GE Marc V

The product name looks and sounds similar to GE-Mark V, a turbine controller made by General Electric.

In the U.S. and Australia, these systems used analog FM, operated in the 806–869 MHz band, and were primarily used for commercial, non-public-safety trunking.

For example, if the SMR operator had a system in Bloomington and another covering Chicago, many radio models offered an "area" switch.

(Roaming in this use means working with an unknown GE Marc V system the user happened to run across in their travels).

It was similar in format to two-tone sequential paging codes except that, in a GE Marc V system, the first tone was much longer than the second.

This long first tone gave a bigger time window for all the scanning radios to find and decode a two-tone sequence.

This also reduced a falsing problem that existed in larger systems where mobile radios would open up on other users tones as well as intermodulation products occurring in large metropolitan areas.

Since the radio would not transmit unless the ready light was lit, checking output power, frequency, or deviation on the bench or outside the system coverage area required the technician to attach a test box.

The box bypassed the radio trunking logic so adjustments could be made in a conventional single-channel mode.

Antenna forward and reflected power in a vehicle on a working system was typically checked by bringing up a talk channel and transmitting normally.

As soon as the tones were sent, the receiver audio turned on and the radio made a doorbell-like "ding dong" chime to tell the operator the channel was available to talk.

On hearing a matching tone, every radio in the group would do the doorbell chime, display a green, ready indicator, and the speaker audio would turn on.

Since the doorbell sound was annoying, users tended to try to hold the repeater carrier on until the called party answered so they wouldn't have to listen to continual ding-dongs.

If the mobile receiver gets interference or loses the repeater signal for the moment the second selective calling tone is sent, it remains muted, missing the entire conversation.

A modern trunked system with a control channel is more costly and complicated, but sends continual messages for all in-progress conversations.

System documentation shows at least some radio models, including Classic and Centura, were not capable of being programmed for areas near the Mexican Border.