I have used many times in the past diodes as unconventional RF detectors with great success, and sometimes, connecting the diodes to audio amplifiers many interesting things was heard. So after reading The Amazing All-Band Receiver, I decided to construct my permanent portable all band receiver.
I used a cheap pocket FM receiver and I removed all components from its PCB except those of the audio amplifier. In fact, all components from the volume potentiometer to the speaker were kept in place.
Then, I mounted this little schematic into a bit of prototype board, and placed it into the radio, connecting GND to GND, Vcc to the switched +3V, the output to the volume potentiometer and the small telescopic antenna to the antenna. Ugly but effective.
And the final result, looks like a common pocket radio:
What can be heard with this little radio? Everything:
- Placing it over the keyboard, I can heard the key scanning, and of course, the data sent to the computer when a key is pressed.
- Noise from many digital circuits can be easily heard, for example a desktop calculator machine or your computer's mouse.
- The multiplexing from LED displays can be heard also.
- You can heard also the noise from voltage converters , for example, all CCFL inverters.
- The noise produced by energy saving bulbs.
- Arcing from any defective neon tube can be heard without any problem.
- Moving it over a wall, you can find easily the mains wiring: A huge buzz mixed with many AM broadcast stations.
- Of course, any AM transmission in the nearby (CB, AM broadcast, ham radio...)
- Some strong FM stations can be heard if you look for a position with a direct and reflected signal coming simultaneously to your antenna.
- All devices working at 433 MHz can be heard without problems: Keychain remote controllers, remote units of meteorological stations... All ICM devices can be heard.
- Your local (analogic) TV station. The TV buzz mixed with the 15 kHz sync can be easily heard easily outdoors.
- Any GSM phone, working either at 900 or 1800 MHz band.
- Any GSM base station if you are near it.
- Wifi signals at 2.4 GHz can be heard if you are near a computer, laptop or wireless router moving data over the wifi link.
- Bluethooh signals can be also nicely heard.
- The microwave oven while heating you coffee.