I read the wikipedia article but I still can’t wrap my mind around it.
https://en.wikipedia.org/wiki/Rusty_bolt_effect
In: Engineering
Basically, the design of radio hardware (antennas, connectors, cables, etc.) assumes that you have nice metal that behaves “properly” in an electrical sense…it’s a good clean pure low resistance.
If you have parts of the metal that aren’t in good condition, like a rusty bolt or a corroded connection or something else that screws with the conductivity or resistance, you can get interference in the radio signal.
A very rough analogy is a water pipe. A good pipe is nice and smooth and the same diameter all along. Water flows nice and smooth and steady. Rusty bolt effect is like putting cracks and joints and rough spots (and possibly rusty bolts!) inside the pipe…the flow isn’t as smooth. You’ll get turbulence.
If you’re a musician, a tube instrument like a trombone or flute is a better analogy, since that’s also a resonator like a radio antenna. Even a tiny pinhole in the instrument body can cause squeaks and octave jumps and other interference with the main signal.
You know how when an incident wave runs into a region with higher impedance, you get a reflection?
That happens a little bit when a radio wave runs into metal (good conductor), and it happens more when a radio wave runs into a layer of oxide (poor conductor). If you have an object that’s covered with little dots of rust, or a rough-textured surface made partly of rust, all the contours of that rust produce ‘echoes’ that interfere with the original signal. It’s a little bit like a wave passing through water, and then it runs into patches where the water has a different resistance – like it’s Jell-O instead of water. As the wave ran into those denser regions it would distort and bounce around.
There’s no ELI5 for this. I’d have to study this for 20 years just to be able to ELI40 this.
Antennas transform a wire-bound electromagnetic signal into an unbound one that radiates away in space.
This works by having a certain impedance, caused by the geometry of the antenna and its material properties. One of these material properties, and the much important one I guess, is the surface conductivity, e.g. the electric resistance of the material. If it is off a bit, the overall impedance of the antenna changes, which alters their electromagnetic cross-section in space and alters their effective frequency band. Rust, or more precise oxidation, changes the surface material chemically which has drawbacks on resistance.
This isn’t a problem with broad band antennas, but it has quite an impact on highly frequency-selective systems, such as radio telescopes or aviation-navigation equipment.
As described in the Wiki article, corrosion causes dissimilar materials to be in contact, which can create a rectifier. In other words, a really crappy diode. (This is how metal tooth fillings can sometimes pick up AM radio!)
A diode will mess up a radio wave’s waveform. An ideal diode will just remove the negative portion; a crappy diode will cause other distortions too. But let’s just cover the ideal diode.
If you remove the negative portion of a sine wave, you create an abrupt transition at every point that it crosses the time axis (x axis). Abrupt transitions make unwanted noise. If you do a Fourier analysis of such a waveform, you’ll find that the result is a bunch of new high frequency components added in. That’s the only way to recreate a half cycle waveform out of sine waves. (A Fourier transform tells you how to construct a waveform using just sine or cosine waves.) Those new unwanted harmonics can mess up your signal transmission.
And that’s just an ideal diode. Your crappy rectifier makes other artifacts as well, putting more junk in the signal.
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