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Frequency response of IR LEDs

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TheVictim

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Some of the datasheets I've seen for IR LEDs do not indicate a frequency response. I have transmitted audio using them, but do not really know how high of frequency I can use.

What is typical for IR LEDs, and are there any that are specifically for high frequency applications. I'd like to achieve 100mhz if that is possible.
 
IR LEDs are pretty fast. Photo-transistors are very slow.
Photo-diodes are faster than photo-transistors but are slower than IR LEDs.

You will be able to communicate at a few hundred kHz if you use a photo-diode, not anywhere near 100Mhz.
 
Deep sixes that idea. Perhaps I'm asking the wrong question. If I want to transmit and receive an analog IR signal around 100Mhz how should I go about it? What about using a fibre optic receiver?
 
OK, but I'm gonna catch some flak from this...


This is an experiment to improve the traditional but really poorly performing laser microphone.

1) Modulate an IR source (preferably a laser) at 100Mhz

2) Bounce the beam off an audio source, which will cause FM modulation due to Doppler shift (in theory)

3) Receive the reflected beam. Inject the signal into an ordinary FM radio at 100Mhz and let the radio due to work of demodulation and producing audio.
 
A laser microphone picks up the vibrations from a window or the glass covering a photograph, doesn't it? They vibrate poorly so that is why they perform poorly. Modulating the beam at 100MHz (if it works) will sound exactly the same, very poor.
 
That's the idea behind the experiment, but I don't want it to fail because the components can't handle the required frequency.

What can I use?
 
TheVictim said:
That's the idea behind the experiment, but I don't want it to fail because the components can't handle the required frequency.

What can I use?
To prove that glass makes a lousy microphone then shine an unmodulated laser beam on a window or on the glass of a photograph and receive it with a photo-transistor or photo-diode. It won't be FM it will be AM because the reflected beam changes its intensity with the vibrations of sound.

Then try it again with the beam modulated with 100khz and detect FM from it with a CD4046 phase-locked-loop.
 
The easiest way to improve sound quality is to simple pass it through an appropriate equalizer. The higher sensativity you can get on reception the better your ability to adjust the very non-linear frequency responce you'd get from various physical sources of audio, you basically have to map the objects acoustical properties. The radio won't do the work because it's expecting a relatively linear audio response.

https://en.wikipedia.org/wiki/RONJA#Nebulus_infrared_LED_driver

They use IR LED's for modulation of 16mhz signals. Obviously the shallower the depth of modulation and the higher the sensativity of the receiver the better signal you'll have to work with, but 100mhz would be an intersting feat, and as everyone is saying, it's not really going to give you any advantage. Laser mics are limited mostly by the object they're pointed at.
 
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