Asimov wrote:

Hi,

I am thinking out loud about how the semiconductor LED evolved into
the laser diode, by exploiting the synchronized population increase
mechanism to generate monochromatic photon emission. Might it be
possible to scale down this electron mechanism to usable radio
frequencies and end up with a radio transmitting antenna that doesn't
require aerials? Might this device then be termed a radio diode?

LEDs don't emit coherent radiation. All your jumbo "RED" would do would
be to emit wideband noise.

--

Peter

They don't? Then hell--I am throwing this laser led away!!!

John

"Peter Hayes" wrote in message
o.uk...
LEDs don't emit coherent radiation. All your jumbo "RED" would do would
be to emit wideband noise.

It's not THAT wide, is it? Anyone know the Q of an LED? I'd guess it's at
least 10...

I have a high-power LED flashlight, 5 superbright leds in the element... it
is bright, if I bring it near an AM radios I lose all reception... this rfi
is solely the product of the leds, the connecting wires and the
batteries--the flashlight housing is aluminum...
I have never checked just how large a bandwidth the rfi covers...

Regards,
John

Your flashlight likely has a DC-DC converter in it to keep the light
output relatively constant as the battery voltage drops. That would be
the source of the RFI. It's also possible that the LEDs are multiplexed
so that one won't hog all the current as they would if parallel
connected. That also could create considerable RFI. Although the RFI is
radiating from the components you mention, they aren't its source.

Roy Lewallen, W7EL

John Smith wrote:
I have a high-power LED flashlight, 5 superbright leds in the element... it
is bright, if I bring it near an AM radios I lose all reception... this rfi
is solely the product of the leds, the connecting wires and the
batteries--the flashlight housing is aluminum...
I have never checked just how large a bandwidth the rfi covers...

Regards,
John

Well, you might be right at that (and contrary to how you took my posts--I
DO recognize you as an authority which has been around the block many more
times than I), however, I have had that flashlight apart a half-dozen times,
at least, it cannot be found!

But, it is quite possible the current limiter is right on the chip with the
LEDS and potted with it in the LED lenses... all five LEDS run in
parallel....


Warmest regards,
John

Now, that got my attention. I haven't kept up well with LED technology,
but I haven't heard of any LEDs that have a built-in regulator,
switching or otherwise. Out of curiosity, I tested the LED lights I have
with an AM radio, and found the following:

1. A three-LED headlamp with no obvious electronics, fixed intensity,
runs from 3 AAA cells: Quiet, no RFI.
2. Two different LED headlamps, one with 3 and the other 4 LEDs, with
several intensity settings, run from 3 AAA cells: Loud audio whine.
3. Two small UV LED lights, run from 3 button cells: Quiet, no RFI.
4. Newly purchased one-LED flashlight, runs from a single AA cell:
Generates an RF hiss.

This is about what I expected. The #2 headlamps switch the lights on and
off with varying duty cycle to get the different intensities. This can
be seen by rapidly moving the light while on. The switching isn't
visible at the maximum brightness setting but apparently the switcher is
still on. It might be doubling as a regulator. High intensity LEDs seem
to require about 4.5 volts for full brightness, and one cell is nowhere
near enough to light one up without a DC-DC converter. So the #4 light
has to have one. That explains its RFI. Built-in converters seem to be
getting more common; without one, batteries last an incredible length of
time, but at the expense of light intensity that falls dramatically as
the battery discharges, especially during the first part of the
discharge period.

So unless there's some sort of LED defect that can cause RF noise, my
money's still on your having some kind of converter or switch hidden in
your flashlight somewhere. All the lights I have which don't have either
are quiet.

Roy Lewallen, W7EL

John Smith wrote:
Well, you might be right at that (and contrary to how you took my posts--I
DO recognize you as an authority which has been around the block many more
times than I), however, I have had that flashlight apart a half-dozen times,
at least, it cannot be found!

But, it is quite possible the current limiter is right on the chip with the
LEDS and potted with it in the LED lenses... all five LEDS run in
parallel....


Warmest regards,
John

On Fri, 29 Apr 2005 02:43:31 -0700, Roy Lewallen
wrote:


There is a letter on this very subject in the Pease Porridge column of
the latest issue of "Electronic Design."

Now, that got my attention. I haven't kept up well with LED technology,
but I haven't heard of any LEDs that have a built-in regulator,
switching or otherwise. Out of curiosity, I tested the LED lights I have
with an AM radio, and found the following:

1. A three-LED headlamp with no obvious electronics, fixed intensity,
runs from 3 AAA cells: Quiet, no RFI.
2. Two different LED headlamps, one with 3 and the other 4 LEDs, with
several intensity settings, run from 3 AAA cells: Loud audio whine.
3. Two small UV LED lights, run from 3 button cells: Quiet, no RFI.
4. Newly purchased one-LED flashlight, runs from a single AA cell:
Generates an RF hiss.

This is about what I expected. The #2 headlamps switch the lights on and
off with varying duty cycle to get the different intensities. This can
be seen by rapidly moving the light while on. The switching isn't
visible at the maximum brightness setting but apparently the switcher is
still on. It might be doubling as a regulator. High intensity LEDs seem
to require about 4.5 volts for full brightness, and one cell is nowhere
near enough to light one up without a DC-DC converter. So the #4 light
has to have one. That explains its RFI. Built-in converters seem to be
getting more common; without one, batteries last an incredible length of
time, but at the expense of light intensity that falls dramatically as
the battery discharges, especially during the first part of the
discharge period.

So unless there's some sort of LED defect that can cause RF noise, my
money's still on your having some kind of converter or switch hidden in
your flashlight somewhere. All the lights I have which don't have either
are quiet.

Roy Lewallen, W7EL

John Smith wrote:
Well, you might be right at that (and contrary to how you took my posts--I
DO recognize you as an authority which has been around the block many more
times than I), however, I have had that flashlight apart a half-dozen times,
at least, it cannot be found!

But, it is quite possible the current limiter is right on the chip with the
LEDS and potted with it in the LED lenses... all five LEDS run in
parallel....


Warmest regards,
John

On Fri, 29 Apr 2005 02:43:31 -0700, Roy Lewallen
wrote:

I haven't kept up well with LED technology,
but I haven't heard of any LEDs that have a built-in regulator,
switching or otherwise.

Hi Roy,

Constant current LEDs have been around since the late 70s. They were
marginally common then, but I rarely see them now.

As for the spectrum of LEDs, the all require different battery
voltages to bring them to full output. Light power is always
expressed as a function of current, not voltage however. The voltage
is somewhat likened to the forward conduction knee.

IR LEDs have the lowest knee voltage, roughly at the same potential as
common diodes: 0.6V. Blue LEDs have the highest knee voltage, roughly
3V to 3.5V. The colors Red, Orange, Yellow, Green, Aquamarine, Blue,
UV exhibit the order of ascending voltage (and in the conventional
order of wavelength for a rainbow). The White LED is simply a Blue or
UV LED coated with phosphor (a solid state fluorescent light).

73's
Richard Clark, KB7QHC

John Smith wrote:
"I have a high power LED flashlight. 5 superbright LED`s in the
element...it is bright. If I bring it near an AM radio, I lose all
reception."

I have a Timex Indeglow watch with a fairly dim dial illumination when I
depress the dialstem. It wipes out radio reception too. I suspect that
solidstate diodes are noidy devices. They are efficient though as the
light is not accompanied with much heat. As for diode noise, zeners are
often used as noise generators, are they not?

There are various ways to get an atom`s orbital electrons to move to a
higher energy level. You can throw a stick on a fire or aim an electron
beam on a CRT phospher.. From a laser, we`re looking for coherent
radiation.

Best regards, Richard Harrison, KB5WZI