Pocket FM radio receiver (schematic)

[zlatkoMM]

Pocket FM radio

Is anyone see this small weirdo before?
Design is very unusual and when i have i will try to build one.
I think that will work also with BF566 VHF pnp transistor.
-------------------------------------------------------------------------
Original text:
------------------------------------------------------------------------
This is the most simple fm radio receiver with good performances that works

great even if the sensitivity is not too high. The working principle of this fm

receiver may seem a little unusual. It is made of an oscillator (T2 and T3) that

is synchronized with the received frequency of T1. This transistor works as a

broadband preamplifier in VHF range.

The oscillator is adjusted between 87 … 108 MHz with C5. Because of the

synchronization, the oscillator output will have the same frequency deviation as

the received signal from the fm antenna. This deviations are caused by the

broadcasted audio informations. The frequency modulated signal show up on P1 +

R5. Low pass filter R6/C6 extracts the audio signal and then is amplifier by T4

… T6 and transmitted at the output through C9 capacitor.
FM Receiver Circuit Diagram


The coil details are presented in the fm receiver circuit diagram. The radio

receiver is adjusted on different stations with the help of C5. P1 potentiometer

is adjusted untill the best reception is obtained. If we attach an audio

amplifier and a speaker then this fm receiver can be made very compact as a

pocket radio.

 

[betwixt]

Re: Pocket FM radio

Interesting!

The component references are not on the schematic but I think I can see what is going on.

I think it uses a zero, or close to zero IF by running the oscillator very close to the signal frequency then uses a pulse counting detector to recover the audio. A similar design was available commercially in the UK back in the 1970s. Performance isn't great but it should work. I haven't simulated it but my intuition says the oscillator may not run without some more components though.

Brian.