * (C - O)
Here's an example:
Federal Detention Center Houston Trunking System, Houston, Texas - Scanner Frequencies
Base 407.00000 Mhz
Spacing 12.5 Khz
Offset 380
The above site has control channels 407.41250, 408.45000, 409.41250, 410.21250.
The channel number for 407.4125 is 413.
The channel number for 410.2125 is 637.
Given just this limited information, you can calculate the step size.
S = (F2 - F1) / (C2 - C1)
(410.2125 - 407.4125) / (637 - 413) = 2.800 / 224 = 12.5 khz.
Given a channel step of 12.5 khz and an offset of 380,
F = B + S * (C - O) = B + 12.5 khz * (413 - 380) = B + 12.5 khz * 33 = 412.5khz.
We know the frequency for channel number 413 is 407.4125 Mhz so ...
407.4125 Mhz = B + 0.4125 Mhz
Algebra tells us ...
B = 407.4125 Mhz - 0.4125 Mhz = 407 Mhz
You can work this all out in a few minutes in a spreadsheet like Calc or Excel.
Life gets a bit more complicated when the site uses more than band plan one entry.
Spitfire8520
I might be completely clueless! =)
I know there's already a post above this, but I figure I might as well post this anyways.
You should actually be able to use the BCD396XT directly with Unitrunker if you have some type of interface cable. This should easily allow you to find the channel numbers you need to calculate everything else.
Determining Base/Step/Offset for VHF/UHF Motorola Systems - The RadioReference Wiki
Ideally, the Base Frequency that you're interested in is Channel 380 (Hex: 17C). Channels 0-379 are all input frequencies and therefore not useful for scanning. This will most likely mean that your Offset will be 380 as well since we doesn't care about 0-379.
Therefore:
Voice_Freq = Base_Freq + ( (Channel# - 380) x Step )
So Channel 383 is calculated as:
Voice_Freq = Base_Freq + ( 3 x Step )
To calculate the Step, you need to know 2 of the frequencies being used and the channel numbers for those frequencies, which is provided by programs noted above.
Once you have the frequencies, you have to do the math shown in the above link. I'm going to use US Federal example because I have the numbers right in front of me, but the process will be exactly the same for any frequency you come across. Note that most scanners use Step in kHz, so you will need to convert.
For example:
Now to calculate the Base Frequency, we can reorder the above equation using algebra:
Base_Freq = Voice_Freq - ( (Channel# - 380) x Step )
Just simply choose one of the frequency/channel numbers you know and run it through the calculation since you know 3 of the variables:
Now I have a Base Frequency, Spacing, and Offset. Taking a quick look at the BCD396XT, you will need to find the upper base frequency. Uniden has provided a Excel Spreadsheet for finding that.
You should actually be able to use the BCD396XT directly with Unitrunker if you have some type of interface cable. This should easily allow you to find the channel numbers you need to calculate everything else.
Determining Base/Step/Offset for VHF/UHF Motorola Systems - The RadioReference Wiki
Ideally, the Base Frequency that you're interested in is Channel 380 (Hex: 17C). Channels 0-379 are all input frequencies and therefore not useful for scanning. This will most likely mean that your Offset will be 380 as well since we doesn't care about 0-379.
Therefore:
Voice_Freq = Base_Freq + ( (Channel# - 380) x Step )
So Channel 383 is calculated as:
Voice_Freq = Base_Freq + ( 3 x Step )
To calculate the Step, you need to know 2 of the frequencies being used and the channel numbers for those frequencies, which is provided by programs noted above.
Once you have the frequencies, you have to do the math shown in the above link. I'm going to use US Federal example because I have the numbers right in front of me, but the process will be exactly the same for any frequency you come across. Note that most scanners use Step in kHz, so you will need to convert.
For example:
Code:
Frequency 1 = 406.7750 MHz, Channel 442
Frequency 2 = 407.1250 MHz, Channel 470
Step (in MHz) = (407.1250 - 406.7750) / (470 - 442)
= 0.35 / 28
= 0.0125 MHz
Step (in kHz) = 1000 x 0.0125
= 12.5 kHzNow to calculate the Base Frequency, we can reorder the above equation using algebra:
Base_Freq = Voice_Freq - ( (Channel# - 380) x Step )
Just simply choose one of the frequency/channel numbers you know and run it through the calculation since you know 3 of the variables:
Code:
Voice_Freq = 406.7750 MHz, Channel 442
Step = 0.0125 MHz
Base_Freq = 406.7750 - ( (442 - 380) x 0.0125) )
= 406.7750 - ( 62 x 0.0125 )
= 406.7750 - 0.775
= 406.0000 MHzNow I have a Base Frequency, Spacing, and Offset. Taking a quick look at the BCD396XT, you will need to find the upper base frequency. Uniden has provided a Excel Spreadsheet for finding that.
I collected the data
Can someone please help me what settings I need?
What do I have to fill in the software ? (table BandPlan Setting)
What i need to Select?
Frequency listen:
169.090
169.150
170.040
169.035
168.990
...
Frequency Control:
169.7125
169.7375
169.8625
...
Video From scanner Custom search:
https://www.youtube.com/watch?v=aKv5asSeuO0
Can someone please help me what settings I need?
What do I have to fill in the software ? (table BandPlan Setting)
What i need to Select?
Frequency listen:
169.090
169.150
170.040
169.035
168.990
...
Frequency Control:
169.7125
169.7375
169.8625
...
Video From scanner Custom search:
https://www.youtube.com/watch?v=aKv5asSeuO0
Go back and read Post #3.
Looks good Boris!
We can use the control channel as a reference for guessing a band plan. However, we need a second frequency to confirm the step size.
Here's are two guesses - one for step size 12.5 khz and another for step size 5 khz.
Lo LCN is 380
Hi LCN is 760
Base frequency depends on step size.
167.9825 Mhz for a step size of 5 khz.
165.3875 Mhz for a step size of 12.5 khz.
It could be a different step size and base frequency.
We can use the control channel as a reference for guessing a band plan. However, we need a second frequency to confirm the step size.
Here's are two guesses - one for step size 12.5 khz and another for step size 5 khz.
Lo LCN is 380
Hi LCN is 760
Base frequency depends on step size.
167.9825 Mhz for a step size of 5 khz.
165.3875 Mhz for a step size of 12.5 khz.
It could be a different step size and base frequency.
Hi Boris!
Don't give up.
The other control channel is for a different site. We need to know two channels on the same site. To know two channels is to know the channel number and frequency.
Right now we know one channel on site 31 and another channel on site 35.
For these frequencies ...
What is the channel number for each frequency?
If site 31 and site 35 use the same band plan, it likely needs two or more band plan entries since 146 Mhz and 169 Mhz are too far apart.
Assuming the sites all share the same band plan, try this.
Find as many peer site control channel frequencies as possible. Search for other control channels belonging to 3D3D. We may be able to build a band plan from this list of neighboring sites' control channels.
Don't give up.
The other control channel is for a different site. We need to know two channels on the same site. To know two channels is to know the channel number and frequency.
Right now we know one channel on site 31 and another channel on site 35.
For these frequencies ...
What is the channel number for each frequency?
If site 31 and site 35 use the same band plan, it likely needs two or more band plan entries since 146 Mhz and 169 Mhz are too far apart.
Assuming the sites all share the same band plan, try this.
Find as many peer site control channel frequencies as possible. Search for other control channels belonging to 3D3D. We may be able to build a band plan from this list of neighboring sites' control channels.
talkpair
Member
From the information provided thus far, I have only been able to find 3 patterns myself. All of which I do not feel are correct.
Unitrunker reports 7 active voice channels, yet I see only 5 frequencies.
Are you confident that the frequencies you provided are from the same site the Unitrunker report was ran on, and not an adjacent site?
Is it possible that some of the voice frequencies might be slightly different than the ones you provided? In other words, is it possible that 168.99 is really 168.9875?
Unitrunker reports 7 active voice channels, yet I see only 5 frequencies.
Are you confident that the frequencies you provided are from the same site the Unitrunker report was ran on, and not an adjacent site?
Is it possible that some of the voice frequencies might be slightly different than the ones you provided? In other words, is it possible that 168.99 is really 168.9875?
nd5y
Member
If you switch sites while Unitrunker is running sometimes it creates fake sites or channels.
Spitfire8520
I might be completely clueless! =)
Having a multiple scanner or a multiple RTL-SDR setup would be very helpful in trying to figure out the band. Having a second receiver would allow you to listen to a frequency and match to a channel (LCN) on Unitrunker when you see it active.
Right now, it sounds like you have overlap of multiple sites. This makes it more complicated since the frequencies you have posted might belong to different sites then what we have seen so far.
Basically, you need to figure out what Frequency equals what LCN. If you don't have a 2nd receiver, find more sites/control channels and post their LCN Frequency pair as mentioned previously.
Right now, it sounds like you have overlap of multiple sites. This makes it more complicated since the frequencies you have posted might belong to different sites then what we have seen so far.
Basically, you need to figure out what Frequency equals what LCN. If you don't have a 2nd receiver, find more sites/control channels and post their LCN Frequency pair as mentioned previously.
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