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