Since the radio equipment to be used with the modem was intended for voice, early amateur packet systems used AFSK modems that followed telephone standards (notably the Bell 202 standard). While this approach worked, it was not optimal, because it used a 25 kHz FM channel to transmit at 1,200 baud. When using a direct FSK modulation like G3RUH's packet radio modem, a 9,600 baud transmission is easily made in the same channel. In addition, the baseband characteristics of the audio channel provided by voice radios are often quite different from those of telephone audio channels. This led to the need in some cases to enable or disable pre-emphasis or de-emphasis circuits in the radios and/or modems. Asynchronous framing Another problem faced by early "packeteers" was the issue of asynchronous versus synchronous data transfer. At the time, most personal computers had asynchronous RS-232 serial ports for data communications between the computer and devices such as modems. The RS-232 standard specifies an asynchronous, start-stop mode of data transmission where data is sent in groups (characters) of 7 or 8 bits. Unfortunately, the simple AFSK modems typically used provide no timing signal to indicate the start of a packet frame. That led to the need for a mechanism to enable the receiver to know when to start assembling each packet frame. The method used is called asynchronous framing. The receiver looks for the "frame boundary octet," then begins decoding the packet data that follows it. Another frame boundary octet marks the end of the packet frame. Sharing the channel A number of data "conversations" are possible on a single radio channel over a finite period. Station configuration A basic packet radio station consists of a computer or dumb terminal, a modem, and a transceiver with an antenna. Traditionally, the computer and modem are combined in one unit, the terminal node controller (TNC), with a dumb terminal (or terminal emulator) used to input and display data. Increasingly, personal computers are taking over the functions of the TNC, with the modem either a standalone unit or implemented entirely in software. Alternatively, multiple manufacturers (including Kenwood and Alinco) now market handheld or mobile radios with built-in TNCs, allowing connection directly to the serial port of a computer or terminal with no other equipment required. The computer is responsible for managing network connections, formatting data as AX.25 packets, and controlling the radio channel. Frequently it provides