Batboard

OK- A question for the gurus-

It is my understanding that 800MHz trunking systems steer the subscriber radios to their assigned voice channels using a standardized band channel numbering plan.

It is also my understanding that VHF / UHF OBT systems specify the voice channel assignment by specifying a number of steps, of a given step size, up from an arbitrary base frequency, since there is no standardized numbering scheme.

Now the question- In OBT, the frequency ranges can be split into several steps. Does the system identify the voice channels by counting continuously up from the bottom of the lowest range, and including the appropriate gaps, or does it handle each range individually?

For example, if the first frequency range was 200 steps wide, and the second was 100 steps, and the system wanted to assign a voice channel that worked out as the fifth step in the second range would it: a) Tell the subscriber unit to go to step 205 (counting from the bottom, and making the upper value of range 1 a critical number), or 2) Tell the subscriber unit to go to Range 2, Step 5?

Thanks!

It's a combination of Site Controller programming, and radio programming. Basically, when you order the system, you have to tell Motorola all the frequencies in the system (of course), and what size steps you want the controller tell the radio to make (25KHz, 50KHz, 12.5KHz, etc). Let's assume you choose 25KHz as the step size. The lowest frequency is considered the "base" frequency which you have to program into the field radios. If the next frequency up is say 200KHz from the base, the controller will tell the radio to go 8 steps to work on that frequency. If the next one up is 100Khz higher (300KHz away from base frequency) then it is directed to go 12 steps from base. That's it in a nutshell.

Todd

Thanks for the reply.

What I am actually trying to sort out is how the system / radios handle the split frequency ranges. It appears that you are only allowed to have a maximum of 380 steps between all three ranges, so I was trying to sort out how it counted channels across ranges.

For example, say you have a system where your frequency ranges (on the TX side) fall between:
Range 1: 460.000 - 461.100
Range 2: 465.000 - 466.000
Range 3: 470.000 - 471.000

If the controller wanted to assign a voice channel on 470.500 would it 1) Tell the radio "Go X steps up from the Range 1 base" counting continuously through the ranges, with the upper frequency of range 1 and lowest frequency of range 2 as adjacent step numbers, or would it 2) just say "Go X steps up from the Range 3 base"?

I had assumed (dangerous habit), given the channel count limitation, that the system counts continuously, and that an error in the upper frequency of the lower most range would throw the whole system off, since the upper range channels would all be off as a result in the error at the top of the lower range.

However, I recently saw a system on RR that had 380 steps in the first range alone, and 500+ in the second. I punched the system into the old BC780, and it seemed to track it fine, which seemed to challenge my previous assumption.

Also, while I'm at it, how does an OBT system do AMSS or SmartZone? It seems as if the need for the specific frequency ranges would make it difficult to define multiple sites within a system. Again, I am obviously missing something, because it can clearly be done.

HumHead wrote:Now the question- In OBT, the frequency ranges can be split into several steps. Does the system identify the voice channels by counting continuously up from the bottom of the lowest range, and including the appropriate gaps, or does it handle each range individually?

It counts continuously up. If the first range has 120 channels, the second has 90, and the third 170 then the system would send out 380 - 499 for the first range, 500 - 589 for the second, and 590 - 759 for the third.

The RSS/CPS will make sure all ranges equal 380 available channels. This spreadsheet may help out in understanding the assignment calculations.