Comtech EF Data SDM-9220 - Manual (Page 133)

Universal E&M/PTT Interface Card
Memotec Inc. 9-5
9.3 About Push To Talk (PTT)
PTT is a permanent point-to-point connection that is used to key a radio in two different
scenarios:
• Scenario 1: From a remote mobile location to a control station, such as an air
traffic control application. See
Figure 9-2 on “Push-To-Talk Application: Sce-
nario 1” on page 9-6 .
• Scenario 2: Between two remote locations. See Figure 9-3 on “Push-To-Talk
Application: Scenario 2” on page 9-7 .
In both of these scenarios:
• The audio path is always up
• The PTT CONTROL device produces M lead transitions on the E&M connection
• The NetPerformer detects these M lead transitions, and regenerates them as E
lead transitions
• The E lead transitions are transmitted and replayed at the other end of the connec-
tion without clearing the audio path
• As a result, more rapid communications can take place between the two loca-
tions.
9.3.1 Fixed Control Station Scenario
In an application involving communications with a fixed control station (Scenario 1):
• The M lead is permanently connected to Signal Ground at the PTT ANSWER
side, so that the E&M channel is up at all times
• Only the control station operates as a PTT CONTROL device.