Digital modulation

New for March 2023. Digital modulation is what moves 99% of wireless data around the planet.  We don't have a reference to back up that claim but pretty much the only popular analog modulations left are AM and FM radio, citizen's band and ham radio. Along rural highways, AM radio allows you to get your free, daily dose of Boomer "classic rock", listen to a fake "program" that wants to sell you the snake oil, or have the latest conspiracies drummed into your head. Light up a Winston 100 and enjoy your trip into the past.  Luddites be warned, that those golden years are coming to an end for more than one reason.

In case you did not know the difference, a radio "broadcast" comes from a single source so that everyone who tunes in gets the same content at the same time (unless you record it for playing back later).  Streaming provides unique data to individual users when they request it. If you suggested to a radio engineer in the 1970s that streaming audio and video would replace broadcasting, they would have laughed and said it would never be possible. But here we are, thanks to Moore's Law and mega-woman-years of digital modulation research and development.

Some vocabulary for digital modulation is provided below:

  • Bits: bits are the least-common denominator of signal information.
  • Symbols: these are units of digital information, at a hierarchy above bits.  For example, one symbol can hold three bits of information.
  • Shift keying: how a signal is altered to transition between digital values (0 and 1 for example)
  • ASK: amplitude shift keying. Amplitude shift keying.  Perhaps the simplest form of digital modulation, where symbols are distinguished by change in signal amplitude.
  • PSK: phase shift keying. Symbols are distinguished by changes in transmission phase.
  • FSK: frequency shift keying. Symbols are distinguished by changes in signal frequency.
  • Binary PSK: Phase shift keying that has only two values (0 and 180 degrees)
  • Quadrature PSK: phase shift keying with four values (0, 90, 180, and 270 degrees)

Here is an excellent video on digital modulation from Professor David Ricketts, of North Carolina State University. He describes the basics of "shift keying" to create a string of data in an RF signal, then covers all of the different digital modulations. We can assure you that if you are new in this field, you will be smarter after you watch Dr. Ricketts' concise explanations. For your further studies, here is his entire playlist on Radio Systems Design.

Professor David S. Ricketts Radio System Design Virtual Course, Module 4, Digital Modulation

Dr. Ricketts has provided a short course on Radio Systems Design at the IMS event for a number of years, where attendees actually build a working radio, including etching the RF circuits.  We'd never want to be behind him at the TSA airport inspection area on the way to such an event, but somehow, he pulls it off!  Here is what appears to be the course outline, but we do not yet know if it will be offered at IMS2023.


Author : Unknown Editor