[dvh]

Another trick is not to use constant RPM because you can hit some mechanical resonance point, but constantly varying RPM around target RPM so that the system even if it hits resonance stays there only for a brief moment and won't start vibrating.

[thebruce87m]

They do the same with clock signals in some systems. Similar idea to avoid high peaks at a single frequency:

> Spread spectrum clocking is a technique used in electronics design to intentionally modulate the ideal position of the clock edge such that the resulting signal’s spectrum is “spread”, around the ideal frequency of the clock. In timing circuits, this has the advantage of reducing Electromagnetic Interference (EMI) associated with the fundamental frequency of the signal.

https://www.microsemi.com/document-portal/doc_view/135439-wh...

[immibis]

This is controversial, because the same amount of noise is emitted, just with a different shape that is still able to be picked up by radio receivers just as well, but is more likely to pass regulatory tests.

[mlyle]

We have a standard for the maximum energy on given frequencies, not the total EM emitted. Spread spectrum clocking definitely reduces the peak energy on specific frequencies, which is usually what you care about more.

I guess it makes you more likely to experience interference, but the interference you'll experience, on average, will be much less severe.

[immibis]

No radio receives exactly a single frequency. They all receive a range.

[mlyle]

Sure--- I'm familiar with the bandwidth theorem. In general, a single narrow carrier with lots of energy inside your channel is more harmful to demodulators than spreading the interference over 20MHz, most of which isn't even on top of your channel (or, if your channels are reaaaaaallly wide, it's still just a slightly increased noise floor instead of a strong single frequency swamping your signal).

I've designed a lot of radio systems, built a lot of demodulators, and calculated a lot of link budgets. It's best to assume that people know a fair bit, here, instead of tossing out the simplistic dismissal.

I'm also an amateur radio operator, and I know that strong carriers are often far worse for me down in HF than the same energy spread out over tens of thousands of cycles; though I can often notch carriers, I only have so much dynamic range.

[tliltocatl]

Offtopic: constantly varying RPM across a resonance point might not be a good idea, it was exactly what blew up Sayano-Shushenskaya Dam.

[jayd16]

I that worse than accidentally landing on it?