An Explanation of how the “Mystery Crystal Radio” Works

Quick summary Plans for a crystal radio called the “Mystery Crystal Set” were published in the newspaper “The Sunday Mail” of Brisbane, Australian in 1932. The “Mystery” in the name comes from the fact that, in the schematic, there seems to be no ground return to which the antenna currents can flow. The design was…

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

Part A: The Issues The sensitivity and selectivity in a crystal radio set can be impacted by many factors, including: A1: Ineffective coupling of the antenna to the tank circuit. A2: Resistive RF losses in the tank circuit. A3: Inappropriate diode. A4: Unintentional diode damage from exposure to electrostatic discharge (ESD) or voltages higher than the minimum reverse voltage…

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

Summary This article describes Version ‘c’ of a single-tuned four-band crystal radio set, sometimes called a “Venodyne” (constant bandwidth with maximum weak-signal sensitivity across the whole BC band, achieved by using 2 or more values of inductance in the tank – lower values at higher frequencies). It is designed for a constant bandwidth across the…

Measurement of the sensitivity 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

Summary This Article shows how the ‘weak signal’ power loss, from the resultant operation in the square-law region of the detector, of a crystal radio set, varies as a function of the parameters of the diode. The measurements clearly shown how ‘weak signal’ detector loss is reduced when diodes having lower values of the product…

About Maximizing the Q of solenoid inductors that use ferrite rod cores, including charts of magnetic flux density and flux lines, with some actual Q and inductance measurements from simulations in FEMM

Summary Many factors interact to affect the Q of ferrite rod cored inductors. Part one of this Article identifies and comments upon some of them. A simplified model and an equivalent circuit is also discussed. The second part describes several ferrite cored inductors, along with measurements of inductance and Q. The third part displays graphs…

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