Solid State Shortwave Receivers For Beginners - The Listeners Guide

Crystal Set
CHAPTER 2
Ultra Simple Receivers
A good starting point for anyone interested in building receivers
is to build a crystal set. The main advantage of this type of set is its
extreme simplicity. Another very important one is that they require
no power supply and have no running costs. This tends to give crystal
sets an added fascination over other types of receiver as it is actually
the power of the received transmission that provides the energy that
drives the diaphragm of the headphones or earpiece. It may seem
impossible that the energy radiated from a transmitter some hundreds
or even thousands of miles away can provide sufficient power to
produce an acceptable volume at the transducer of the receiver, but
indeed it can.
Before considering a practical crystal set circuit it is a good idea
to look at what the received signal is actually like.
High frequency A.C. signals at the transmitter are radiated as a
form of electro-magnetic signal which is usually termed radio waves.
These travel out from the transmitter at the speed of light (186,000
miles per second) and when they reach a receiving aerial they generate
minute electrical signals in that aerial. These signals are identical to the
original high frequency A.C. signal produced at the transmitter, but are
of course at a very much lower power level.
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