Crystal Radios

28 Feb 2012

The name comes from the natural crystals originally used as a detector to separate the audio from the signal coming in from an antenna.  These crystals are called the detector. (1)  The early detectors were called cat whisker detectors because they used a small wire to probe the crystal to find the best spot where the signal was greatest. (2)

Crystal radios use no power supply and are powered only by the radio waves they are receiving.  Originally these only tuned in AM frequencies, but they can be made for Shortwave and FM radio frequencies as well. (5)

Because they are so low power and quiet they were quickly replaced by vacuum detector and amplifier circuits that drove a loud speaker so that more than one person at a time could listen to the radio.  They are used only only by hobbyist and science classes teaching the fundamentals of radio reception. (1)

At the simplest you need a high impedance ear piece, a diode, an antenna, and a ground.  You wire the ear piece to the diode and to ground on each lead.  You then touch the diode to the antenna and you will be listening to all the strong stations in your area at the same time.  As well as all the noise that the antenna is pulling in.  (2)

The ear piece is not a typical ear plug found in today's modern portable audio devices.  These speakers have a low resistance of just a couple of dozen ohms.  The ear piece you need is a low powered speaker with high resistance of thousands or millions of ohms.  The more sensitive speakers can be told from the less sensitive ear phones by rubbing the end of one wire across a piece of rough metal and listening for a scratching noise in the ear piece. (3)

In order to isolate out one signal you need to build a circuit that oscillates at the frequency you wish to tune in.  This allows all the other frequencies to go directly to ground, while the frequency you are tuning in goes through the diode and into the ear piece.  This also tends to amplify that frequency a little bit. (4)

The tuning of this frequency can be done in several ways.  You can change the number of turns on the coil.  You can change the capacitance of the circuit.  Or you can change the magnetic permeability of the material inside the coil. (1)  

The number of turns on the coil can be adjusted by either sliding a connection over the rails, or connecting a jumper wire to loops brought out for that purpose. (1)  

The higher the selectivity, the more narrowly you are tuning the frequency.  This blocks out more noise, but at the cost of less volume on the ear piece.  The lower the selectivity, the more widely you are tuning the frequency.  This allows more signal to drive the ear piece, resulting in a louder volume, but at the cost of more noise being picked up by the circuit. (7)

You can improve this selectivity by matching the impedance of the antenna to the detector circuit.   You can do this in several ways.  One way is to connect the antenna to the middle of the coil.  Another way is to have another coil that the antenna connects to and then the distance between the main coil and the antenna coil is changed. (7)

    Building Crystal Radios is a good way to become familiar with the basics of electronics.  It is a great intro into the world of physics.  This project is very easy to complete while making a useful end product.  To many people building a radio is like magic.  To be able to build your own and understand how everything works is very rewarding.  The Crystal Radio is a stepping stone to bigger and better electronics projects dealing with amplification and better detector circuits.

References

(1) http://www.oldradioworld.de/gollum/dhistor.htm

(2) Crystal Radio Circuits http://www.techlib.com/electronics/crystal.html

(3) http://en.wikipedia.org/wiki/Crystal_radio.html

(4) http://scitoys.com/scitoys/scitoys/radio/homemade_radio.html

(5) http://solomonsmusic.net/FM_CrystalRadio.html

(6) http://www.techlib.com/electronics/crystal.html

(7) http://www.wikihow.com/Make-a-Crystal-Radio.html

Further references:

Carr, Joseph J. (1990). Old Time Radios! Restoration and Repair. USA: McGraw-Hill Professional. pp. 7–9. ISBN 0830633421.

Petruzellis, Thomas (2007). 22 Radio and Receiver Projects for the Evil Genius. US: McGraw-Hill Professional. pp. 40, 44. ISBN 9780071489294.

Field, Simon Quellen (2003). Gonzo gizmos: Projects and devices to channel your inner geek. USA: Chicago Review Press. p. 85. ISBN 9781556525209.

Schaeffer, Derek K.; Thomas H. Lee (1999). The Design and Implementation of Low Power CMOS Receivers. Springer. pp. 3–4. ISBN 0792385187.

Braun, Ernest; Stuart MacDonald (1982). Revolution in Miniature: The history and impact of semiconductor electronics, 2nd Ed.. UK: Cambridge Univ. Press. pp. 11–12. ISBN 9780521289030.

Riordan, Michael; Lillian Hoddeson (1988). Crystal fire: the invention of the transistor and the birth of the information age. USA: W. W. Norton & Company. pp. 19–21. ISBN 0393318516.

Sarkar, Tapan K. (2006). History of wireless. USA: John Wiley and Sons. p. 333. ISBN 0471718149,.

Bose was first to use a crystal as a radio wave detector, using galena detectors to receive microwaves starting around 1894 and receiving a patent in 1904. Emerson, D. T. (Dec. 1997). "The work of Jagadish Chandra Bose: 100 years of mm wave research". IEEE Transactions on Microwave Theory and Techniques 45 (12): 2267–2273. doi:10.1109/22.643830. Retrieved 2010-01-19.

Sarkar (2006) History of wireless, p.94, 291-308

Douglas, Alan (April 1981). "The crystal detector". IEEE Spectrum (New York: Inst. of Electrical and Electronic Engineers): 64. Retrieved 2010-03-14. on Stay Tuned website

Basalla, George (1988). The Evolution of Technology. UK: Cambridge University Press. p. 44. ISBN 0521296811.

crystal detectors were used in receivers in greater numbers than any other type of detector after about 1907. Marriott, Robert H. (September 17, 1915). "United States Radio Development". Proc. of the Inst. of Radio Engineers (USA: Institute of Radio Engineers) 5 (3): 184. Retrieved 2010-01-19.

Corbin, Alfred (2006). The Third Element: A Brief History of Electronics. AuthorHouse. pp. 44–45. ISBN 1420890840.

Kent, Herb; David Smallwood, Richard M. Daley (2009). The Cool Gent: The Nine Lives of Radio Legend Herb Kent. US: Chicago Review Press. pp. 13–14. ISBN 1556527748.

Jack Bryant (2009) Birmingham Crystal Radio Group, Birmingham, Alabama, USA . Retrieved 2010-01-18.

The Xtal Set Society midnightscience.com . Retrieved 2010-01-18.

Darryl Boyd (2006) Stay Tuned Crystal Radio website . Retrieved 2010-01-18.

Al Klase Crystal Radios, Klase's SkyWaves website . Retrieved 2010-01-18.

Mike Tuggle (2003) Designing a DX crystal set Antique Wireless Association journal . Retrieved 2010-01-18.

Rainer Steinfuehr (2009) Gollum´s Crystal Receiver World Wumpus's Old Radio World website, Berlin, Germany. Retrieved 2010-01-18.

Elmer Memorial Crystal Radio DX Contest, sponsored by Birmingham Crystal Radio Group, Birmingham, Alabama, USA . Retrieved 2010-01-18.

Crystal Radio Building Contest, by The Xtal Set Society midnightscience.com . Retrieved 2010-01-18.

Williams, Lyle R. (2006). The New Radio Receiver Building Handbook. The Alternative Electronics Press. pp. 20–23. ISBN 184728526.

Lescarboura, Austin C. (1922). Radio for Everybody. New York: Scientific American Publishing Co.. pp. 4, 110, 268.

Long distance transoceanic stations of the era used wavelengths of 10,000 to 20,000 meters, correstponding to frequencies of 15 to 30 kHz.Morecroft, John H.; A. Pinto, Walter A. Curry (1921). Principles of Radio Communication. New York: John Wiley & Sons.. p. 187.

Purdie, Ian C. (2001). "Crystal Radio Set". electronics-tutorials.com. Ian Purdie. Retrieved 2009-12-05.

Lescarboura, Austin C. (1922). Radio for Everybody. New York: Scientific American Publishing Co.. pp. 93–94.

Kuhn, Kenneth A. (Jan. 6, 2008). "Introduction". Crystal Radio Engineering. Prof. Kenneth Kuhn website, Univ. of Alabama. Retrieved 2009-12-07.

Fette, Bruce A. (Dec. 27, 2008). "RF Basics: Radio Propagation". RF Engineer Network. Retrieved 2010-01-18.

Payor, Steve (June 1989). "Build a Matchbox Crystal Radio". Popular Electronics: 42. Retrieved 2010-05-28. on Stay Tuned website

Lee, Thomas H. (2004). Planar Microwave Engineering: A practical guide to theory, measurement, and circuits. UK: Cambridge Univ. Press. pp. 297–304. ISBN 9780521835268.

Nave, C. Rod. "Threshold of hearing". HyperPhysics. Dept. of Physics, Georgia State University. Retrieved 2009-12-06.

    Lescarboura, 1922, p. 144

    Binns, Jack (November 1922). "Jack Binn's 10 commandments for the radio fan". Popular Science (New York: Modern Publishing Co.) 101 (5): 42–43. Retrieved 2010-01-18.

Klase, Alan R. (1998). "Crystal Set Design 102". Skywaves. Alan Klase personal website. Retrieved 2010-02-07.

list of circuits from the wireless era can be found in Sleeper, Milton Blake (1922). Radio hook-ups: a reference and record book of circuits used for connecting wireless instruments. USA: The Norman W. Henley publishing co.. pp. 7–18.

May, Walter J. (1954). The Boy's Book of Crystal Sets. London: Bernard's. is a collection of 12 circuits

Purdie, Ian (1999). "A Basic Crystal Set". Ian Purdie's Amateur Radio Pages. personal website. Retrieved 2010-02-27.

Kuhn, Kenneth (Dec. 9, 2007). "Antenna and Ground System". Crystal Radio Engineering. Kenneth Kuhn website, Univ. of Alabama. Retrieved 2009-12-07.

Marx,, Harry J.; Adrian Van Muffling (1922). Radio Reception: A simple and complete explanation of the principles of radio telephony. USA: G.P. Putnam's sons. pp. 130–131.

Williams, Henry Smith (1922). Practical Radio. New York: Funk and Wagnalls. p. 58.

Putnam, Robert (October 1922). "Make the aerial a good one". Tractor and Gas Engine Review (New York: Clarke Publishing Co.) 15 (10): 9. Retrieved 2010-01-18.

    Lescarboura 1922, p.100

Collins, Archie Frederick (1922). The Radio Amateur's Hand Book. USA: Forgotten Books. pp. 18–22. ISBN 1606801198.

    Lescarboura, 1922, p. 102-104

Hausmann, Erich, Ed. (1922). Radio Phone Receiving; a Practical Book for Everybody. New York: D. Van Nostrand. p. 48. ISBN 1110371594.

Hayt, William H.; Jack E. Kemmerly (1971). Engineering Circuit Analysis, 2nd Ed.. New York: McGraw-Hill. pp. 398–399. ISBN 070273820.

Kuhn, Kenneth A. (Jan. 6, 2008). "Resonant Circuit". Crystal Radio Engineering. Prof. Kenneth Kuhn website, Univ. of Alabama. Retrieved 2009-12-07.

Clifford, Martin (July 1986). "The early days of radio". Radio Electronics: 61–64. Retrieved 2010-07-19. on Stay Tuned website

Blanchard, T. A. (October 1962). "Vestpocket Crystal Radio". Radio-electronics: 196. Retrieved 2010-08-19. on Crystal Radios and Plans, Stay Tuned website

The Principles Underlying Radio Communication, 2nd Ed., Radio pamphlet no. 40. USA: Prepared by US National Bureau of Standards, United States Army Signal Corps. 1922. pp. 421–425.

    Hausmann 1922, p. 57

Paul J. Nahin, Paul J. (2001). The science of radio: with MATLAB and Electronics Workbench demonstrations. USA: Springer. pp. 60–62. ISBN 0387951504.

Technical discussions of impedance matching in crystal radios can be found in Ben H. Tongue (2007) Practical considerations, etc., Crystal Radio Set Systems: Design, Measurement, and Improvement; Ben Tongue personal website and Berthold Bosch (2002) Crystal Set analysis, Gollum's Crystal Receiver World

Smith, K. c. a.; R. E. Alley (1992). Electrical circuits: An introduction. UK: Cambridge University Press. p. 218. ISBN 0521377692.

Alley, Charles L.; Kenneth W. Atwood (1973). Electronic Engineering, 3rd Ed.. New York: John Wiley & Sons. p. 269. ISBN 0471024503.

Tongue, Ben H. (2007-11-06). "Practical considerations, helpful definitions of terms and useful explanations of some concepts used in this site". Crystal Radio Set Systems: Design, Measurement, and Improvement. Ben Tongue personal website. Retrieved 2010-02-07.

Bucher, Elmer Eustace (1921). Practical Wireless Telegraphy: A complete text book for students of radio communication, Revised Ed.. New York: Wireless Press, Inc. p. 133.

Marx & Van Muffling (1922) Radio Reception, p.94

Stanley, Rupert (1919). Textbook on Wireless Telegraphy, Vol. 1. London: Longman's Green & Co.. pp. 280–281.

Collins, Archie Frederick (1922). The Radio Amateur's Hand Book. USA: Forgotten Books. pp. 23–25. ISBN 1606801198.

Kuhn, Kenneth (March 1, 2008). "Tapping Inductors". Crystal Radio Engineering. Kenneth Kuhn website, Univ. of Alabama. Retrieved 2009-12-07.

Hadgraft, Peter. "The Crystal Set 5/6". The Crystal Corner. Kev's Vintage Radio and Hi-Fi page. Retrieved 2010-05-28.

Wenzel, Charles (1995). "Simple crystal radio". Crystal radio circuits. techlib.com. Retrieved 2009-12-07.

Hogan, John V. L. (October 1922). "The Selective Double-Circuit Receiver". Radio Broadcast (New York: Doubleday Page & Co.) 1 (6): 480–483. Retrieved 2010-02-10.

Alley & Atwood (1973) Electronic Engineering, p. 318

Marx & Van Muffling (1922) Radio Reception, p.96-101

U.S. Signal Corps (October 1916). Radiotelegraphy. USA: Government Printing Office. p. 70.

Marx & Van Muffling (1922) Radio Reception, p.43, fig.22

Campbell, John W. (October 1944). "Radio Detectors and How They Work". Popular Science (New York: Popular Science Publishing Co.) 145 (4): 206–209. Retrieved 2010-03-06.

Harte, Bernard (2002). When Radio Was the Cat's Whiskers. Rosanberg. pp. 149–150. ISBN 1877058084.

Lee, Thomas H. (2004). The Design of CMOS Radio-Frequency Integrated Circuits. UK: Cambridge University Press. pp. 4–6. ISBN 0521835399.

Stanley (1919) Text-book on Wireless Telegraphy, p.282

    Hausmann (1922), p.60-61

    Lescarboura (1922), p.143-146

    Stanley (1919), p. 311-318

Gernsback, Hugo (September 1944). "Foxhole emergency radios". Radio-Craft (New York: Radcraft Publications) 16 (1): 730. Retrieved 2010-03-14. on Crystal Plans and Circuits, Stay Tuned website

Douglas, Alan (April 1981). "The Crystal Detector". IEEE Spectrum (Inst. of Electrical and Electronic Engineers) 18 (4): 64–65. Retrieved 2010-03-28.

Kuhn, Kenneth A. (Jan. 6, 2008). "Diode Detectors". Crystal Radio Engineering. Prof. Kenneth Kuhn website, Univ. of Alabama. Retrieved 2009-12-07.

Kleijer, Dick. "Diodes". crystal-radio.eu. Retrieved 2010-05-27.

The Principles Underlying Radio Communication (1922), p.439-440

Bucher, Elmer Eustace (1921). Practical Wireless Telegraphy: A complete text book for students of radio communication, Revised Ed.. New York: Wireless Press, Inc. pp. 134–135.

Field 2003, p.93-94 Lescarboura (1922), p.285 Collins (1922), p. 27-28 Williams (1922), p. 79

The Principles Underlying Radio Communication (1922), p. 441

Payor, Steve (June 1989). "Build a Matchbox Crystal Radio". Popular Electronics: 45. Retrieved 2010-05-28.

    Field (2003), p. 94

Bondi, Victor."American Decades:1930-1939"

Peter Robin Morris, A history of the world semiconductor industry, IET, 1990, ISBN 0863412270, page 15

    http://earlyradiohistory.us/1924cry.htm

Polyakov V.T. "Simple receivers for AM signals", ISBN 5-94074-056-1 (in Russian) Radio-Electronics, 1966, №2

QST [Amateur Radio Magazine] January 2007, "High Sensitivity Crystal Set" <http://www.arrl.org/qst/2007/01/culter.pdf>