From: dbm@cats.njit.edu (Dean McDermott - WB2CMN)
Newsgroups: alt.radio.scanner
Subject: Re: 800MHz Trunked Radio System Signals
Keywords: The Control channel
Date: 6 Jan 93 07:35:02 GMT
Organization: New Jersey Institute of Technology, Newark, N.J.

In article <1993Jan5.124700.29874@ms.uky.edu> hgpeach@ms.uky.edu (Harold Peach) writes:
>lrk@k5qwb.lonestar.org (Mr. Lyn R. Kennedy) writes:
>
>>puma@halcyon.com (puma) writes:
>
>>> lrk@k5qwb.lonestar.org (Mr. Lyn R. Kennedy) writes:
>>> 
>>> > This is another typical mis-representation. Unless the transmitting 
>>> > unit is full-duplex, it will continue transmitting, blocking that 
>>> > channel. Even though the system might prevent the next transmission, 
>>> 
>>> If the remote unit that was using the repeater and the remote unit
>>> requesting emergency access are on different incoming frequencies,
>>> why CAN'T the system immediately turn over the repeater channel
>>> to the emergency unit?  What difference would it make if the first
>>> remote unit continued transmitting?
>
>>Say it's a five-channel system and all four talk channels are in use. 
>>There are four mobiles transmitting on the four talk channels. If one 
>>is full-duplex then it could be disabled but that is not common. Even 
>>though the unit needing the emergency access could tell the controller 
>>on the control channel (mobile side), it can't tell one of those other 
>>mobiles to stop transmitting so there is no repeater available. 
>>Whichever one quits first may lose it's repeater but how do you know 
>>it's not something important? Do you wait for the lowest priority one 
>>to stop transmitting? That may be the guy talking the longest.
>>I'm not saying it's a bad plan, it just isn't usually explained 
>>properly.
>
>From a practicle standpoint you are correct, but in the trunked system
>I know of, any mobile unit can be disabled from the control channel.
>Therefore, you could theoretically turn off the transmitter on any
>radio via the data channel.  One of the big advantages to trunking is
>that the transmitter and receiver can be programmed out of a system if
>they are stolen, etc.
>-- 
>Harold G. Peach, Jr.       ><>       N4FLZ       _%       hgpeach@s.ms.uky.edu



EMERGENCY on a Motorola trunked radio is normaly used only when a police officer is in a position of needing help and can not use the radio. The officer hits the EMERGENCY button and the radio keys up on the input to the control channel and send the emergency signal along with the radio ID. EMERGENCY was never designed to give an officer a higher priority to pass a priority message. Once the emergency is received at the dispatchers point the main objective is done. Now if the officer is in a position to us



e his radio he can key up and give additional info when the controler assigns him a repeater. I hope we all agree that only one signal can transmit on one freq at a time. 99.9 percent of the Smartnet (Motorola format for public safety, supports emergency function) radios sold are Not duplex. So if all channels of a trunked system are in use that means that the units assigned to each repeater are in the transmit mode. There is NO way for the repeater controler to send a message to any of these tranmitting r



adios to stop transmitting and give up the channel for the EMERGENCY unit. If the controler assigns the EMERGENCY radio to one of the channels in use you will only end up with two radios stepping on each other. However this is not as important as it seems, since if the officer used the emergency button to start with he most likely is in a situation were he could not call for help himself. At least now that the data channel has received his emergency and alerted the dispatcher officers can start to look if 



the computer shows the officer on a job and a possible location. Compair this to a conventional system were if a unit is transmitting NO other signal can get thru with even an emergency call.
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