Superheterodyne Radios Explained

The general public thinks there is one thing called a radio. Sure, they know there are radios that pick up different channels, but other than that, one radio is pretty much like the other. But if you are involved in electronics, you probably know there are lots of ways a radio can work internally. A crystal set is very different from an FM stereo, and that’s different still from a communications receiver. We’d say there are several common architectures for receivers and one of the most common is the superheterodyne. But what does that mean exactly? [Technology Connection] has a casual explanation video that discusses how a superhet works and why it is important. You can see the video, below.

Engineering has always been about building on abstractions. This is especially true now when you can get an IC or module that does most of what you want it to do. But even without those, you would hardly start an electronics project by mining copper wire, refining it, and drawing your own wire. You probably don’t make many of your own resistors and capacitors, neither do you start your design at the fundamental electronic equations. But there’s one abstraction we often forget about: architecture. If you are designing a receiver, you probably don’t try to solve the problem of radio reception; instead you pick an architecture that is proven and design to that.

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Simple Superheterodyne SW Receiver Harks Back Almost 100 years

Early radio receivers worked on a principle called Tuned Radio frequency (TRF), patented in 1916. They weren’t very easy to use, requiring each stage to be tuned to the same frequency (until ganged capacitors made that a bit easy). The Superheterodyne design, devised in 1918, was superior, but more expensive at that time. Cost considerations led adoption of the Superhet design to lag behind TRF until almost 1930. Since then, until quite recently, the Superhet design has been at the heart of a majority of commercial radio receivers. Direct Conversion Receivers were devised around 1930, but required elaborate phase locked loops which restricted their use in commercial receivers. The point of all this background is that the Superhet design has served very well for more than 90 years, but will soon be rendered redundant once Software defined Radio (SDR) becomes ubiquitous. Which is why this study of the simple Superheterodyne shortwave receiver deserves closer study.

[Dilshan] built this two transistor and two IF transformer based superheterodyne radio designed to receive 13m to 41m bands. The whole build is assembled on a breadboard, making it easy to teach others to experiment. [Dilshan] offers very useful insights into antenna, rod coil and IF transformer parameters. To dive in to Radio architecture, check this post on Amateur Radio. And if you would like to get a closer look at Antique Radios, check this post on Restoring Antique Radios.