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: 5 Jan 93 19:46:33 GMT
Followup-To: alt.radio.scanner

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]


I guess I started this mess.  Sorry about that. 

lrk@k5qwb.lonestar.org (Lyn R. Kennedy) is absolutely correct.  A
radio can only be prohibited from transmitting when it is in the
receive mode or if it is operating full duplex.  

I just got off the telephone with the system engineers of Motorola in
Illinois and Ericsson GE in Virginia.  Both tell me the following:

In both systems you have a choice of ruthless pre-emption or placing
the emergency call at the top of the queue.  Both manufacturers
recommend using the top of the queue method because the mobile,
portable or control station who is transmitting (and will be blocked
from further communication on the pre-empted repeater) may be closer
to the trunk radio site than the station who has originated the
emergency call.  This means that the pre-empted station captures the
repeater until one of two things happens: they release their PTT
button or they time out.  BTW, the pre-empted transmitting station is
sent a disconnect code and returns to the data channel after release
of the PTT or timeout.

When a station makes a emergency call, all mobiles, portables and
control stations in the talk group being pre-empted are sent a discon-
nect code and immediately return to the data channel.  Most Ericsson
and Motorola radios are not full duplex.  They are simply too small
for hardware necessary to accommodate full duplex operation.

So, if the controller is programmed to perform ruthless pre-emption,
the control channel would reassign the pre-empted repeater to the unit
making the emergency call.  However, the possiblity and probability
exists that a part or all of the emergency call stations transmission
will be blocked.  This will occur if the pre-empted transmitting
station has captured the repeater.

The reason why I researched this so comprehensively is because all 13
of the University of California campuses and hospitals will have a
request for quote on the street this year and I am expected to help
evaluate the bid.  I guess I learned something today.

I hope this clears up the confusion.  

73

~jack_

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Newsgroups: alt.radio.scanner