FM to AM Radio Converter

Easy to build electronic construction project for receiving FM broadcasts on vintage AM radios.

Written by Guy Fernando

Last modified November 2020


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. The PIC microcontroller is available pre-programmed to avoid the inconvenience of having to program it. All other components including the RDA5807M FM receiver module can easily be found online.

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

Schematic diagram of the FM to AM converter

There are two ways to build the converter. It may either be build on a professionally manufactured printed circuit board (PCB), or laid out manually on stripboard (veroboard). Note that for transistor Q1, a 2N3904 is used for the PCB version, and a BC184L is used for the stripboard version, these transistors having different pin outs.

Full design details for both build methods are presented below.




Board Layout

PCB layout of the FM to AM converter

Parts List


Reference Description
R1 470kΩ ¼W
R2 1kΩ ¼W
R3 120kΩ ¼W
C1 100nF
C2 56pF
C3 2.2nF
C4, C5 220pF
C6 100pF
C7 150pF
VC1 3-30pF variable trimmer
L1 150uH
L2 1mH
Q1 2N3904 NPN transistor
U1 PIC12F1572 microcontroller
U2 RDA5807M FM receiver module
BTN1 12mm x 12mm momentary tactile push button

Download the full PDF article (PCB build)

Buying the pre-programmed PIC and PCB

If you would like to build this project, a pre-programmed PIC12F1572 microcontroller together with a professionally manufactured printed circuit board (PCB) may be purchased here. Please note that all other parts for the project must be sourced separately.

FM to AM Radio Converter - Buy the PIC and PCB


PIC + PCB for the FM to AM Radio Converter

 


Board Layout

Stripboard layout of the FM to AM converter

Parts List


Reference Description
R1 470kΩ ¼W
R2 1kΩ ¼W
R3 120kΩ ¼W
C1 100nF
C2 56pF
C3 2.2nF
C4, C5 220pF
C6 100pF
C7 150pF
VC1 3-30pF variable trimmer
L1 150uH
L2 1mH
Q1 BC184L NPN transistor
U1 PIC12F1572 microcontroller
U2 RDA5807M FM receiver module
BUTTON1 12mm x 12mm momentary tactile push button

Download the full PDF article (Stripboard build)

Buying the pre-programmed PIC

If you would like to build this project using stripboard, a pre-programmed PIC12F1572 microcontroller may be purchased here. Please note that all other parts for the project must be sourced separately.

FM to AM Radio Converter - Buy the PIC


PCB for the FM to AM Radio Converter

 

The price includes postage and packing via "Royal Mail Signed For" service, delivered to either mainland UK or Worldwide.


Happy listening!