William R. Walsh spreads lies when he sneeringly spouts off with: It is a "baseband" adapter, whatever that means. Standard RJ11 phone cable and connectors were used to connect the adapters together, and to a "hub" of sorts. The adapters were not only attached to each other (a bus topology), but each "bus" was connected at a central hub, creating a series of connected "subnetworks" at the point of the hub. As for the purpose of T and W plugs, W is identified as being a "Wrap Plug" in my manual, and "T" as a terminator plug. The T plugs were plugged into the second jack of the last adapter on a "line". If you took the "T" plug out of the adapter, the whole line of computers failed to work (like a string of XMAS lights), but other computers on other "subnetworks" would still work. As for the "W" plug, it was put into any of the unused ports on the hub. If it was taken out, the hub would fail to work at all. Also, the hub did not allow communication between clients on two (or more) different "subnetworks" attached to it. This made it necessary to have at least one computer that had a printer on each "subnetwork". The server (if any was used) went into its own special port on the "hub" that could communicate with any of the other connected "subnetworks". As for the insides of the "T" and "W" plugs, it looks like there is
some kind of resistor in the "T" (clear) plug. The "W" plug has something
in it, but I don't know what it is. Too dark brown to tell for sure.
IBM PC NETWORK-BROADBAND IBM's broadband PC Network addresses the specialized requirements of customers who are combining their LAN with other services, such as video, voice, security and/or additional data channels on a common broadband medium. It may also be used to meet the requirements of small businesses and individual work groups. IBM PC NETWORK ADAPTER II: The IBM PC Network Adapter II is a feature card for connecting the new IBM Personal System/2 Model 30 and IBM Personal Computers to the broadband IBM PC Network. It is compatible with the form factor and bus design of the original Personal Computer, yet it is designed to take advantage of greater Intel 80286 and 8086 processing speeds. The IBM PC Network Adapter II supports the NETBIOS interface and the 802.2/Logical Link Control (LLC) protocols via the IBM LAN Support Program which was also announced today. This allows the adapter to provide access to IBM PC Network and IBM Token-Ring Network applications written to the NETBIOS or APPC/PC interfaces. The IBM PC Network Adapter II is also compatible with the protocols of the original PC Network Adapter via the IBM PC Network Protocol Driver program which was also announced today. This allows the adapter to take advantage of the same protocol and interface as the original IBM PC Network. See IBM Product Announcement 187-079, dated April 2, 1987, for details. IBM PC NETWORK ADAPTER II/A: The IBM PC Network Adapter II /A is a feature
card specifically designed for connecting the new IBM Personal System/2
Model 50, Model 60, Model 80-041, and Model 80-071 computers to the broadband
IBM PC Network. It is compatible with the form factor and bus design of
these new Personal System/2s to take
PC Network Baseband (?) 
I think this is the original 2Mbit/Sec PC Network. The port is a BNC. The module is shown without the EMC cover. I have a similar card that has the module used in the broadband
adapter above. Possibly this card/module combination could be used as a
baseband or broadband with the swapping of the module. The slot cover and
module are attatched to the base card with two screws. To swap the module,
you unscrew both screws on the back of the base card and then screw on
the new module after plugging it in the socket.
AdapterId EFEF "PC Network Adapter " Type, Memory Location, Interrupt Level
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