Roberts radios and the completed AM to FM radio converter

As featured in the British Vintage Wireless Society Bulletin Vol 42 - Summer 2017 magazine.

Owing to a fast decline of medium waveband broadcasts and a continuing interest with vintage AM radios, Guy Fernando (M0OOX) presents this cost effective design for enabling FM broadcast stations to be listened to on classic vintage AM radios.

AM broadcasts in the United Kingdom and the rest of the world are in rapid decline and are likely to cease altogether by the middle of the 2020s, mainly due to higher transmitter running costs and dwindling listeners. Many countries in Europe have already closed AM broadcasts completely. Here in the UK on the long wave band (148.5 - 283.5kHz) only BBC Radio 4 can be heard. On the medium wave band (526.5 - 1606.5kHz) there remain a few regional and commercial stations that can be heard, but the only nationally covered stations are BBC Radio 4, and Radio 5 Live. It is however a different story on the FM band (87.5 - 108.0MHz). At least for the foreseeable future, there remains a wider selection of FM stations including regional, community and the national BBC stations, Radio 1, Radio 2, Radio 3 and Radio 4 FM.

It is feared, with the imminent closure of the AM band countless vintage radios will become aesthetic curios or worse end up in skips - FM to AM converter to the rescue! These types of converters were widespread in the 1960s and 70s and sold mainly as AM car radio adapters, but have now disappeared into obscurity and the few that are still being manufactured are fairly costly owing to the niche market at which they are pitched. It is hoped this simple converter design described here will offer a new lease of life to AM only radios without breaking the bank.


Building the FM to AM Radio Converter

The converter is simple to build and should not pose any problem to the seasoned constructor. There are two ways to build the converter. It is offered as a kit, comprising of a professionally manufactured printed circuit board (PCB), with pre-programmed PIC, and all the other components to enable you to build a working converter. Alternatively just the pre-programmed PIC is available for constructors that choose to build their own converter on stripboard.

Further useful information regarding project may be found at UK Vintage Radio Repair and Restoration forum.

Schematic diagram of the FM to AM converter

Full design details for both build methods are presented below.




Board Layout

When completed it should look something like this.

PCB layout of the FM to AM converter



Parts List

The kit comes complete with the following main components to build a working converter. Please note that a suitable enclosure with battery compartment and wire must be sourced separately.

Reference Description
R1 470kΩ ¼W resistor
R2 1kΩ ¼W resistor
R3 120kΩ ¼W resistor
C1 100nF capacitor
C2 56pF capacitor
C3 2.2nF capacitor
C4 270pF capacitor
C5 220pF capacitor
C6 100pF capacitor
C7 150pF capacitor
VC1 3-30pF variable trimmer capacitor
L1 150uH inductor
L2 1mH inductor
Q1 2N3904 NPN transistor
U1 Pre-programmed PIC12F1572 microcontroller
U2 RDA5807M FM receiver module
BTN1 12mm x 12mm momentary tactile push button
PCB Printed Circuit Board
Button Cap Button cap for button
IC Socket 8-pin low profile DIP socket

The kit may be purchased below.

Buy the Kit for the FM to AM Radio Converter


FM to AM Radio Converter Kit

 


Board Layout

When completed it should look something like this.

Stripboard layout of the FM to AM converter



Parts List

The stripboard build requires the following main components to build a working converter. Please note that all parts except for the PIC must be sourced separately.

Reference Description
R1 470kΩ ¼W resistor
R2 1kΩ ¼W resistor
R3 120kΩ ¼W resistor
C1 100nF capacitor
C2 56pF capacitor
C3 2.2nF capacitor
C4 270pF capacitor
C5 220pF capacitor
C6 100pF capacitor
C7 150pF capacitor
VC1 3-30pF variable trimmer capacitor
L1 150uH inductor
L2 1mH inductor
Q1 BC184L NPN transistor
U1 Pre-programmed PIC12F1572 microcontroller
U2 RDA5807M FM receiver module
BTN1 12mm x 12mm momentary tactile push button
Stripboard 10 x 34 holes, 0.1" pitch
Button Cap Button cap for button
IC Socket 8-pin low profile DIP socket

The pre-programmed PIC microcontroller may be purchased below.

Buy the PIC for the FM to AM Radio Converter


PCB for the FM to AM Radio Converter

 

Delivery is via the Royal Mail Track and Trace service.


Happy listening!