Part One
Rick Fearns, K6VE
Much has been made and said about digital forms of communications and the use of it in Amateur Radio, but relatively little is understood by most amateurs as to how it really works. References to digital transmissions are often more misunderstood than understood. This is the first in a series of articles that will attempt to unscramble the mystery and misconceptions surrounding digital technologies in ham radio. We’ll also discuss the advantages and disadvantages (yes, there are disadvantages) of digital forms of communications versus traditional analog methods.
First of all, you need to know that all radio waves are analog, not digital. A radio wave is a sine wave, and thus continuously variable between zero and a defined value, either positive or negative. ANY RADIO WAVE THAT IS TRANSMITTED THROUGH THE EITHER IS ANALOG. Wireless signals are always analog. Wired signals may be analog or digital. That’s because a digital signal is one that’s interrupted. CW (Continuous Wave) is inherently an analog signal that’s interrupted, so in a stretch you might call CW a digital signal. The medium (namely the carrier) however, is still analog.
But what about voice? A digital radio voice wireless “signal” is one that was converted from an analog source by sampling that source any number of times, and then assigning a level of amplitude to each sample. The result is a genuine digital signal. When it’s transmitted via radio however, it must be applied to an analog carrier. Yup, that’s right. It must be applied to an ANALOG medium (carrier). Thus, a digital signal must be applied to an analog carrier by using one of the tried and true modulation techniques, Amplitude Modulation, Frequency Modulation or Phase Shift Modulation. In digital terms, we modulate the analog carrier by “keying” it with digital modulation. Technically, we are applying ASK, FSK or PSK to an analog carrier. The type of digital scheme that we apply to an analog carrier is often referred to as a format. There are several popular digital modes or schemes (formats) in use on our amateur bands. A few of the more popular ones are: D-Star, C4FM, DMR, Packet, PSK31, RTTY, AMTOR, PACTOR, G-TOR, PACTOR II, CLOVER, MT63 and JT-65. As you can see from the many forms of digital communications I’ve just listed, we’ve barely scratched the surface of learning to understand the world of digital communications in amateur radio.
Moving to the editorial side of the “Understanding Digital” article that you’re reading, as applied to amateur radio, I cannot help but mention one potential problem that digital communications presents. It’s the one of compatibility. Because there are so many digital formats used in ham radio, the problem of our not being able to communicate with each other because of incompatibility issues, becomes prominent. We’ll discuss this problem in greater detail, along with other disadvantages as well as advantages of digital communications in amateur radio, in future articles.
