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Comment by bjt2n3904 | Hacker News Reader

Not gonna lie. As a radio guy, our terminology is messed up. My favorite though is using superlatives.

Low Frequency (LF), Medium Frequency (MF), High Frequency (HF).

You'd think that maybe HF is WiFi, but you gotta remember these terms were invented back in the early days of radio. HF is between 3 and 30 MHz.

You have Very High Frequency and Ultra High Frequency, but that only takes us to 3 GHz. 5 GHz Wifi is technically SHF -- or Silly High Frequency.

But we also refer to these frequency bands in terms of MHz, or if we feel like it, wavelengths. Since radio signals travel (effectively) at the speed of light (m/s), we can multiply Hz (1/s) by a distance and get wavelength. (c = f * l). 144 MHz then is the 2 meter band, or VHF as we call it.

Confused yet? Wait until we start talking about baseband and I/Q signals!

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> 5 GHz Wifi is technically SHF -- or Silly High Frequency

For those curious, op's right and it actually is SHF, but it stands for Super High Frequency. I don't understand humour, only RF (and even that, barely).

https://en.wikipedia.org/wiki/Super_high_frequency

Here's a fun semi-relevant science experiment you can do at home: running a microwave will kill nearby wifi and bluetooth connections. Isn't that strange?

Try it with a par of bluetooth headphones right now!

I really don't know much about radio, but I have never experienced that the microwave have noticeably affected wifi or bluetooth.

Is it something that is only likely to happen with older and less isolated microwaves?

Yeah, modern microwaves shouldn't be leaking that much RF

Why wouldn't they leak RF? They aren't legally required to limit emissions at 2.4ghz.

is there any legal limit?

The FDA has one, but it's based on a maximum safe exposure to humans--which makes it fairly lenient.

> Why wouldn't they leak RF?

Customers might value using bluetooth and wifi. Not all pressures are regulatory!

Fair point.

Most people aren't using wifi near running microwaves, so it's hard to notice. Some microwaves leak more than others, but none of them are required by the fcc not to interfere with 2.4ghz wifi. The FCC says that they can actually leak an unlimited amount of radiation at that frequency [1], although obviously if it's high enough to start cooking people standing nearby other agencies than that the will get involved.

I bet ya an upvote that yours still leaks enough. One thing to try is to put your phone next to the microwave and place your bluetooth headphones or speaker riight at the limit of its range. Turn on the microwave and see what happens!

[1] https://www.ecfr.gov/cgi-bin/text-idx?SID=c7be03a4f7b02514ce...

I once worked at a site that had the Wi-Fi access point for one side of the office in the break room. There was, of course, a microwave in the break room. There were frequently complaints around the lunch hour that the Wi-Fi didn't work well, though strangely it worked earlier and later in the day.

My parents have an open layout house with the kitchen directly behind the living room. Because of this, it was always common to get up, walk and make some popcorn while watching a movie.

Once they started using netflix, this habit had to be broken quick.

I've found it varies a lot based on the microwave, distance (obviously) and positioning. My old apartment, anywhere in the kitchen and it'd kill my connection to my headphones. My new apartment (new appliances, too), I can be standing right in front of the microwave, and nothing.

> running a microwave will kill nearby wifi and bluetooth connections. Isn't that strange?

I replaced all of my light bulbs for bluetooth light bulbs.

Fun thing is that I can't turn on the light when the next door neighbors use their microwave. And by fun I mean dealbreaking.

Huh, my TV kept dropping the connection while streaming stuff from my computer downstairs. I wasn't using the microwave but maybe neighbors were... didn't consider this possibility. :D

> Confused yet?

No. It's basically defined relative to the audio spectrum.

Low begins at a point that is squarely out of the human hearing range: 30 kHz. That is just fast enough to start encoding intelligible speech into a carrier.

(Two decades that lie within audio range are called ultra-low and very-low.)

On the opposite end, the ITU acronyms now extend up to the 30-300 GHz decade, which is termed EHF.

https://web.archive.org/web/20131031020427/http://www.itu.in...

No, it is definitely not relative to audio. Sound waves and radio waves are of completely different carriers.

The reference medium frequency band in electromagnetic (EM) is based on the original AM broadcast frequency ranges (first time broadcasts could be separated into distinct frequency bands). Medium frequency (MF) is just what we started with broadcasts and the ranges expanded around that.

Audio and Radio frequency ranges are completely unrelated.

Radio is electromagnetic and audio is air pressure. As far as human hearing is concerned there is only one "band" 20 Hz to 20kHz with greatest sensitivity from 1kHz to 4kHz. That is air pressure wave propagation and has nothing to do with radio frequencies and propagation of electromagnetic waves in the ULF to VLF ranges.

> Sound waves and radio waves are of completely different carriers.

(ITYM "media"; a carrier is a waveform onto which a signal is imprinted.)

In an electronic circuit it's just frequency, whether the waveform came from a microphone, or from a radio-frequency oscillator.

When you mix audio into a carrier to produce a radio signal, it's all just math functions realized in the same medium: the medium of voltage/current changes versus time.

In radio, audio frequencies that were once carried through the air are imprinted, via electronics, onto radio frequencies.

For instance, a 500 Hz audio tone modulating a 700 kHz AM carrier creates 700.5 kHz and 699.5 kHz side bands (chopped to just one side band with SSB (single side band) encoding). The fact that there had been a sound wave moving through the air is now imprinted in the radio wave medium.

"Low frequency" in radio basically starts in a range that is outside of radio, yet high enough to be usable for carrying audio signals.

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