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GatesAir
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-40 module.
2.1 Transmit Side
Voice input is through the module adapter at the rear of the shelf. The input signal goes to a balanced
input buffer. The input buffer 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 <0.1
dB increments. The normal factory-set input level is 0 dBm, referenced to 600 ohms and clipping
begins at an input level of +3.0 dBm. Switches 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 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.
