GatesAir Intraplex VF-25, Installation And Operation Manual

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GatesAir, Inc. 2-1
Intraplex Products
Section 2 – Functional Description & Setup
This section’s descriptions refer to one channel; each of the four channels on this module operates
identically. Figure 2-1 shows a simplified block diagram of the VF-25 module.
2.1 Transmit Side
Voice input goes through the module adapter at the rear of the shelf. The input signal goes to a
balanced input transformer. The transformer output goes to an amplifier stage and then passes
through an electronic level control, which allows the input level to be adjusted up or down from the
nominal setting in <0.5 dB increments. The normal factory-set input level is 0 dBm, referenced to 600
ohms, and clipping begins at input level of +3.0 dBm. Jumpers on the module allow the nominal input
level to be set to -16 dBm. The control output then passes to the PCM CODEC, which converts it to an
eight-bit digital signal using µ-law coding.
The M-Lead Detector responds to an IDLE or BUSY signal from the external device. For Types I, II,
and III signaling, a level of -48 volts at the M Lead equals BUSY, ground equals IDLE. For Type V
signaling, ground at the M Lead equals BUSY, open equals IDLE. The M-Lead input impedance is
greater than 20K Ohms.
The Field Programmable Gate Array (FPGA) multiplexes the M-Lead signal together with the eight-bit
output of the PCM encoder and places the resulting bitstream into the user-selectable time slot on the
backplane for transmission in the desired direction. Each channel occupies one time slot; you select
the time slot for Channel 1, and each additional active channel occupies the next sequential time slot.
2.2 Receive Side
The FPGA gets the input signal from the appropriate time slot on the backplane and demultiplexes it.
The E-Lead signal goes to the E Lead driver. When active in Type I, III, and V signaling modes, ground
equals BUSY; open equals IDLE. In Type II signaling, the E-Lead and SG-Lead are both used. When
signaling is active, the E-Lead and SG-Lead are tied together through the E-Lead relay.