DSD - DMR finding adjacent sites

thewraith2008

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Nov 22, 2016
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A bit of a long post so hopefully you stick around.

I've been playing some more with the trunking capability of my custom DSD on a TIII DMR (MOT - CAP MAX) network.
I'm currently using a base frequency to work out the absolute frequency of a LCN when I need to switch frequency to follow a call.
On the network/site I'm working with, I've noticed an odd thing with using this approach, read on.

This is a TIII 'Huge' statewide network (many sites) and also has LCNs that are spread out over approx. 25MHz (485-510).
On the site I'm working with, it broadcasts the adjacent sites. One of these adjacent sites does not appear on the frequency where it's expected using the base frequency.
This base frequency I'm using works fine for finding the all other adjacent sites (and the traffic LCNs when on them).
I have verified this odd sites real frequency and Network ID/SiteID and determined the base frequency it should be using to follow traffic on it.

The question is:
How would a real radio switch to this site if needed?
When a real radio is programmed for use on one of these trunked networks, does it:
Just use a base frequency with a list of CC sites and it does the calculation to find an adjacent site (which wouldn't work it seems in the above case).
Or does the radio have a list of all CC sites in the network with the absolute frequency and a base frequency to use so it can look it up when needed.
Or does the radio have a list of all CC sites and traffic channels in the network with the absolute frequency it can look it up when needed.
Or none of the above. What way does the radio do it?

Still here, thanks for listening.
 

DSheirer

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Fulton, NY
I recorded a Capacity Max system at the grand canyon last month that is repeatedly transmitting/alternating between the standard aloha message and a vendor-specific (Motorola) Aloha message. It's broadcasting 1 neighbor site. It's not broadcasting the multi-block explicit channel frequency extension block like I saw on another Hytera Tier-III system, so I'm assuming it's using a fixed base and step size formula.

System: Niles Radio Trunking System, Flagstaff, AZ, Arizona - Scanner Frequencies

The channels are:
916 - Site 22 CC 462.4375
967 - Site 25 CC 462.0750
981 - Site 25 TC 462.2500

This seems to follow a base of 450.0 MHz with a 12.5 kHz channel step size.

This is the proprietary Motorola Aloha:

Code:
99100900F6D065000000C20B
Breaking down the CSBK, there are 3 bytes in the middle that could potentially be used to identify band parameters:

Code:
00 99 10011001
08 10 00010000 motorola
16 09 00001001 <<<
24 00 00000000 <<<
32 F6 11110110 <<<
40 D0 11010000 sic 1101000001100101 Net:1 Site:25
48 65 01100101 sic
56 00 00000000 Target Radio
65 00 00000000 Target Radio
72 00 00000000 Target Radio
80 C20B CRC
I tried mapping these 3 byte values to the C.* tables at the end of TS 102 361-4 but it didn't seem to line up with any of the table entries.

It seems odd that they'd go to the trouble of crafting a vendor specific Aloha message if it doesn't contain something useful like band details.

Denny
 

thewraith2008

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Nov 22, 2016
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For me the CSBK:25 (Aloha) FID:16 is only seen when there has been voice activity. And even then it is infrequent.
After 6pm, the network is dead until about 5am. Excluding almost constant data grants. During this time, CSBK:25 (Aloha) FID:16 is not seen.
Your breakdown of the "Aloha" seems to show that it's completely unrelated to the standard Aloha defined in the standards.
The CSBK:25 (Aloha) FID:16 seems to mostly be repeating whats in the ShortLC but I guess it serves some purpose from a radio perspective.

This still does not explain to me how one site can use a different base frequency as well as how a radio would find any adjacent site with it.
When on this odd site(LCN:642), the listed adjacent site LCNs are all wrong when using the base frequency that works for that site.
 
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