DELCO’s WONDERBAR automatic tuning system is one of the most fascinating technical features found in post-war American car radios. As early as the late 1940s, drivers could use it to automatically search for the next receivable radio station – decades before electronic station-seeking became commonplace.
The principle is surprisingly similar to that of a modern radio: the driver sets the desired reception sensitivity and then presses the large WONDERBAR button on the front of the radio.
The dial pointer then starts moving automatically from left to right across the frequency scale. As soon as the radio detects a station with sufficient signal strength, the search stops automatically.
HOW DOES THE WONDERBAR AUTOMATIC TUNING SYSTEM WORK?
Behind the automatic station search is not digital electronics, but a sophisticated interplay of mechanical components, spring force, gears, relays and a solenoid.
A tensioned spring provides the energy to move the tuner. Through a gear mechanism and a mechanical speed regulator, the tuner travels smoothly across the radio dial while the receiver electronics continuously monitor the signal strength. When a sufficiently strong station is detected, the electronics activate a relay and stop the mechanical search mechanism. The dial pointer remains precisely at the frequency that has been found.
AND WHAT HAPPENS AT THE END OF THE DIAL?
When the search reaches the right-hand end of the frequency scale, something particularly interesting happens: a powerful solenoid pulls the mechanism back to the beginning of the dial.
At the same time, the drive spring is tensioned again, allowing the search to start over from the beginning. In this way, the WONDERBAR essentially works as a fully electromechanical predecessor of today’s SEEK button.
A MECHANICAL MASTERPIECE
What a microprocessor accomplishes in a fraction of a second today was achieved in the WONDERBAR using gears, springs, electrical contacts, relays and electromagnets.
It is precisely this interplay of mechanics and electronics that makes these radios so fascinating today. The driver presses the WONDERBAR button, the dial pointer visibly starts moving across the scale and then stops almost as if by itself at the next radio station.
With a professional digital conversion, this original electromechanical automatic tuning system can even be preserved and continue to be used for station seeking – with modern reception technology working behind it.