Foxhole radio help

[7Coline]

http://imageshack.us/photo/my-images/72/dscf0321im.jpg/
4 cm diameter pvc tube
~120 spirals
blued razor
blue wire goes to 50 m antenna
red wire goes to ground
black wire goes to piezoelectric disk

Hello guys ,

I have tried to make an foxhole radio, but with no luck .
I get nothing in the piezo disk . I need some help to figure out what went wrong here .

Thanx in advance.

[5B4AJB]

You probably need some oxide (rust) on the razor, since modern razors are stainless.

Otherwise, everything looks good.

If you want to see if the rest of the circuit is actually working, replace the razor/pencil (detector) with any diode.

You may need a transformer before the headphones, this helps the volume.

I've made a few crystal radios which work on the same principle, but using a crystal as the detector.

[K7KBN]

My experiences with crystal radios forces me to ask what the impedance of the earphone is that you're using. These circuits generally need something of pretty high impedance - 2000 ohms was a pretty common value a few decades ago, and crystal headphones had even higher Z. A modern earphone might load the circuit down as badly as a dead short.

[techiesteve]

When I built crystal sets as a boy I used 2000 or 4000 ohm SG Brown headphones. Wish I'd saved them now, they'd be useful for a retro regenerative RX I'd like to build.

[K7KBN]

I don't know about military surplus availability in GB, but now and then I find US Navy (and sometimes Air Force) flight helmets from the Vietnam era. Great stuff; nominally 2K ohms and a 300-3000 Hertz response. Wunnerful stuff! Of course, the helmet covers up little things like the wife announcing that dinner is ready -- things like that ---

[5B4AJB]

The old style rotary telephones have suitably high impedance earpieces.

Looking at your circuit again, I notice you have no (variable) capacitor, strictly speaking, you don't need one, but adding one in parallel with the inductor will give you a far greater tuning range.