From: lockhart@mothra.nts.uci.edu (Jack C. Lockhart)
Subject: Re: 800MHz Trunked Radio System Signals
Newsgroups: alt.radio.scanner
Organization: University of California, Irvine
Keywords: The Control channel
Date: 8 Jan 93 00:27:45 GMT

In article <1993Jan6.073502.6495@njitgw.njit.edu> dbm@cats.njit.edu (Dean McDermott - WB2CMN) writes:
>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:
>>>> 

[snip snip - stuff deleted]

>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 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 tranmit
>radios 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 lo 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.

There are two different scenarios we are dealing with here.  You are
referring to Emergency Alert.  

Ericsson General Electric and Motorola Communications defines EMERGENCY
ALERT: a notification feature that lets the dispatcher know the person
who pushed the emergency button is disabled, or unable to talk and/or
needs immediate assistance.  Usually there is no response from the
radio that the emergency button has been activated.

Ericsson General Electric and Motorola Communications define EMERGENCY
CALL: a request to obtain the first available channel using ruthless
pre-emption or top of the queue assignment.

It is possible to have both emergency alert and emergency call
activated at the same time.  Matter of fact, its done all the time.

~jack_

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