Light from antena?

N

[email protected]

Jan 1, 1970
0
If light is part of the same spectrum and waveform as radio waves and
radio waves can be transmitted through an antena then couldn't visible
light? If a sine wave driver was adjusted to run in the visible
spectrum and then connected to an earth ground and needle point antena,
could visible light be seen coming of off the needle point?

J

John Fields

Jan 1, 1970
0
If light is part of the same spectrum and waveform as radio waves and
radio waves can be transmitted through an antena then couldn't visible
light? If a sine wave driver was adjusted to run in the visible
spectrum and then connected to an earth ground and needle point antena,
could visible light be seen coming of off the needle point?

N

[email protected]

Jan 1, 1970
0
Around the antena? By the way, has this ever been tried before?

N

Nick Funk

Jan 1, 1970
0
I believe it is called a light bulb!

A

Anthony Fremont

Jan 1, 1970
0
"John Fields"
Considering just the antenna, calculate the length of a 1/4 wave
whip at far infrared.

I recommend using a "generic" isotropic point radiator for best results.
;-)

J

Jamie

Jan 1, 1970
0
If light is part of the same spectrum and waveform as radio waves and
radio waves can be transmitted through an antena then couldn't visible
light? If a sine wave driver was adjusted to run in the visible
spectrum and then connected to an earth ground and needle point antena,
could visible light be seen coming of off the needle point?
i would like to see the set up capable of emitting that spectrum!
but to answer you question, you would see light but only at the
initial take off point and normally with in the first wave length or
half wave length..
i am taking this from memory while in school many years ago and
back then it was just more theory on some parts of the instructors
since the thought of generating RF at the wave length was far fetched!
don't remember all of the physics behind it but i seem to remember
that you should see only a surface glow effect due lost and wave length
space.

D

Don Klipstein

Jan 1, 1970
0
If light is part of the same spectrum and waveform as radio waves and
radio waves can be transmitted through an antena then couldn't visible
light? If a sine wave driver was adjusted to run in the visible
spectrum and then connected to an earth ground and needle point antena,
could visible light be seen coming of off the needle point?

You would need a sinewave oscillator of frequency in the 428-750
terahertz range. A halfwave dipole would have a length of .2 to .35
micrometer. If you want to make an oscillator along the line of a Hartley
or a Colpitts or an Armstrong, you need an inductor wound with a wire a
fraction of a wavelength long (less than .2-.35 micrometer), and all other
parts much smaller still - submicroscopic.

As for semiconductors that oscillate at such frequecies nowadays: We
have laser diodes.

A halfwave dipole antenna in a laser beam will produce a sinewave
electrical signal - but have fun finding a way to detect AC at frequencies
that high, or building an antenna too small to see with any ordinary
microscope!

- Don Klipstein ([email protected])

D

Dr Engelbert Buxbaum

Jan 1, 1970
0
If light is part of the same spectrum and waveform as radio waves and
radio waves can be transmitted through an antena then couldn't visible
light? If a sine wave driver was adjusted to run in the visible
spectrum and then connected to an earth ground and needle point antena,
could visible light be seen coming of off the needle point?

The basic idea is sound, but consider that FM radio has a wavelength of
several meters, long wave radio of several km. That makes building
antennas (which have 1/4 or 1/2 of that length) relatively
straightforward. Wavelength for visible light is 400--700 nm, light
antennas are therefore a subject of nano-technology.

E

Eric R Snow

Jan 1, 1970
0
The basic idea is sound, but consider that FM radio has a wavelength of
several meters, long wave radio of several km. That makes building
antennas (which have 1/4 or 1/2 of that length) relatively
straightforward. Wavelength for visible light is 400--700 nm, light
antennas are therefore a subject of nano-technology.
Why antennas made that are 1/4 or 1/2 the wave length? Is it because
the energy emitted is a sine wave? Or am I totally off base. I'm just
curious and have little electrical knowledge.
Eric

D

Don Bruder

Jan 1, 1970
0
Eric R Snow said:
Why antennas made that are 1/4 or 1/2 the wave length? Is it because
the energy emitted is a sine wave? Or am I totally off base. I'm just
curious and have little electrical knowledge.
Eric

A quarter or half-wave antenna can send/receive the tuned frequency just
fine, in literally half or a quarter the space of a full-wave antenna
for that frequency. Which, in the case of low frequencies, might
renamed "Project ELF" (for "Extremely Low Frequency") and the plans they
had for turning a strip of Michigan's upper penninsula into an
ultra-jumbo antenna for talking to the nuke subs back in the 70s.)

R

Rich Grise

Jan 1, 1970
0
I believe it is called a light bulb!
Actually, it's not. It's a different mechanism.

What you really need is an atom-sized klystron! ;-)

Cheers!
Rich

D

Don Klipstein

Jan 1, 1970
0
Why antennas made that are 1/4 or 1/2 the wave length? Is it because
the energy emitted is a sine wave? Or am I totally off base. I'm just
curious and have little electrical knowledge.

of the "ARRL Handbook" and the "ARRL Antenna Book".
ARRL stands for "Amateur Radio Relay League", and editions of these
books 50 or probably more years old remain valid in this area. Antenna
theory known as of WWII covers this.

- Don Klipstein ([email protected])

M

Michael A. Terrell

Jan 1, 1970
0
Don said:
of the "ARRL Handbook" and the "ARRL Antenna Book".
ARRL stands for "Amateur Radio Relay League", and editions of these
books 50 or probably more years old remain valid in this area. Antenna
theory known as of WWII covers this.

No, it doesn't. ARRL stands for "American Radio Relay League". I
have a copy right here by my desk.

--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida

B

Bob Myers

Jan 1, 1970
0
Eric R Snow said:
Why antennas made that are 1/4 or 1/2 the wave length?

A short-form, somewhat-simplified explanation is as follows:

Consider what happens on a quarter-wave long length of transmission
line, open at the far end. Or better, at multiples of a quarter-wavelength
back from the open end on such a line. The "standing wave"
pattern on such a line, resulting from the total reflection of the
forward signal by the "open," has a voltage maximum (and
obviously, a current minimum) at the open end, and conversely
a voltage minimum (and current maximum) at a quarter-wavelength
back (with this pattern repeating from there).

Now, think about a half-wavelength antenna - a simple "dipole"
- as being nothing more than such a quarter-wave section of
line, "opened up" such that one conductor points this-a-way and
the other conductor points that-a-way (in the opposite direction).
Our first guess might be that the standing-wave situation described
above remains in effect - the tips of this "opened-up" structure are
points of high voltage (and opposite polarity, with respect to one
another), while the center is a low-voltage/high-current (read: low
impedance) point. This is precisely what you want for making EM
radiation - an electric field created "across" the structure (i.e., between
the
high-potential ends), plus a magnetic field created "around" it and in the
correct phase relationship. So what we've just described ought to be just
fine for launching EM radiation, while providing a reasonably decent
impedance at the point we wish to drive (the center of the structure).
So, with at least very minimal math, this is a workable model or
visualization as to why half-wave dipoles work well for transmitting
radio waves. (And fortunately, what works well for sending such
signals works just as well for receiving them.)

A quarter-wave antenna results from noting that the two pieces of
the above structure are really just quarter-wave-long mirror
images of one another, and either of them will work in the same
manner if the other is replaced by a "ground plane" normal to the
remaining element and passing through the center point of the original
dipole structure. This plane, from the standpoint of determining the
fields produced by the remaining element, really DOES act like a
"mirror," although obviously nothing is really emitted by the "mirror
image" viewed as being on the other side of that plane.

In reality, various factors make for neither the half-wave dipole or
the quarter-wave derived from it exactly a half- or quarter-wave
long, relative to the wavelength of the signal in question in free
space. They're generally going to turn out being a bit shorter, to get
the proper "resonance" and a decent (resistive only, in the ideal case)
feedpoint impedance. But they're close enough that these names
work just fine.

Bob M.

B

Bill Bowden

Jan 1, 1970
0
Why antennas made that are 1/4 or 1/2 the wave length?

It's a natural length that works best without extra parts.
Shorter antennas less than 1/4 wavelength are sometimes
used where the antenna needs to operate at different frequencies.
But they need to be tuned with extra inductors and capacitors
to keep the whole arrangement resonant at whatever frequency
is used.

The basic idea is to make the antenna look like a resistor
to the transmitter, and a 1/4 wavelength looks pretty close to 50 ohms
without extra parts.

Think about it. If the transmitter is connected to a resistor,
all the energy is converted to heat. Now if you connect
the transmitter to an antenna that acts the same as a resistor,
and the antenna doesn't get hot, the energy must have
gone out into space, which is what you want to do.

But, if the antenna is not the right length, and looks like a
capacitor or inductor, the energy will flow back a forth between
the transmitter and antenna and probably make the transmitter
hot, and not radiate much energy, other than heat.

-Bill

E

Eric R Snow

Jan 1, 1970
0
of the "ARRL Handbook" and the "ARRL Antenna Book".
ARRL stands for "Amateur Radio Relay League", and editions of these
books 50 or probably more years old remain valid in this area. Antenna
theory known as of WWII covers this.

- Don Klipstein ([email protected])
Thanks Don,
I'm going on vacation and will try to get those books before I leave.
Cheers,
Eric

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