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ham033.txt
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1992-10-03
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2KB
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72 lines
This file is ment to be an overall look
at the GE MARKV trunking system.
The first thing to note about the GE
system is that the repeaters are for all
purposes dumb. That is they have no
controllers in them. They funcion basic-
ally as a dedicated UHF repeater would
if the CTCSS tone where replaced with
an audible tone and then notch filtered
out instead of useing a low pass filter.
This tone is called the busy tone in the
GE system it is sent at a 3khz deviation
for 90 msec at the beginning of a call
and there after at 1khz during all mobil
transmissions except during the select
call tones. The repeaters send the busy
tone on all transmisstions except during
the retransmission of the select call
tones sent by the mobile.
The repeaters do two more things. They
send 90 msc of acquisition tone immidiatly
following the first recipt of the 3khs
deviation busy tone in order that the
mobil recognizes that an active repeater
has been hit. It will also time out and
drop the conversation aproxamatly 3 to 5
minutes after all repeaters become busy.
The mobil and control station radios
operate the same way.
The mobil has what smarts the system
needs to operate. It first scans to find
a clear channel. It then sends 90 msec
of busy tone and listens for 90msec to
see if the aquisition tone is being sent
by the repeater. If it does not see the
tone it will scan for another clear
channel and begin again. If the tone is
decoded the mobil will then send what is
called a collection tone for 90msec
times the number of channels in the
system plus one. This will allow enough
time for all radios on the system not
talking to decode this tone and lock
onto this channel. The Mobil then trans-
mitts a two tone paging signal. All
cars decoding this paging tone will stay
on this channel as long as they continue
to decode a busy tone. All other cars
will revert back to scanning looking for
collection tone. In the event a car goes
thru a fade or is incapable of reciving
the busy tone for any legnth of time it
is dropped from the conversation and
cannot get back unless the other cars
allow the system to drop out and
reinitiate the call.
I hope this explains the GEMARKV
system. If you have any questions don't
hesitate to contact me by EMAIL
Eric B. DeWitt
75025,1153
DOWNLOADED FROM P-80 SYSTEMS