Digital radios can be considered to be (D)ata (C)ommunications (E)quipment or DCE much the same as an external telco modem. Usually, but not always, the radio transmit function is accomplished by the (R)equest (T)o (S)end or RTS control line. An exception is if the radio is designed to key on data when data are present. Some means of controlling the transmit and receive of the radio is necessary for half-duplex or (T)ime (D)ivision (D)uplex, TDD---the operating mode of many transceivers.

The familiar DB25 or DB9 fitting is usually the data port connection and is---often but not always---wired to the EIA/TIA standard for the connector used. (Note: to prevent expensive damage, it pays to double check a port pinning before connecting to an accessory since some manufacturers do non-standard  wiring.)

A few of the common interface standards for radio modems are: EIA/TIA/RS232, 574, 485, 530, and V.35. Generally, the EIA232 and the EIA530 are DB25 connectors; the 574, a DB9; and the V.35 can be either a 25 pin or a large "Winchester" fitting. "Gender-menders" and other kinds of adapters are available for connecting to testing equipment if an "odd" coupling is encountered.

When a connection is made to a PC or other type of (D)ata (T)erminal (E)quipment, DTE---the data cable length becomes an important factor in obtaining reliable communication. Short runs of 15 or 20 feet can be used with EIA/RS232 or 574 data. Longer runs require a balanced data line to reduce interference to and from the cable and to keep the "copper" losses at a minimum. The EIA/RS485 and the 530 standards are useful here. For higher data rates and where a multiplexer or synchronous communication is desired, the V.35 is a common choice.

Async (asynchronous) data is the most prevalent data format in the PC world. Start and stop bits are included with the data bits to "frame" the data word, keeping it synchronized during a data stream. Sync (synchronous) data does not use the start and stop bits so "clocking" is needed to keep the data word in step. Usually the transmit and receive clock signals are carried on the data cable separately from the data and control lines.

To successfully bring a new radio data system on line or diagnose a "problem" circuit, some testing devices are necessary. The radio link is checked first to make certain the signals get from "here to there". The antenna , with its many associated parts, is very important for reliable communication. The basic test instrument for checking the antenna and transmitter power is an SWR/Power meter.

Once the radio link is established, then data are sent and checked for errors. It is necessary to send "known" data other than the data used with the network. A "Quick Red Fox...." generator, QRF-1  or a simple PC polling program are very handy tools for quick checks. A (B)it (E)rror (R)ate (T)ester, BERT is used to verify the quality of received data , but this test is necessilary lengthy to establish the correct error level.

Before the data cable is connected to the radio, the pinning can be checked using a data port tester. The plugin device is simply a group of LED's that indicate the activity of a pin that is associated with each light. Immediately, the TRQ-1 can tell if a connector is wired correctly and if the data and control lines are as planned. The 25 pin sync model includes the clocking pins.

If RTS control for transmitter keying is needed, then a KODrs (K)ey (O)n (D)ata device takes care of turning on the radio's transmitter when data are present. If converting from EIA/RS530/V.35 to EIA/RS232 is required, a converter is available. Also for EIA/RS485 to 232.

Click "Products" for more information on the devices described here.