Category Archives: Default

The colonial British writer Rudyard Kipling (same guy who wrote The Jungle Book) wrote a book in 1902 called Just So Stories that is now considered a classic of children’s literature. It is a very good book by all accounts and consists of “origin stories” which are fanciful stories about how various animals came toContinue reading “A just-so story: how the QAM got his stars”

Modern electronic communication systems are usually designed to use passband signaling, i.e. the transmitted waveforms have their frequency spectra concentrated in a narrow range of frequencies around a carrier frequency. There are at least two excellent reasons for designing comms systems this way: (1) for fundamental physical reasons explored in another note, wireless links cannotContinue reading “The One True Modulation”

The literature from the early 20’th century on the parallel development of the “wire and radio art” makes for fascinating reading today. In this note, we will look at some excerpts from this article: A. A. Oswald, “Early History of Single-Sideband Transmission,” in Proceedings of the IRE, vol. 44, no. 12, pp. 1676-1679, Dec. 1956, doi:Continue reading “Close Reading – “early wire and radio art””

In theory, we can build wireless comms over a wide range of frequencies ranging from near-DC (i.e. low frequency, very long waves e.g. 1000 mi) to ultra-violet (very high freq, very short e.g. 10-7 m). In practice, there is a small band of spectrum which is, basically, prime EM real-estate. It is easy to understandContinue reading “EM theory for comms – Part 2: Wireless Beachfront Real-Estate”

The modern theory of electronic communication, due to Claude Shannon, is famously abstract. It does not concern itself with the contents of the messages being exchanged, nor with the physics of how the information transfer takes place. From the source: The fundamental problem of communication is that of reproducing at one point either exactly orContinue reading “Basic EM theory for comms engineers – Part 1: Metal Wires”

Here’s an practice problem with diodes that has some interesting aspects to it. This circuit is about as complicated as diode circuits get and performs a simple and potentially useful function. In other words, output voltage varies with the inout in a simple and potentially useful way. Let’s see if we can figure out whatContinue reading “A practice problem with diodes”

In your previous Circuits class, you were introduced to ideal op-amp circuits. In our class this semester, we will be building on this and become familiar with a small number of simple, but very useful op-amp circuits (e.g. inverting and non-inverting feedback amplifiers, integrators, adders and a few variants of these). Meanwhile we have beenContinue reading “Thinking about ideal op-amps”

Starting with this week’s lab, we are going to get comfortable with using an oscilloscope very quickly. Fortunately, modern digital ‘scopes have an accessible interface for simple waveform measurements and are therefore quite easy to get started on. Here’s a very short introductory video on getting started with an oscilloscope: (I really like the KeysightContinue reading “Oscillography”