Is It Possible to Convert an AM Radio to an FM Radio Without Replacement?

The electronic circuit design to perform this task is quite different. You cannot easily modify an AM radio to receive FM by simply swapping a few parts. Re-engineering the electronic circuit would be a much more time-consuming effort than simply replacing the entire chassis.

General Approach: Mistuning the Receiver

In general, an AM radio can receive FM signals in the same frequency range by slightly mistuning the receiver, a technique called "slope detection". For instance, if a receiver is designed to work in the 1 MHz AM broadcast band, it can be "converted" to work at 100 MHz by the FM broadcast band. However, this method only works with older, possibly dismantlable devices. Most modern receivers do not have scavengeable parts that can be repurposed in this way.

Tweaking an AM Radio to Receive NBFM FM Signals

Theoretically, broadcast AM uses a widely different frequency band from broadcast FM. If you are particularly interested in converting a very old AM CB radio to receive NBFM (Narrow Band FM) narrow band FM CB signals, it might be possible to tweak the radio for this purpose. However, the quality of the reception might not be optimal because FM detection typically uses a limiter before the frequency discriminator, which the off-tune circuit used for slope detection would lack to filter out amplitude variations in the FM carrier.

Potential Solutions and Further Exploration

For a more in-depth understanding, one could delve into the principles of radio and electronic signal processing. Radio hams and enthusiasts often explore these topics, and there are numerous resources available both in books and online. If you are involved in radio, you are already familiar with the complexities involved in signal modulation and demodulation. However, for the general public, it might be easier to understand these concepts through educational software and applications, such as GNU Radio, which can help in learning how a radio’s signal processing works.

The short answer is 'no'—broadcast AM uses a distinctly different frequency band than broadcast FM. It would be both challenging and potentially less effective to attempt to convert an AM radio to an FM radio without purchasing a new one or undertaking extensive modifications. Given that many contemporary radios are software-defined, using an application like GNU Radio could be a more practical and educational approach.