# How do i make a radio?

1. Jul 21, 2004

### Phymath

How would u make a radio thats tuned into 120.55 Mhz? or any frequency? I thought you would fallow this formula...
(120.55 * 10^6 Hz) = 1/(2 pi sqrt(LC)), where L is the inductence, and C the capacitor. well i figured a 1 micro (10^-6) Henry inductor and a 1.743 pF (10^-12) would create the resonance frequency of 120.55 Mhz and thus that radio station would come in on the sieres circut i created, but would this acutally work? what would be the actually schematic where to place the anntenna, ground, diode, head phones, etc.. thanks to anyone who can explain to me if or how it will work

-Phymath

2. Jul 21, 2004

### RFbeginner

I've seen that

One of my instructors showed us a simple AM radio he built with just that type of setup. It was a totally passive radio. A simple antenna lead to a tank circuit... the tank circuit was in parallel to another parallel branch that had a diode and capacitive earphone (single earphone).

3. Jul 21, 2004

### rayjohn01

Why 120.55 Mhz is there at strong station there , and if so is it AM or FM .
The type of circuit your refering to is the simplest form of AM radio. It comprises a parallel tuned circuit using a cap of say 20 pf ( usually a variable ) with suitable inductor per your calc. of good Q . They used to wind them . The antenna ( wire of several feet )is connected to one end of the // pair and a ground "large metal chassis'
to the other. A diode is connected from the antenna side to some earphones and then back to ground. The earphones should be coil types NOT capacitive.
This circuit is NOT very sensitive and used to be used for longwave radio reception at 500Khz or so. It will not receive FM stations .
If your really serious you may wish to look at some modern chips which can be the basis of very sensitive circuits , but they require a fair amount of support components.
Ray.

4. Aug 12, 2004

### Ingyil

Hi.
What RFbeginner told U is a good project, I made once this type. U don't have to use power sources or batt's, only a big antenna, an earphone (like the old phones), and creativity making the inductance. It works better if you use a mobile indictance inside the first one.
Bye.

5. Aug 12, 2004

### chroot

Staff Emeritus
These sorts of passive radios are called "crystal radios," by the way, and the web is teeming with info about them.

- Warren