Because RFL™ and Hubbell® have a policy of continuous product improvement, we reserve the right to change designs and specifications without notice.
RFL VF-5A RFL Electronics Inc.
June 28, 2005 15 (973) 334-3100
FUNCTIONAL DESCRIPTION
The descriptions below refer to one channel; each of the two channels on this module operates
identically. A simplified block diagram of the RFL VF-5A appears in Figure 8.
TRANSMIT SIDE
Voice inputs are fed to the RFL VF-5A through the Module Adapter at the rear of the shelf. The input
signal goes to a balanced input transformer. The normal input level is -16.0 dBm, referenced to 600
ohms. An equipment input jack on the front of the module allows injection of a test tone. The
transformer output goes to an amplifier stage, and then passes through the transmit attenuator.
Switches on the transmit attenuator allow attenuation settings from zero (no attenuation) to 24.0 dB, in
0.1 dB increments. The factory setting for this attenuator is 3.0 dB. At this setting, clipping begins at
an input level of -13.0 dBm.
The attenuator output then passes through a test point (TP1 for Channel 1, TP2 for Channel 2) to the
PCM CODEC, where it is converted to an eight-bit digital signal. Maximum level at the test point is 5
Vp-p; above this level clipping occurs. If the transmit attenuator is set to 3.0 dB, a -16.0 dBm input
gives a +4.0 dBm reading at this test point.
The M lead detector responds to an IDLE or BUSY signal from the external device, and lights the
corresponding LED indicators. A level of -48 volts at the M lead equals BUSY; open or ground equals
IDLE. The M lead input impedance is greater than 20K ohms. Finally, the Logic Array multiplexes the
output of the PCM together with the M lead detector signal, and places the resulting bitstream onto a
user-selectable time slot on the backplane for transmission in the desired direction.
RECEIVE SIDE
The Logic Array 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, which activates the LED status indicators.
When active in Type I format, ground equals BUSY; open equals IDLE. In Type II or III, the E lead
and EB lead are both used. When signaling is active, the E lead and EB lead are tied together through
the E lead relay.
The PCM CODEC converts this eight-bit digital signal back to an analog audio signal and passes it to
the receive attenuator, which, like the transmit attenuator, has switches to allow settings from zero (no
attenuation) to 24.0 dB in 0.1 dB increments. The factory setting is 3.0 dB of attenuation for a +7.0
dBm output.
The attenuator output passes to an amplifier stage, and finally through the output transformer to the
output connectors on the module adapter. With a properly calibrated RFL VF-5A set for -16.0 dBm at
the transmitter input, the output level will be +7.0 dBm referenced to 600 ohms. An equipment jack on
the front of the module allows retrieval of the test tone.
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