SIGNALS AND COMMUNICATIONS

Electronic communications is exchanging signals. While these signals are symbolic in many communication schemes, they are almost exact electrical replicas of original information in analog wireless communications. Sound and vision are all such signals. Signals are converted into a form, by a transmitter, so that they can be transmitted in the air as part of electromagnetic spectrum, and are received by a receiver, where they are converted back to the original form. Two communicating parties can be quite far away from each other, and therefore the term telecommunications is used to describe this form of communications. What follows in this chapter is a descriptive theory of analog signal processing in communications.

Transceivers are wireless transmitters (TX) and receivers (RX) combined in a single instrument. This book is structured around building and testing a transceiver, TRC-10, operating in the 10-meter amateur band (28-29.7 MHz). The name is generic: TRC stands for transceiver and 10 indicate that it works in 10-meter band.

TRC-10 is an amplitude modulation superheterodyne transceiver. We have to make some definitions in order to understand what these terms mean.