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AE5ME > ARES 27.03.16 05:48l 11 Lines 3732 Bytes #999 (0) @ WW
BID : TZXPYA23SQLC
Read: GUEST
Subj: Digital Emergency Communcations Series by AD5XJ (SATE
Path: IW8PGT<IZ3LSV<I0OJJ<GB7CIP<N0KFQ<AE5ME
Sent: 160327/0317Z 34292@AE5ME.#NEOK.OK.USA.NOAM BPQ1.4.64
TERMINAL NODE CONTROLLER
External hardware may be used to encapsulate multiple functions. This hardware is known as a TERMINAL NODE CONTROLLER or TNC, often it is just referred to as a modem, and combines a multitude of functions into a ?black box? for the user.
You may not know that modem is an contraction of the terms modulator and demodulator. The TNC is the computer digital side of the hardware ?black box?, the modem is the analog audio side to and from your radio. External hardware often combines both modem and TNC functions in one box.
The TNC will decode the demodulated incoming audio data stream and provide a digital signal that the computer will understand and can display. Or, on transmit it will encode the data for transmission. It is also responsible for the Transmit / Receive switching (PTT). If you have ever used VHF packet, you know it takes a TNC to hook up to the radio and to the computer. It is also possible to send and receive packet on HF, albeit at a much slower rate. The process is the same. Audio signals to and from the radio are converted to digital pulses in the modem, given to the TNC to provide the digitally decoded output to the computer for your packet display program. Often amateurs use the terms modem and TNC interchangeably when referring to external hardware.
The SCS TNC is of the same type modem/controller units as used for PACKET, only using the proprietary PACTOR II, III or PACTOR IV (in the case of the new Dragon hardware) protocol instead of PACKET and at a considerably higher cost. The most recent of additions to the SCS product line is a new Enhanced PACKET TNC with APRS capability for both HF and VHF/UHF. Enhanced PACKET provides a much more robust version of the historic PACKET protocol. It is widely used in Europe on both HF and VHF/UHF.
These days, powerful new computers often perform the same functions as external hardware. The software based, virtual solution, involves using a computer with a sound card. The computer becomes the modem/TNC. The computer sound card output (usually for speakers) is connected to the microphone input or aux transmit audio of the radio, and the audio output of the radio (often the headphone or ext spkr) is connected to the line input of the computer sound card by way of isolating hardware called a computer interface. The interface helps to match the dissimilar hardware aspects of connecting radio and computer. Some radios need a different voltage transition for rig control than is provided by the controlling port on the computer (a USB port or RS-232 Serial port). The computer interface may provide this voltage difference internally and provide the correct rig control output to the radio. In the case of at least one brand there may be a separate cable or hardware box to accomplish the voltage transition for CAT or CI-V control signals to the radio. This connection method is used for at least 20 of the 38 or so digital modes for ham radio. The digital computer interface to radio arrangement provides the hardware connections for PSK, MFSK, AFSK and other audio based digital modes.
Modes such as RTTY and digital FAX can use FSK and must have a separate digital connection from a serial port on the computer, to the direct data FSK input to the radio (if it has one). The radio provides the carrier frequency shift given digital data signals at the FSK port. The higher speed 9600 baud PACKET mode on VHF/UHF, for example, requires this arrangement. The detection of FSK signals is taken directly from the frequency discriminating detector. These received digital signals are then interpreted for display by software on the computer providing the same functionality as the modem external hardware.
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