Crystal_radio_with_impedance_matching.svg
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Summary
Description Crystal radio with impedance matching.svg |
English:
A
crystal radio receiver
circuit that uses
impedance matching
to increase the power transferred from the antenna through the receiver to the earphone
E1
. This type of circuit was used in higher quality radios around 1920. Maximum power is transferred from one circuit to another when their
impedance
(resistance) is equal. However, in a crystal receiver, the impedance of the antenna-ground circuit (around 10-200 ohms) is far less than the impedance of the tuned circuit
(L1, C1)
(thousands of ohms at resonance) and varies depending on the length of the antenna, etc.. Therefore the antenna is connected to a tap across only a portion of the coil's turns, using a multiposition switch,
S1
. This makes the tuning coil
L1
act as an impedance matching autotransformer in addition to its tuning function, transforming the high impedance of the tuned circuit down by the square root of the turns ratio to match the antenna. The switch
S1
is adjusted until the radio station is loudest in the earphone.
The impedance of the crystal detector
D1
is also matched to the tuned circuit by connecting the detector, like the antenna, to a tap on the coil. In addition to improving power transfer, impedance matching also improves selectivity of the receiver (its ability to reject interfering signals at nearby frequencies) by reducing the resistive "loading" of the tuned circuit, increasing the
Q factor
.
|
Date | |
Source | Own work |
Author | Chetvorno |
SVG development
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Licensing
I, Chetvorno , the author of this drawing, release it into the public domain for any use whatever
Public domain Public domain false false |
I, the copyright holder of this work, release this work into the
public domain
. This applies worldwide.
In some countries this may not be legally possible; if so: I grant anyone the right to use this work for any purpose , without any conditions, unless such conditions are required by law. |