I'm trying to figure out the bandplan for a system. I use Unitrunker to log all info I hear on trunked systems.
In order for me to properly figure out the band plan, I need to NOT have a bandplan set up in Unitrunker initially, right? What I mean is that when I first come upon a control channel for a new system, I want to log that channel ID. Then I want to wait and watch for traffic and see what other channel IDs pop up. Then I want to figure out the other frequencies based upon the channel IDs I found. Then once I have channel IDs and frequencies, I want to then, and only then, figure out the proper base/offset/spacing values for the bandplan. Is this correct?
For instance, I found a control channel for a new system. That channel was 410.400 (reported channel ID 759 in Unitrunker). Then the next day I found the same system using a different control channel - 408.25 (reported channel ID 587 in Unitrunker).
Then on the third day I found the same system using 408.8125 control channel but failed to log the channel ID.
At this point I do have enough information to figure out the base/offset/spacing, yes?
Here is how I figured it:
#587 408.250 alt cc
# 408.8125 alt cc
#759 410.400 cc
OFFSET = 380
F1 = 408.25
F2 = 410.400
CID1 = 587
CID2 = 759
STEP = 1000 x (F1 - F2) / (CID1 - CID2) =
= 1000 x (408.25 - 410.40) / (587-759) =
= 1000 x (-2.15) / (-172) =
= 1000 x (2.15 / 172) =
= 1000 x .0125 =
= 12.5 khz
BASE = F1 - ((CID1-OFFSET) x (STEP / 1000) =
BASE = 408.25 - ((587-380) x .0125) =
BASE = 408.25 - 2.5875 =
BASE = 405.6625
The problem with this is that I cannot add 405.6625 into my BCD396T as the base frequency because it tells me that frequency is out of band. I have the system set up as a Moto Type II UHF.
So then I started playing around in Unitrunker with the Insert Bandplan and came up with a combination that seemed to jive. That was:
Base: 406 (originally thought it was 405.6625)
Offset: 407 (originally thought it was 380)
Step: 12.5 kHz
BUT, then Gilligan pointed me to this system which is similar: http://radioreference.com/modules.php?name=RR&sid=3519
In this system it has three of the frequencies that I know are in my system (they are definitely different systems, I'm in Ohio). So I look at the base/offset/spacing and they don't jive with my base/offset - only the spacing is the same. And when I use the base/offset that is listed in this system as a baseline when creating a bandplan in Unitrunker for the system I'm monitoring, none of the channel IDs jive.
So I'm wondering where I went wrong and what information is right. Is it 405.6625/380/12.5 or 406/407/12.5 or should it be the same as the system that Gilligan referenced, OR should it be something else?
Thanks
Mike
In order for me to properly figure out the band plan, I need to NOT have a bandplan set up in Unitrunker initially, right? What I mean is that when I first come upon a control channel for a new system, I want to log that channel ID. Then I want to wait and watch for traffic and see what other channel IDs pop up. Then I want to figure out the other frequencies based upon the channel IDs I found. Then once I have channel IDs and frequencies, I want to then, and only then, figure out the proper base/offset/spacing values for the bandplan. Is this correct?
For instance, I found a control channel for a new system. That channel was 410.400 (reported channel ID 759 in Unitrunker). Then the next day I found the same system using a different control channel - 408.25 (reported channel ID 587 in Unitrunker).
Then on the third day I found the same system using 408.8125 control channel but failed to log the channel ID.
At this point I do have enough information to figure out the base/offset/spacing, yes?
Here is how I figured it:
#587 408.250 alt cc
# 408.8125 alt cc
#759 410.400 cc
OFFSET = 380
F1 = 408.25
F2 = 410.400
CID1 = 587
CID2 = 759
STEP = 1000 x (F1 - F2) / (CID1 - CID2) =
= 1000 x (408.25 - 410.40) / (587-759) =
= 1000 x (-2.15) / (-172) =
= 1000 x (2.15 / 172) =
= 1000 x .0125 =
= 12.5 khz
BASE = F1 - ((CID1-OFFSET) x (STEP / 1000) =
BASE = 408.25 - ((587-380) x .0125) =
BASE = 408.25 - 2.5875 =
BASE = 405.6625
The problem with this is that I cannot add 405.6625 into my BCD396T as the base frequency because it tells me that frequency is out of band. I have the system set up as a Moto Type II UHF.
So then I started playing around in Unitrunker with the Insert Bandplan and came up with a combination that seemed to jive. That was:
Base: 406 (originally thought it was 405.6625)
Offset: 407 (originally thought it was 380)
Step: 12.5 kHz
BUT, then Gilligan pointed me to this system which is similar: http://radioreference.com/modules.php?name=RR&sid=3519
In this system it has three of the frequencies that I know are in my system (they are definitely different systems, I'm in Ohio). So I look at the base/offset/spacing and they don't jive with my base/offset - only the spacing is the same. And when I use the base/offset that is listed in this system as a baseline when creating a bandplan in Unitrunker for the system I'm monitoring, none of the channel IDs jive.
So I'm wondering where I went wrong and what information is right. Is it 405.6625/380/12.5 or 406/407/12.5 or should it be the same as the system that Gilligan referenced, OR should it be something else?
Thanks
Mike
