PRO-96 Custom Table?

[bwigg]

I am curious as to what function each parameter has that is entered into PRO-96 custom tables. I assume the channel number is the FCC numbers for the relevant freqs. I haven't found any info that describes exactly how this custom table works.

 

[DonS]

I am curious as to what function each parameter has that is entered into PRO-96 custom tables. I assume the channel number is the FCC numbers for the relevant freqs. I haven't found any info that describes exactly how this custom table works.

No, the channel number has nothing to do with the FCC. The channel number is based solely on the channel number sent by the Mot trunking system on the CC.

Here's how the custom table works...
1. the scanner receives a "call grant" or "call update" message on the CC
2. the message contains (in relevant part) a talkgroup ID and a channel number
3. the scanner uses the channel number to calculate the voice frequency, presuming the talkgroup ID is somehow "interesting"
4. if "custom tables" are enabled, the scanner looks through the 6 tables, stopping when it finds the first one that satisfies:
ChanLo <= <CC message channel> <= ChanHi
5. the scanner then uses the found table entry to calculate the voice frequency:
Fv = BaseFreq + Step x (<CC message channel> - Offset)

 

[bwigg]

Ok thanks, I was thinking the channel number was from the FCC 800 mhz channel table. Such as when the CC data says go to channel 20 it would use 851.4875 (old FCC 800 table) or 851.2625 (new FCC 800 mhz table). And somehow the custom table by using steps and offsets corrected the channel numbers so it would go to the right freqs.

 

[DonS]

The default channel -> frequency relationship changes based on system type and frequency range. For example, 800MHz "standard", 800MHz "splinter", and 900MHz Mot systems have different default definitions of "channel 20" (851.512500, 851.500000, and 935.262500MHz, respectively). Mot OBT systems (i.e. VHF and "UHF-Lo") don't have reliable, standard channel -> frequency mappings - which is why you always have to enter base/offset/step values for those systems.

The above is why a Mot 3600 system undergoing "rebanding" may need to have all mobile units come in for a new firmware upgrade, and why scanners trying to monitor such a system need to be able to handle specific channel->frequency mappings: Motorola changed their definitions of certain channels (440-559) by 10.987500MHz. E.g. Motorola's channel 440 went from 862.012500MHz to 851.025000MHz.