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Radio-emitting LEDs?

  1. Dec 23, 2009 #1
    As the title may suggest, I am in search of a LED that emits radio waves. Yes, radio. I have seen and heard of the wide spectrum of waves LEDs can produce, ranging from ultraviolet to infrared LEDs, but never of anything beyond that, for say, radio waves. Of course, it may sound as stupid as asking for a lamp emitting gamma ray on the shorter side, but this is practically possible, for so I believe.

    Also, I want to ask, do radio phototransistors exist?
  2. jcsd
  3. Dec 23, 2009 #2
    The wavelength of visible light is between 380 nm and 760 nm, while radio is as much as two or three orders higher, depending on the frequency. You would need an LED a few centimeters to several meters wide. There are also other impracticalities I'm sure others can point out.
    Last edited: Dec 23, 2009
  4. Dec 23, 2009 #3
    There are Gunn diodes - when placed in a resonating cavity, they will emit microwaves if you apply DC voltage.

    otherwise diodes can be used to multiply radio waves,

    Any reasonable transistor responds to radio waves. It can amplify, generate, or multiply radio waves among many things.
  5. Dec 23, 2009 #4
    "Also, I want to ask, do radio phototransistors exist?"
    I think he was talking about using the radio signal as the gate for a transistor, like how visible/UV/infrared light is used in photodiodes and phototransistors, rather than simply amplifying a radio signal.
    Last edited: Dec 23, 2009
  6. Dec 23, 2009 #5
    The magnetron in a microwave IS a radio emitting diode, and a very powerful one at that
  7. Dec 24, 2009 #6
    As weird as it seems, there are several two terminal devices that can produce radio waves or even be used to amplify them!. My favorite of these is the Tunnel or Esaki diode. I had great fun playing with one of these in college ;)
    Essentially, if you supply a current to it, the diode will reach a point where the voltage across it begins to decrease as the current increases. That is the definition of a negative resistance. That is,
    R = V/I, but in this case, R < 0, because the slope of V/I is down.
    Anyway, you can place a parallel tuned circuit across it and as long as it isn't loaded to heavily, it will oscillate.
    Now, what's even MORE interesting than that is that someone discovered that a similar diode can be fabricated from parts found in an era 1900 barn!
    It thrills me to no end to know that Hertz could, if he'd known this, have constructed a CW transmitter.
    Anyway, there's also the aforementioned Gunn diode which is commonly used in speed radar guns. Just put them in a can, apply voltage through a bit of inductance and off they go, singing like they had no better sense.

    There's also some crazy powerful transmitter diodes, like the IMPATT and TRAPITT diodes.
    Last edited by a moderator: Apr 24, 2017
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