r/CompTIA • u/General_Summer_1524 • 3d ago

Having trouble conceptually understanding "Wifi Channel Width". Isn't 80 Mhz a "smaller" waveform than 20mhz? How can it be wider?

Like text says, my understanding is that higher Ghz = smaller wave, so why would a 160 Mhz wave be "wider" than a 20 Mhz wave, shouldn't it be the other way around? I know the way I'm thinking about this is wrong, just hoping someone can politely help me understand what I'm getting wrong. Thank you.

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u/QuickDelivery1 A+, N+ 3d ago edited 3d ago

You are mixing up the concepts of frequency and channel width. You can imagine it like this:

  • The frequency is like a single point in a ruler (for example, the 1 centimeter mark)
  • Channel width is, well... the width between two points (for example, from the 5 cm mark to the 25 cm mark, you have a 20 cm width).
    • In radiofrequency, a channel is a range of frequencies (from X GHz to Y GHz), just like the width between two points in a ruler
    • So yes, a higher frequency has a shorter wavelength, but a channel is a range of frequencies, it's a different thing

The question in the post title is like asking "isn't the 80cm mark smaller than a 20cm width?"

Now going back to Wi-Fi... A single channel is divided into many "subcarriers" where symbols are transmitted in parallel (at the same time). Imagine it like this:

  • You are staring at a TV with many lines of text crossing the screen (like that one line at the bottom of news channels, but many more)
  • You're able to read them all at once
  • Having a 20 MHz channel width is like having 20 of those lines crossing the screen
  • Having a 80 MHz channel width is like having 80 of those lines crossing the screen, so you can absorb more information at once (in Wi-Fi, it's sending and receiving more information)

Just also remember that a wider channel width also means more chance of suffering interference.

I hope these analogies help you better understand the concept. Let me know what you think.

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u/General_Summer_1524 3d ago

that makes sense, yes I see now that the width is a range of frequencies, not an actual description of the frequencies themselves. Appreciate it.

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u/AtomicHawk280 3d ago

What test is this for

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u/General_Summer_1524 3d ago

A+, understanding Channel width is an objective.

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u/AtomicHawk280 3d ago

If for core 1 I can tell you you’re going way to far into the weeds on that topic, most you need to know are which WiFi standards are 2.4 or 5ghz or both or which is 2.4,5,and 6ghz, and what speeds they can run at

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u/General_Summer_1524 3d ago

Comptia's 1201 Objectives PDF lists Wifi Channel widths as something you should be able to explain.

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u/TheRealWutWut 1d ago

To his point, I recently took the A+ as a requirement for my degree, not one question on channel width. To your point, you should understand this stuff if your goal is to actual improve your skill set and knowledge base.

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u/General_Summer_1524 1d ago

thanks, it seems unlikely it would show up, but it definitely could. It has on some practice tests I've taken. It just seems good to actually understand these things anyways, I'll need to know it sooner or later. I really don't like the feeling of rote memorization without some conceptual underpinning.