building a simple FM receiver

[mdanh2002]

Hi,

I am thinking of building a simple FM receiver following the circuit on this website **broken link removed**

I have most of the components available, except for L2 (22uH RF Choke). Can I wind it myself in the same way as winding an inductor? i have built various FM transmitters and usually hand-winding works well.

If I cannot do it myself, can I use the resistor-like inductors instead? There are so many for cheap prices on ebay. Btw, is the value critical?

Alternatively I have a few old broken radios, can I possibly salvage it from the existing circuit?

Any advice is appreciated. Thanks.

 

[colin55]

L2 is not critical. Just wind 100 turns of 0.1mm wire on a 1M resistor.

 

[mdanh2002]

Thanks. So RF choke is not purely inductor, but has resistance as well? Is there any formula to calculate the inductance of such a coil based on the number of turns? I only have 0.3mm wire and it's not enameled also the turn has to be spaced apart.

 

[transistor495]

This radio won't give you a clear output. It distorts. I made one before.

 

[audioguru]

The "radio" has extremely poor performance:
1) It is overloaded by strong local stations and is not sensitive to weak distant stations. Each station will have different volume.
2) It has an AM detector but detects distorted FM if you tune it to one side of an FM station.
3) Its AM detector picks up lots of static interference.
4) Its squelch oscillator beats with the stereo pilot and stereo subcarrier of an FM radio station causing all kinds of noises.
5) It causes radio interference to nearby FM radios.

The same author made a a real FM stereo radio with a TEA5711 IC made by Philips but the IC is not made anymore.

 

[colin55]

0.3mm coil with spaces would be absolutely enormous.

 

[ronv]

Use the resistor looking ones. Might find some in your radios.

 

[wkrug]

Are you searching for such a Part?
L-HBCC 22

 

[mdanh2002]

Thanks all for the advice. I am thinking of buying L2 22uH from ebay. Must I specifically buy those items labeled as 'RF Choke' or can I just buy the normal 22 uH inductor instead? From the pictures, both of them look similar.

As for the quality, it doesn't matter to me. This is meant for fun and as long as I can get a talking voice coming from an FM station from my circuit, I am happy.

 

[transistor495]

The difficulty is to get the transistor oscillated and quenched at the same time. The quench waveform samples the received signals in an AM way according to the frequency deviation - that you demodulate and output. It is not continuous samples. This concept adds the distortion.

You need to place the RF components closely on a pcb and use the specified components, else it won't work. Also be ready to experiment on the tuning capacitor and associated cap values to get on to the broadcast band range when you hear a static through the speaker.

 

[mdanh2002]

Thanks, I will hand wire L2 instead, try it out and post again when I got it working.