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.
I know this a very old post, but I'm very interested in making this so cute receiver. Would have some more information on the polarized capacitor value for instance? And what is the type of the other capas? Cheers
Use something in the 1 - 10 uF for the polarized capacitor. For the other capacitors I used ceramic ones. Good luck with your receiver!Delete
Can I use Germanium diode or Schottky rectifier diode?ReplyDelete
Yes, but sensitivity will sufferDelete
Can I connect crystal earpiece directly to the circuit without amplifier?
Probably yes, but you need a lot of gain to be able to hear signals in ambient street noise so an amplifier will be needed anywayDelete
I bulit this circuit today, and it works. I used BC639 and GA206 Germanium diode ( all components salvaged from old circuit boards ) + piezo buzzer as crystal earpiece. When I am using this device, I hear lots types of sounds so it works good, but I also hear AM station even with 1 meter antenna so my question is :
Is that because I am using germanium diodes, or AM station transmitting, because I live 24 kilometers from it and the transmitter power is
200kW, and the last question is: does the maximal receiving frequency depends on diode, or transition frequency of the transistor.
PS: I like your circuit version more, than from site www.techlib.com, and sorry for my bad english, because I am from Czech Republic.
If you live near an AM broadcast transmitter you will hear it constantly with any diode. The only cure is to reduce the antenna length or reduce the input capacitor (which will favor higher frequencies) or install some kind of high band pass filter.Delete
The maximum frequency is determined by the diode: the transistor only amplify the recovered audio.