In 1989 radios still had single channel bespoke crystals to generate their channels. We moved on to phase locked loop technology rapidly from then. 

Circuit boards were populated with through hole components to a single printed trace on the reverse of the board.. It was necessary in most cases to “hard wire” the channels in a radio.

The next step change was the micro processor, making much of the radio’s functionality programmable. Currently, manufacturers use a multi-layer trace, and surface mounted components enabling higher component density leading to small feature rich, software programmable radios we have today.

AM FM & Digital Modes Originally, AM was the only mode for radios to modulate the transmitted signal. In subsequent years, FM became the mode of choice.

Narrow band FM has advantages over AM in terms of it’s reduction in interference and being able to use non linear amplifier stages in the radio. Modern advances in signal processing have made possible digital modulation enabling radios to send the modulation as pulses and packets of data.

This means clear and consistent communication even when the signal is poor, it does however have a point where the signal disappears completely. Digital modes have standards which are used widely and are either frequency or time division multiplex.