BladeRF-wiphy: Open-source, software defined radio modem

Radio passing through radio doesn't interfere with thr signal. Its just more likely that the interfering signal will also be picked up by a receiver.

Think about a bright white lighbulb next to a small red LED; you won't be able to see the small LED.

The other part is that out eyes are essentially 2d grids that are fairly large in both directions with respect to thr wavelength of light. Radio receivers are essentially a single point.

We can also bend and focus light with lenses fairly easily with many different substances, due to the refraction index of the material.

If you move the red LED away, you will be able to see it more easily. This is because we can focus the light onto more than just a point receiver so that the the bright light doesn't entirely overwhelm all the sensors. If you do photography, you know that overexposure is problematic and can cause areas around bright areas to be overexposed as well.

While we cant use glass to bend radio waves, they can be be bent in the same way as visible light. Ham radio operators do this all the time by using the ionosphere to bounce radio off of to make long distance contacts that are beyond normal line-of-sight.

Radio and visible waves are also subject to gravitational lensing.

They are also both subject to diffraction, where the light will bend slightly around the endge of an object. Ham radio operators also make use of this to make contacts near the edge of obstructions, like mountains.

Visible light can be used in fiber-optic cables, and waveguides are a similar device used for microwave-frequency light.

> Why can’t they make visible light with an antenna?

In terms of normal radio antenna designs, you could, I think, but antennas need to be sized proportional to the wave length of the light.

However, since visible light is higher energy than radio light, and near many of the transition energy found in atoms, we make extensive use of that additional energy when detecting (e.g. photoreceptors in our eyes and photodiodes), emitting (e.g. LEDs and incadescence), and using (e.g. photo etching and film photography) visible light.

> Why are large arrays of RF receivers not more widely used for small-scale RF imaging?

You can only image something down to a resolution of the wavelength used.

You do see some applications of this, viz millimeter wave imaging at airports.

I can't find the link, but a week or some ago, there was an article on hackernews about radio imaging of cities from satellites? If I find it I'll edit it in. Resolution on the order of meters is adequate for that purpose. (For reference: WiFi is roughly 12½cm. Fm radio stations are roughly 3m. Am radio is roughly 300m.)

Also, this is a limitation of visible light microscopes as well. We can't imagine, say, molecules, because theyre smaller than the wavelengths of visible light.

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One of the biggest difference between visible light and radio light when it comes to thinking about propogation is what absorbs it. Your WiFi router can be on the otherside of a wooden wall because wood doesn't absorb or reflect substantial amounts of rf energy; a metal wall does. 5ghz doesn't propogate as well as 2.4 because it's absorbed by water in the air and things more than 2.4ghz is. Visible light is absorbed by most things some amount.

So, the big differences are how the physical world affects the light, but in broad strokes it behaves the same way to the same situations, its just that those situations (e.g. what can reflect, refract, diffract, and absorb it) are frequency/wavelength dependent.

Why can't an oscillator and antenna emit matter? Is some matter transparent to other matter in the same way that some matter is transparent to light? This idea that matter and energy are equivalent and that the same wave physics underlies it all doesn't seem to be true in reality. Instead it seems that phenomena are divided into regimes and in each regime behavior is very different. Sure it's tough to build an oscillator at the frequency of matter, but is it really impossible to build a matter emitter? I only have a BA in physics but I remember while learning (and in later reviews of physics) that it seems like theory doesn't always scale and there are a lot of very weird assumptions and "explanations".

You can. The antennae are the size of molecules. LEDs emit light, your retinas receive them. The retinal dye molecules are tuned for specific frequencies just like you'd tune a macroscopic antenna.