Digital Communications via Radio

by Thomas Icom

Within recent years the state of the art in digital radio communications has reached the point where consistently reliable high speed systems can be set up at a very reasonable cost. Furthermore, the elimination of morse code as a requirement for an amateur radio license now allows for some interesting possibilities.

The advantage of radio over telephone for digital communications is the simple fact that you don't have to worry about the phone companies or phone bills. Using radio costs nothing except for the initial outlay in equipment. Also, activities such as networks and large-scale digital conferences are accomplished easier when done via radio. Radio communications eliminates the need to commit telecommunications fraud, a common downfall of phone users. Finally, freed from the restriction of phone lines, we can begin to see truly portable operation. You can literally be anywhere and be able to get into the net. Complete digital radio communications systems exist that can be fit into a briefcase.

A radio signal is also better suited for transmission than a phone line. Due to the restricted bandwidth and noise encountered on a phone circut the speed of digital commo is severely restricted. With radio one can have an almost unlimited bandwidth for incredible data communications speeds (some microwave links have data transmission speeds upwards of 1.4 million bits per second), and can increase power to compensate for noise conditions.

While it is often said that radio isn't as secure as telecom, in reality with the proper encryption it is more secure than listening to a phone due to the simple fact that you are no longer using a telecommunications carrier's network. However , seeing the "security measures" on many "underground" BBSes leads me to believe that even an unencrypted radio data network running on 152.24 Mhz would offer an increase in security. One an also randomly change the physical characteristics of the digital signal (mark/space frequencies, modulation type, communications frequency, RF power level) easier on radio to confuse an intercepter.

There are various protocols being used via radio today. All of these protocols are in common use by amateur radio operators, are easy to employ, and are readily and inexpensively available. In fact, a complete low-end communications digital amateur radio setup can be had for under $100.

The oldest communications protocol used is Baudot. This is a five bit code running at either 45 or 75 baud and is mostly used on the shortwave frequencies (under 30 Mhz.) It is a five bit code and as such is unsuitable for any type of computer file transfers. It is also very inexpensive. Traditional ASCII is also used in various forms. Besides being used with different error checking protocols it is also used in the traditional form on shortwave running at 110 and 300 baud. While not as noise resistant and reliable as Baudot on shortwave it does allow for faster communications and for file transfers at nation/worldwide distances with a minimum of equipment. ASCII also doesn't require 5 to 8 bit translation as does baudot for computer use. (In the old days, people used mechanical teletypewriters for data commo and a 5 bit code was simple to work with, given the equipment. Computers were still big clunky things that took up whole rooms.) Someone with moderate knowledge in electronics could make an ASCII radio modem with an XR-2206 and XR-2211 FSK chips for under $20! There is also an error checking form of ASCII used on shortwave called AMTOR (AMateur Teleprinting Over Radio) which is a variation of the STIOR system used by ships.

Finally, we have packet. Packet is a radio based data communications protocol used by ham radio operators for their own computer network that stretches over most of the country. It uses ASCII with a communications protocol called AX.25. AX.25 is a ham radio adaptation of the X.25 protocol used by Telenet and other telecom based data networks. Packet is very active on VHF and UHF frequencies (2 meters, 220 Mhz, 440 Mhz., and above) and is ideally suited to these frequencies. The major east coast ham packet network EASTNET runs from Maine to Miami and contains hundreds of relay stations (digipeaters) and BBSes as well as gateways; stations which provide crossband operation to smaller more local nets running on a different frequency or to shortwave stations which provide connections to the west coast network. There are now also ham satellites in orbit which can extend the range to Europe and other parts of the globe. Access is either directly through the satellite or via a land based gateway in the net. Packet allows for more reliable connections and more portable operation. Instead of running a shortwave transceiver that requires a large power supply and antenna one can fit a laptop computer, TNC (Terminal Node Controller; a modem for packet operation), a VHF/UHF handheld, and a small gel-cell battery in a briefcase. This set-up will go 10-20 miles which is enough of a distance to get to a digipeater from anywhere in the U.S. and access the net.

Radio modems/TNCs are available from ham suppliers along with the respective radios. Check out ham magazines (73, QST, CQ) for supplier addresses and equipment reviews. Also check out the sources listed in my previous articles for more genera l info on radio communications and getting a ham license.

As you see, radio offers as good if not better digital communications capability than the telecommunications network does, with better capability in security. Should you be seriously interested in digital commo it worth your while to check out radio as a means of transmission.

Back to Cybertek Index