Digital Equipment VAX 4000 Model 500A Installation Manual page 36

If you want to place the modem farther away from the system, attach a
BC22F extension cable between the BC19N–12 cable connector and the
modem.
If necessary, you can use 4–40 threaded standoffs and a screwdriver to secure
the BC19N–12 to BC22F connection and the BC22F to adapter connection.
5. Refer to your modem documentation for the location of the modem connector.
To connect a second BC19N–12 cable, repeat the same procedure, except insert
the cable into the connector labeled 0–3.
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Extension Cable
MLO-007189