NE8392/NE8392C pdf datasheet (

The NE8392C Coaxial Transceiver Interface (CTI) is a bipolar coaxial line driver/receiver for Ethernet (10base5) and Thin Ethernet (10base2) local area networks. The CTI is connected between the
coaxial cable and the Data Terminal Equipment (DTE) and consists
of a receiver, transmitter, receive-mode collision detector, heartbeat
generator and jabber timer (see Block Diagram). The transmitter
output connects directly to a doubly terminated 50W cable, while the
receiver output, collision detector output and transmitter input are
connected to the DTE through isolation transformers. Isolation
between the CTI and the DTE is an IEEE 802.3 requirement that
can be met on signal lines by using a set of pulse transformers
normally available in a standard 16-pin DIP. Power isolation for the
CTI is achieved using DC-to-DC conversion through a power
transformer (see Figure 1, Connection Diagram).
During transmission the jabber timer is initiated to disable the CTI
transmitter in the event of a longer than legal length data packet.
Receive-mode collision detection circuitry monitors the signals on
the coaxial cable to determine the presence of colliding packets and
signals the DTE in the event of a collision. At the end of every transmission the heartbeat generator creates a pseudo collision for a short time to ensure that the collision circuitry is functioning correctly. The heartbeat function can be disabled for repeater applications.