<h1>Crystal Radio Set Systems: Design, Measurement and Improvement</h1>


The main purpose of these Articles is to show how Engineering Principles may be applied to the design of crystal radios.  Measurement techniques and actual measurements are described.  They relate to selectivity, sensitivity, inductor (coil) and capacitor Q (quality factor), impedance matching, the diode SPICE parameters saturation current and ideality factor, audio transformer characteristics, earphone and antenna to ground system parameters. The design of some crystal radios that embody these principles are shown, along with performance measurements.  Some original technical concepts such as the linear-to-square-law crossover point of a diode detector, contra-wound inductors and the 'benny' are presented.

Please note:  If any terms or concepts used here are unclear or obscure, please check out Article # 00 for possible explanations.  If there still is a problem, e-mail me and I'll try to assist (Use the link below to the Front Page for my Email address).
Second note: The two dates following the Article titles are, respectively, the original publication date and the date of the last revision.

Content of Articles in Section A of this Site
Article #
Practical design considerations, helpful Definitions of Terms and useful Explanations of Concepts used in this Site: 04/25/00;  11/06/07 
A New Way to Look at Crystal Radio Design. Get Greater Sensitivity to very Weak Signals and Greater Volume, less Audio Distortion and Improved Selectivity for Strong Signals: 07/15/99;  02/12/06 
To maximize volume from headphones or a speaker, measure and use effective impedance. No lab test equipment is needed: 07/15/99;  06/21/03
Compare the impedance and sensitivity of headphones, earphones and/or speakers even if they differ greatly in impedance. No lab test equipment is needed: 07/15/99;  06/29/00
The best diode and audio transformer for a crystal radio, and a way to measure diode saturation current: 10/02/99;  08/22/02
Low-loss Impedance matching for magnetic and piezo-electric headphones, measurements on several audio transformers, and a transformer loss measurement method: 10/22/99;  03/30/08
A Crystal Radio Diode Detector Simulation using SPICE: 01/02/00;  11/23/01
Diode Voltage vs Current Curves:  Does an Actual Knee Voltage really Exist?: 01/08/00;  05/25/00
Crystal Radio Diode Detector Power Loss with Current with Voltage Waveforms, as Determined from a SPICE Simulation: 02/13/00;  11/25/01
Build the Diode Detector Bias Box: a simple and easy way to determine if one's diode is optimum for weak signal reception, or should have a higher or lower axis-crossing resistance (0.026*n/Is): 03/30/00;  01/24/07
A New Diode Detector Equivalent Circuit, with a Discussion of the Linear to Square Law Crossover Point: the signal level at which the detector is functioning midway between linear and square-law operation: 04/04/00;  10/27/2002
A Procedure for Measuring the Sensitivity (Insertion Power Loss), Selectivity and Input and Output Impedance of a Crystal Radio: 07/21/00;  04/10/2003
Directivity of the Inverted L Antenna with speculation as to why it Occurs and how it might be enhanced: 07/29/00;  11/20/2005
How to Measure the Electric to Acoustic Transduction Power Loss of Magnetic and Ceramic Earphone Elements, with Measurements of some Headphone Receiver Elements: 08/30/00;  10/28/2004
A Zero Loss, Unilateral 'Ideal' Audio Transformer Simulator plus... This device makes it very easy to determine the optimum audio transformer input and output resistances for any diode/headphone combination. No test equipment necessary: 01/05/01;  01/17/2010
Quantitative insights into Diode Detector Operation derived from Simulation in SPICE, and some Interesting new Equations relating diode SPICE parameters to weak signal sensitivity: 4/10/2001;  12/07/2008
A Procedure for Measuring the Saturation Current Is, and Ideality Factor n, of a Diode along with Measurements on various diodes: 03/28/01;  02/10/2004
New ways to Increase Diode Detector Sensitivity to Weak Signals, and a way to determine if a diode detector is operating above or below its linear-to-square-law crossover point: 04/10/01;  11/29/2006
Get 3 dB More Output for Greater Volume on Strong Stations plus...: 07/09/01;  04/06/07
An explanation of how the "Mystery Crystal Radio" works: 08/11/01;  12/29/02
How to Measure the Impedance of an AM Band Antenna-Ground System, what one can do with the results, along with some measurements: 11/24/01;  04/16/2004
Design, construction and measurement of a single-tuned crystal radio set using a two-value inductor, along with a discussion of the cause of 'hash', short-wave ghost-signal and spurious FM reception. A way is presented to determine if the signal operating the detector is above or below its linear-to-square-law crossover point: 02/07/2002;  08/20/2006
How to Make a Very Efficient Double-Tuned, Four-Band, MW Crystal Radio Set using two Version 'b' Single-Tuned, Four-Band, MW Crystal Sets 02/07/2002;  07/27/2002
Sensitivity and selectivity issues in crystal radio sets including diode problems; measurements of the Q of variable and fixed capacitors, RF loss in slide switches and loss tangent of various dielectrics: 03/25/2002;  06/10/2008
A new approach to amplifying the output of a crystal radio set, using energy extracted from the RF carrier to power a micro-power IC to drive headphones or a speaker: 07/04/2002;  02/25/2003
Highly sensitive and selective single-tuned four-band crystal radio set using a new contra wound dual-value inductor, and having a 'sharp selectivity setting'; along with a way to measure the unloaded Q of an L/C resonator: 02/10/2003;  10/23/2006
Measurement of the senstivity of a crystal radio set when tuned to a weak fixed signal, as a function of the parameters of the detector diode; including output measurements on 15 diodes: 08/14/2003;  08/19/2006
How to Reduce Diode Detector Weak-Signal Insertion Power Loss to Less than that Possible when the Input is Impedance Matched  Originally released as Article #15, later withdrawn  Republished as Article #28: 03/04/05
About Maximizing the Q of Solenoid Inductors that use Ferrite Rod Cores, including charts of Magnetic flux density and lines, with some actual Q and inductance measurements: 10/07/06, 01/07/08

This is an active page.  The content is updated periodically.

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First published: 10 Jul 1999;  Revised: 01/06/10