Moto Type I vs. Type II

[ECPD279]

Perhaps I have not looked in the right places, or maybe I'm just too damned lazy to pore over thousands of search results, but at any rate here is my question.

How would one determine whether a system is type I, II, or IIi based solely upon what you hear on the control channel?

I have the San Quentin State Prison, Type I system in my BC-780 as a Type II system and it seems to work fine, so I've just never bothered to change it. The only difference I can see is that it comes up with normal Type II talkgroups as opposed to the XXX-X style from a Type I system. So, if someone were to stumble across this system as an unknown, how could it be determined to be a Type I short of using Trunker or some other software?

I bow to the wisdom of the Motorola Gurus.

 

[SCPD]

How would one determine whether a system is type I, II, or IIi based solely upon what you hear on the control channel?

*chuckle*

Trying to determine whether a system is Type I or II can be a pain. It takes at least a few seconds of observing the control channel. If there is low (or no) call activity, it could take hours. It ranks high in difficulty with determining whether or not a system is VHF/UHF or 800/900. Since older Type I systems are only found on 800 Mhz, determining the two is closely related.

[ ... and there's the whole issue of figuring out fleet maps ... ]

-rick

 

[DaveNF2G]

If you listen to a Type I and a Type II control channel, they sound different. That's not much help when you encounter a single unknown system unless you have a really good ear, though.

If you hear more than one group of users on the same talkgroup ID in Type II mode, or if several users belonging to a single group come up with different talkgroup IDs, chances are you're monitoring a Type I or Type IIi system.

The system type would seem to make no difference at all in the rare case where the Type I/IIi fleetmap results in the same number of units per group and the same number of groups as are normally available in a Type II system. AFAIK, they would look the same to a scanner.

73 de Dave, NF2G

 

[loumaag]

As both Rick and Dave have pointed out, determining the type of system based only on listening to the control channel is difficult. Not nearly as difficult if you are feeding that sound into Trunker though.

The part of your post dealing with monitoring the system as a Type II intrigued me enough to make me look up the system and do a little math for you. You also asked how would one know, just stumbling across this system it was a Type I system. Hopefully the following will enlighten and provide the way to identify a Type I.

I am going to stick with the differences between straight Type I and Type II systems, and skip those pesky Type IIi systems that can cause more headaches. Type I systems use fleetmaps that specify how systems are organized by number of radios. All Type II systems use a fleetmaps that specify how the systems are organized by Talk Groups. To simplify matters I am not going to get into how the programming is done to defeat the layouts of Type I systems, but basically in a Type II system any radio can talk on any TG in the system as the individual radios are not tied to a particular TG. In a Type I system, this is not the same. Each radio belongs to a sub-fleet, which in turn belongs to a fleet. Each sub-fleet can have a finite number of radios assigned to it. In the example of the San Quentin Prison, the Wall Guards sub-fleet (000-02) can have a total of 512 radios assigned to it. Each one of these radios has a unique number assigned to it that identifies it as part of that fleet (000) and sub-fleet (02). These radio ID’s number between 1024 and 1535 (inclusive). If you monitor this system as a Type II system and your scanner is ignoring the status bits (in other words, it rounds to the closest divide by 16 TG #) then all talk groups you see between 1024 through 1520 belong to this sub-fleet. This means that you might see TG 1040 in a conversation with TG 1104. However, if you have set your radio to the proper fleetmap this conversation will be displayed on TG 000-02. If you have a scanner which is capable of determining status bits then you will routinely see odd TG numbers (when set to Type II) such as 1045, 1047, etc. This is the hint that you are monitoring a Type I system.

The downside of monitoring a Type I system using it set up as Type II is that if you are trying to limit what TG’s you hear you need to set up all possible TG’s within a sub-fleet or else you might miss parts of a conversation taking place which jumps across divided by 16 TG #’s. In the example of San Quentin, used here, to monitor the Wall Guards you would have to have the following TG’s loaded:
1024, 1040, 1056, 1072, 1088, 1104, 1120, 1136, 1152, 1168, 1184, 1200, 1216, 1232, 1248, 1264, 1280, 1296, 1312, 1328, 1344, 1360, 1376, 1392, 1408, 1424, 1440, 1456, 1482, 1488, 1504, and 1520.

Now will all of those talk group numbers appear? Probably not, because probably there are not 512 radios assigned to that sub-fleet. But the question becomes, what numbers did they use, so as a safe bet, all TG’s need to be entered. Now of course you can monitor in OPEN or SEARCH mode, and just take what comes, but unless your good at remembering numbers, you still need to alpha-tag those numbers so that when they appear they show what group they belong to. This system, according to the data here on the site only uses three sub-fleets, if that is accurate you will only have to do the above task a total of three times (with the appropriate numbers of course). Me, I will just set the fleetmap and set the three sub-fleets up and forget about it.

 

[WayneH]

Somewhat simple answer:

This applies to Unidens only since the PRO-96 completely ignores the first four bits (right-most) of the TG ID, the first four bits that are the radio id or are part of it depending on the sizecode. You also have to have the status bit mode turned on or off, whatever allows you to see talkgroups change when they are patched, or whatever. Once that's done keep an eye on the IDs. Each person, when they initiate a call will have a different talkgroup id. Now, if they respond to a call already in progress then you won't be able to tell as type I uses message trunking (translation: no revert to the CC to authenticate). When you see the ID change with the voice then it's pretty much dead-on for being type I.

If you have a PRO-96 you need to listen to the voice channels in conventional mode. Type I, especially older systems, use low-speed signaling so this causes a single honking sound a lot when they start their call on a voice channel.

-Wayne