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GatesAir
4-1
Intraplex Products
Section 4 – Testing & Troubleshooting
4.1 Local versus Remote Loopback
Every VF-40 module is tested before it leaves the factory. In addition, each module provides local and
remote loopbacks for on-site testing and troubleshooting purposes.
●
The local loopback on the VF-40 module loops back all four channels together and is intended for
use during initial installation and testing. This loopback occurs directly after the analog-to-digital
PCM conversion; that is, the analog audio enters the module, is coded to 8-bit PCM data, and is
then immediately decoded and passed back out as analog.
●
The remote loopback on the VF-40 module allows each channel to be looped back independently,
making it useful for testing one channel while the other channels on the module remain in service.
For this loopback, the analog signal is encoded and transmitted over the T1 circuit, is decoded by
the module at the far end, and is then looped back, re-encoded, and sent back to the originating
end.
T1 or other
aggregate circuit
VF
Port 1
Local Loopback
(all four channels)
Location 1
Location 2
VF
Port 2
VF
Port 3
VF
Port 4
PCM
Coder
Decoder
VF
Port 1
VF
Port 2
VF
Port 3
VF
Port 4
PCM
Coder
Decoder
Remote Loopback
(each channel separately)
Figure 4-1. Local versus Remote Loopback
4.2 VF-40 Loopback Setup Procedure
1.
Activate the desired loopback using P code P2, as described in Section 2.8.1 – P Codes. You
may activate a local loopback of all four channels using the LOOPBACK switch (Switch 1,
position 6; it may be labeled AUX on some modules). When doing a local loopback, test each
channel sequentially.
2.
Verify that the input and output level jumpers for the channel being tested are in the Normal
position (Table 2-3).
3.
Connect the output of an audio signal generator (Hewlett-Packard HP4935A or equivalent) to
the input leads for the desired channel. Insert a 1004 Hz test tone at 0 dBm referenced to 600
Ohms.
4.
Measure channel output at the output leads for the channel being tested. The output should be
0 dBm referenced to 600 Ohms, ±0.5 dB.
5.
Measure signal-to-noise ratio with C message weighting, which should be greater than 33 dB
S/N.
