EDACS Extended Addressing (EA) Decoding

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EricCottrell

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Hello,

I recently picked up on decoding EDACS Extended Addressing (EA) again, since now I can actually hear the voice traffic on the local system. In going over some notes and logs I discovered a few more details I missed.

Since EA changed the meaning of some of the messages, I wondered how to detect an EA system and what technique is used to prevent a non-EA radio from trying to use a EA system. The radio compares the site id with the value programmed in the radio. If there is a match, it uses the site.

On non-EA systems the site id is contained in a message that has the data bits
Code:
dd ccccc ppp h ff iiiiii
where d is the slot delay, c is the control channel, p is the priority level, h is home flag, f is failsoft, and i is the site id. The site id is 6 bits so there are 64 possible site ids.

On EA systems the same message is used but the control channel is sent in another message. The site ids are in the range of 33 to 63 but the specifications say hundreds of sites are possible. So there are id bits somewhere else.

I had a doh moment today when I looked at the site id messages from several EA systems. I suspect that non-EA systems had a site limit below 32 sites even with six bits assigned. Setting the msb of the site id would prevent a non-EA radio from getting a match during the site id comparison. If I eliminate that bit, and use the former control channel bits, I get a match for reported site ids. So a EA system has a site id message of
Code:
dd iiiii ppp h ff eiiiii
where e is set one to indicate extended addressing. I assume the d, p, h, and f bits have the same meaning on either system. This means that an EA system can have up to 1,023 sites.

The side effect with the original trunker-based programs is when system ids of 32 to 63 (20 to 3f in hex) come up then it is an EA system and can not be tracked.

73 Eric
 

SCPD

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Eric said:
I recently picked up on decoding EDACS Extended Addressing (EA) again, since now I can actually hear the voice traffic on the local system. In going over some notes and logs I discovered a few more details I missed.
Welcome back!

Eric said:
So a EA system has a site id message of
Code:
dd iiiii ppp h ff eiiiii
where e is set one to indicate extended addressing. I assume the d, p, h, and f bits have the same meaning on either system. This means an EA system can have up to 1,023 sites.
Eric - please look at your Unitrunker logs; you will see the message "Site Pro Site" displayed for this code word along with the decoded site number. The logic for this (which I haven't touched in a few years) assumes an 8 bit site ID. The extra site bits come from the region you described. This works very well in Florida.

Folks wanting to enable decode logging can do so by checking the Decode "Log" option in their Receiver settings. Click on the Folder icon to see the directory where the decode logs are stored. Log files are "rolled" at local midnight. The previous day's log is GZIP compressed to save space. The log file's name is the year/month/day it was created.
 

SCPD

QRT
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Feb 24, 2001
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Location
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On a related note, I just realized I was within striking distance of Cecil County, MD about six months ago.

*groan*

Does anyone have current Unitrunker logs for this system?
 
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