What is Going On with 2.4GHz Spectrum?

by | Oct 1, 2020 | Blog

2.4GHz spectrum has been around for decades.

Some refer to it as the “garbage band” – Keith walks through the different parts of the spectrum to see what’s really going on.

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Welcome

My name is Keith Parsons

In today's little video

we're going to talk about 2.4 GHz spectrum

what's going on?

This is the spectrum that's been around

for a couple of decades now

for a long time it was called the

garbage band and I don't know

if we want to consider it the garbage band today

but it's been around a long time

and done a lot of things

Today in this little video

we're going to talk about what's going on

what are some of the wireless networking protocols

we're using in this band

Let's just look and think through wavelength

size and frequencies we have available to us

you can see in the front line

up at the top

under wavelength

wavelength is just the

speed of light divided by the frequency

well we know the frequencies 2.4 GHz

it's actually a very tightly defined 2.4 412

is the center frequency of Channel 1

but what does it look like in size

if we want to see the size

we can look and see that 2.4 GHz

is about 12.5 cm about

it depends on whether you're on the left side

or the right side of the form

or if you want to think of an inch

is about 4.9 inches

so we have a little router there you can look at

but if we're going to compare 2.4 to 5GHz

and now what's available in 6GHz

you can see 2.4GHz only has about 80 MHz of bandwidth

very small

and we only have like three channels we can choose from then

so as we went from 2.4 to 5

we got a lot more space

and then moving to six is even more

Now, at the bottom of the page

you can see there's

80 MHz of channel and there's a formula

2407 times 5 plus the channel number

is going to end up giving you what you're looking for

if that's the specific frequency

you're looking at

and the wavelengths go from about 2.5 cm

all the way up to down

because we're going up the sides going down

down to about 12 cm

So let's look at these

I've broken down through a couple of different ways

that we can zoom in and see these

In 802.11b

we used 22 MHz wide channels

when we move to 802.11g/n/ax

sorry, there's no ac in 2.4 gig

we use only a 20 MHz wide channel for OFDM

Now if we look at those

there's Channel 1 and a Guard Band

Channel 6 and a Guard Band

and in between every channel is a Guard Band

the job of the Guard Band is to make sure that people

on one channel are listening to people

on the other channel

now when they first released this

they didn't know where in the world

this is going to be released

so they said we want to have 2 MHz channel

3 MHz Guard Band and as long as you do that

you can use anything you want

and so different countries came up with different things

in the U.S. we happened to go through 1 through 11

but other countries use different channels

it doesn't matter what country you live in

it still works out that we only have three channels

that are not overlapping

yes, you can use those other channels

the problem is that causes something called

adjacent channel interference

which is far worse for a Wi-Fi than

co-channel interference or co-channel contention

when you're on the same one

Now if you're in some places in the world

where you have channels 1 through 13

it's possible to run a four channel plan

it works, I've used it

the problem is if there's any one on Channel 6

you're getting adjacent channel on both sides

of Channel 6 and you get a lot more harm

so if you can get away with only using those four

great

the problem is I haven't been in very many places

where they have no neighbors who

might be on something else

well we also have here Zigbee and

Zigbee uses a different channel plan

that uses them differently

they're further spaced apart

and in the graphic you can see they have

a different central frequency

and then BLE and Bluetooth

if you look at the bottom

have a whole bunch of little teeny channels

and they're doing a frequency hopping

where they're doing jump, jump, jump

hopping back and forth between those

all the channels are available

in the BLE there's a couple of them that are

kind of poking up a little bit and you might

see these in a spectrum analysis

if you ever use a spec an in 2.4 gig

these are the channels that are

I don't use the word beacon

because beacon actually means

something else in BLE

but they're transmitting a lot to give a local point

where devices can hone in on and say

I know exactly where I am and then be competitive

so you should see and you will see

where BLE is prevalent

these little spikings that are coming up

in your channels

So 2.4 gig

80 MHz for the channel

three channels for Wi-Fi

More for Zigbee and BLE has a whole bunch of them

depending on whether you doing

direct spread spectrum

frequency spread spectrum

again these are useful

we're going to be using them

but they're actually pretty crowded right now

as long as we're talking quiet

we may be able to get them to work

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