Receivers: From Spark to 16-Qam

This online engineering PDH course covers the development of radio receivers from the late 1800s to the present, simultaneously in separate dimensions: Time and Frequency.  As communications technology has progressed since the late 1800s, so has the upper frequency limit. The advancement of technology and upper frequency have happened in parallel so organizing this course in chronological order dovetails well with increasing frequencies.While circuitry is not addressed except in a very few cases where it cannot be avoided, there is extensive information to cover the evolution of radio receivers.

In the last few decades, incredible advances in computer technology have led to the ability to digitize received signals for computer processing.  This brings tremendous advantages, as adding software capabilities does not require hardware changes.  For example, a receiver can be configured with a wide selection of filter bandwidths to allow matching the filter to the incoming signal.  Such a system would be unaffordable in hardware. As analog-to-digital conversion becomes possible at ever higher frequencies, the conversion point has been migrating closer and closer to the antenna.

We are now in the era of the software-defined-radio.  Regardless, the physics of the universe still applies, and the techniques developed over the last century are still relevant, even if incorporated into a computer program. George Santayana warned that those who ignore history are doomed to repeat it.  While he did not have the evolution of communications gear in mind, his rule applies here too.