What is your TNC doing? - TNC to Radio

Chapter 5 - TNC to Radio Wiring and Adjustments - Chapter Table of Contents

TNC to Radio

The TNC must be connected to a radio in order to transmit and receive frames. In this chapter, we will discuss the connection between the TNC and the radio. The biggest problem in describing the TNC-to-radio connection is that there are no standards: no standard connectors, no standard use of pins on the same type of connectors, and no standard names for types of signals. Therefore, in this chapter, we will discuss the purpose of the wiring as much as the connecting information.

Required Wires

There are 4 wires required between the radio and TNC: transmit, receive, PTT (Push-To-Talk), and ground. The connector pins that the wires attach to are called by many names. Some of the names will be mentioned in the descriptions below. If your radio or TNC uses a different name, hopefully understanding the purpose of the pin will help you decide which pin to use.

The documentation for your TNC and radio should show you a connector pin-out diagram. Some older radios may only show a schematic for the microphone. At the end of this chapter are some diagrams of popular radios and a typical diagram of a microphone schematic. If you are in doubt about the correct way to wire your radio cable, ask a trusted knowledgeable friend or call the radio or TNC manufacturer. Making an incorrect connection could damage the radio and TNC.

Modulation

The type of modulation affects where the wires are connected to the radio. There are primarily two types of modulating signals in use today: audio and DFSK. Standard 1200 baud packet is audio modulated with two tones, specifically 1200 Hz and 2200 Hz. This type of modulation works well into a standard voice radio. However, most faster modems use DFSK (Direct Frequency Shift Keying) modulation that does not work through a standard voice radio. To use DFSK, one must either modify a voice radio or buy a data radio. Unfortunately, radio manufacturers have been slow at developing data radios. There are some on the market, but, at the time of this writing, not many to choose from. The following descriptions give information for connecting both audio and DFSK modulation.

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