radio transmissions at the frequency of light

Radio waves at the frequency of light *is* light.

Nope. The antenna size is about the diameter of an atom. The best antenna *is* an atom.

Yup. Laser.

John

Its very easy to do, just modulate a led or laser, and you have an AM transmitter, and if you whish it, also a very narrow transmission beam. Also, a choice of transmission frequencies is available, from infrared to UV lasers.

There are also designs that use cavity or transmission-line resonators. These work at frequencies too low for lasers and masers, although they get a bit bulky below UHF.

The lowest imaginable frequency is the one for which the universe (assuming that spacetime is closed; the jury is still out) is a resonant cavity.

I couldn't figure out whether he was asking that in reference to radio light frequencies, or if it was just a general question.

Obviously one can live without coils in a transmitter, even where they'd otherwise be the norm. But, you'd either end up with a lousy transmitter, or one that is pretty low powered.

For instance, one could use crystals or ceramic resonators (or even ceramic filters) as frequency selective elements, but they sure aren't useable at high power levels. And if you put them before the output stage, then you risk issuing spurious signals generated in that later or those later stages.

A power crystal oscillator isn't completely uncommon, but again they tended to put a coil in the output. If you can live with instability, or a low enough frequency, and lots of harmonics, the power oscillator could be controlled by a resistor and capacitor, basically a multivibrator, and thus live without coils. But I'd not want to try to listen near that transmitter, and it wouldn't be long before some regulator official came knocking to complain.

Michael

A spinning magnet is a radio transmitter.

John

There no problems.

Signalling using light is a well established technology.

Graham

like a laser?

Bye. Jasen

Such as in a laser listening device. How about fiber optics.

modulate a led or laser,

Really? Where does the electric field component come from?

Bob M.

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Not true. I can imagine one for a universe twice as large as ours.

Boy, I sure can't. Try as I might, I just can't imagine one much bigger than about 1.75 times ours...:)

Bob M.

The movement of the magnetic field, of course. You just haven't heard them because nobody yet knows how to spin a magnet at 33,000,000 RPM. ;-)

Without coils, that is. ;-)

Cheers! Rich

What's kewl is to imagine a universe that's actually infinite, so the lowest freq. is DC.

Of course, then we're left with the polarity question. ;-)

Cheers! Rich

. 1) Use a bulb or an LED or laser.

2) A 'coil' can be anything tha has inductance including, for example, a short strip of copper on a circuit board a few millimetres or even a few microns long. That is why leads are kept so short and components small, in very high frequency equipment.

3) Yes: A magnetron does not have 'coils' in the conventional sense. It generates microwave energy in an oscillatory chamber within an intense magnetic field.

BTW are these answers for a test or exam?

Isn't that around 1.2 GHz.?

Hi, this might be of interest:

Huh? Got a universe in your pocket? ;-)

Given the size of the "known" universe, about 12,000,000,000 light- years, the frequency at which it's a resonant cavity would be, lessee, say a full-wave cavity, just for the sake of discussion,

12,000,000,000 lightyears = 1.13526341 × 10e26 meters so at 300,000,000 m/sec, that'd give you, um... 2.642558523047968224e-18 Hz.

Cheers! Rich

Sure, doesn't everyone? I was probably thinking of the big-bang noise. Or maybe I wasn't uhhhhhhhh.......

Don

Why did I just hear "...or are you just happy to see me?" after that? ;-)

Bob M.