Because RFL™ and Hubbell® have a policy of continuous product improvement, we reserve the right to change designs and specifications without notice.
RFL VF-5C RFL Electronics Inc.
October 8, 2012 25 (973)
334-3100
FUNCTIONAL DESCRIPTION
For the following discussion, refer to the functional block diagram of the VF-5C shown in Figure 11,
and typical applications shown in Figures 12, 13 and 14.
Overview
The VF-5C is a 4-wire voice frequency module for an IMUX E1 or T1 multiplexer. It is designed as a
direct replacement for the VF-5A and VF-5AE. Typical applications are transmission only (Figure 12),
push to talk (Figure 13), audio teleprotection tone transmission (Figure 14), etc. The VF-5C accepts
(per channel) a voice frequency 600 ohm referenced input and uses µ-law (in T1) or A-law (in E1)
PCM encoding to convert the analog voice into an 8-bit, 64 kbps digital signal. On the output side of
the VF-5C, the digital DS0 data is decoded into the appropriate analog voice frequency output,
referenced to 600 ohms. The VF-5C can be configured locally via switches or remotely via NMS
software. All settings can be configured and/or monitored remotely except the signaling type selection
which is done with jumpers.
Transmit section
An analog voice input signal is fed into the VF-5C through the module adapter being used. The audio
signal then passes through a balanced input transformer. The transformer output feeds the gain section
which includes a level control IC digitally controlled by the FPGA. The signals are then encoded by
the codec, sent to the FPGA and finally transmitted to the far end through the backplane drivers and
common module.
Receive section
The FPGA receives the appropriate PCM data through the backplane receivers and then passes it along
to the codec. The codec then converts this PCM signal to an audio signal. The output of the codec
feeds the level control stage, where the signal is adjusted to the appropriate signal level and through a
transformer sent to the I/O.
Addressing
The VF-5C has addressing capabilities. The addressing feature uses the least significant bit (LSB) of
the DS0 to transmit the TX address to the far end, where it is compared to the RX address of the far
end. If the address matches, the channel operates normally. However, if the addresses don’t match the
RX channel mutes the output of the channel. This can be used to increase the security of an audio
teleprotection channel.
The address is transmitted as part of a 16-bit message that includes the 7 address bits, 5 checksum bits,
and 4 alignment bits. This structure ensures that no combination of mismatched addresses will be
considered a match. Valid addresses range from 1 to 127. It is recommended that the TX and RX
addresses on a channel be different. The use of the LSB decreases the signal to noise ratio from
approximately 41dB to approximately 35dB.
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