14 May 2004

The Voice of the Crystal

Sheldon Greaves, Managing Editor and Webmaster

CH. Peter Friedrichs. The Voice of the Crystal. How to Build Working Radio Receiver Components Entirely from Scratch. 1999. ISBN
0-9671905-0-9. Click to order this item from the SAS store.

When I was about eleven, I found an old book from the 30's or 40's at a local library book sale that contained science projects for young boys. One of these was a crystal radio. Excited as only a kid can be, I set out to build it. I gathered the required parts, including a brand-new spool of 28-gauge wire, and cobbled the thing together. It didn't work. I tried to figure out why, but knowing next to nothing about what I was trying to do, I grew discouraged and gave up. Now, many years later, I have some insights into why my crystal radio failed to function, and I owe most of those insights to reading Pete Friedrichs' book.

The crystal radio is part of the American technological mythos. It has become a metaphor for homebrew, do-it-yourself ingenuity and with good reason. While it may seem crude when compared with today's sophisticated consumer electronics, in the earlier decades of the previous century crystal radios represented a remarkably advanced technology lovingly hand-crafted in thousands of basements, attics, and garages. Moreover, these projects often constituted the early steps taken by countless budding scientists and engineers who went on to design today's high-tech wonders.

Crystal radio technology seems to be undergoing a renaissance among hobbyists and tinkerers. Much of the impetus can be ascribed to a flurry of new publications on the subject, and one of the most remarkable is "The Voice of the Crystal." The subtitle, "How to Build Working Radio Receiver Components Entirely from Scratch," is no hyperbole. When author Peter Friedrichs says "from scratch", he means it. I read with growing fascination about how he turns wire, wood, bits of tubing, metal cans, nuts and bolts and various other items scavenged from God-knows-where into working radio components. Not once is one required to visit the local Radio Shack or other electronics supply store in order to buy anything more elaborate than wire or an alligator clip.

Now, I confess when I first saw the book and read the subtitle, I surmised that this book might be too much of a "niche item," something only for subspecialists of a dying art. But this book is broadly educational in a way I never expected.

Earlier I referred to mythology. There is a perception among the non-technical public, no doubt encouraged by popular media and science fiction, that there exists a breed of technical wizards who can transform commonly available materials into a working phaser cannon or turn a deck chair into a hovercraft. The underlying basis of this belief, it seems to me, is the perception that these super-tinkerers know deep, super-obscure facts of physics and chemistry. What Friedrich demonstrates through this book, however, is that understanding the basics of science, not the obscurities, is what make his technical marvels a reality. The basics taught here apply across many areas of physics and electronics, and the problem-solving approach implicit in this book will serve the reader well, no matter what their ultimate field.

This brings me to the text of the book itself. Friedrichs' prose is exemplary in its clarity and precision, literary attributes for which engineers as a group are not noted. He understands how to take you through a concept, such as resonance or impedance, so that you understand it. Moreover, you understand how it informs what you are trying to build. This is the great advantage of taking the "from scratch" approach. At the end of the day you know why things work, and not just that tab A goes into slot B.

Now, on to specifics. After a brief but useful discussion of basic theory, Friedrich goes on to discuss different kinds of headphone components. One uses a shoe polish can and a doctor's stethoscope among other items. Though not the most elaborate, my personal favorite is the headphone driven by the piezo crystal scavanged from a cigarette lighter (see Figure 1, above). The sheer simplicity and elegance of this project alone is worth the price of the book.

From there, he goes on to detectors, explaining the theory behind them and the design considerations germane to building them. Most of the detectors employ a crystal or something similar. Next come condensers, including a fiendishly clever design for a variable condenser using overlapping leaves of roofing metal (Figure 3). Coils are treated next, which turns out to be a more elaborate discussion than I was expecting. The crank coil project (Figure 4) is worth a good, long look. Still, like the rest of the book it remains clear and infects you with the author's enthusiasm for his subject. Sections on simple tuners, antennas, and assorted circuits and formulae round out this book.

One other thing you will note is the artistry that goes into the components described here. I've included some color photos of some of these; the black-and-white photos in the book don't really do them justice. Some of these components are remarkably pleasing aesthetically and would not look out of place in an art gallery. If nothing else, they display a degree of care and craftsmanship that reflects the best traditions of the home experimenter.

Whether or not you plan to build your own crystal set, this book is a delightful read. Frankly, I couldn't put it down. I can't think of a better way for a fledgling scientist--young or not so young--to make a beginning at learning the secrets of nature.