Wifi 802.11n- Max Speed 144Mbps in 2.4Ghz

<< I kindly want to find why MAC does no accept 40Mhz from modem. >>

that works ONLY if yours is the ONLY Router using 2.4 GHz in your 'Network Neighborhood'. if you live in a detached house far away from neighbors, you might be able to use it all. but if anyone nearby wants to use any channel in 2.4 GHz, its will clobber your data.

a SCAN will also tell you whether there are other Routers nearby using that 2.4 GHz band.

RSSI of -50 says you are very close to your Router. -40 is about the best I have seen.

-75 is unusably bad.

Consider running an Ethernet cable and obtaining an adapter for speeds of up to 1,000 M bits/sec

Noise of -87 suggest that there is interference from other Routers, baby monitors, microwave ovens, portable landline phones or other devices on your channel.

Transmit Rate of 144 M bits/sec is a fast as you can go wth that modulation method using your NSS = 2 antennas. Your hardware appears to be operating normally.

Why did you not connect on the much faster 5GHz band? is it shut off at the Router?

The next level we can use is to use the SCAN tool in Wireless Diagnostics to look around at what is visible over the air around the Mac. This has the advantage of showing what is seen at the Mac, which may be slightly different than what is seen at the Router(s).

this is what it looks like:

(drag and drop on Preview to see larger, or make your own)

Click on the channel column to sort by channel. This tells you the nominal channel in use, but every channel also spreads up and down the channel numbers, depending in its channel width. For example, channel 36 at 80 MHz wide spreads to engulf everything up to channel 48. You may need to look up the spectrum spread with some tables, available online. Or post back here and readers can look those up for you.

your Mac should selectively connect to either 2.4 GHz or 5 GHz, whichever seems to be able to produce a faster connection. in the 5 GHz band your Router can set channel-width wider and attain higher speeds, even if you are limited to 802.11n.

what is puzzling is that your Mac did not connect to 5 GHz, presuming it is available.

Wireless diagnostics:

By far the easiest way to cause poor performance, instability, overheating and crashing is to install ANY third-party speeder-uppers, Cleaners, Optimizers, or Virus scanners, Bit Torrent, or a VPN that you installed yourself.

¿Are you running anything like that?

Wireless diagnostics:

Hold down the Option key while you click on the Wi-Fi icon on the menubar to open up the tools for investigating and fixing Wi-Fi issues

First is "Open Wireless diagnostics", which opens the wireless diagnostics Assistant, but does not proceed.

There are about eight different things you can do from here, but the top-level is to choose Diagnostics off the Window menu, or simply click continue, to do a quick check for Gross misconfiguration or operating problems. Your Admin password will be required. If any recommendations are shown, you should consider then seriously.

Next is to hold down the Option key and click the Wi-Fi icon as before. The screen that opens shows operating parameters of your network. Screenshot, transcribe, or photograph the results and post back in a reply on the forums. Looks like this older one.

...

mahmut_aydin_ wrote:

I already said modem does not support 5Ghz.

If this is ISP-provided Wi-Fi equipment, contact them and ask about getting it replaced with something newer.

There are three non-overlapping channels available in most 2.4 GHz networks, and they tend to be clogged.

mahmut_aydin_ wrote:

I am considered if there is neighbor who is using 2.4Ghz; why windows is tolerating it and windows use 40Mhz to support 300mbps

You forgot the part about your router being outdated, exceedingly insecure, and quite possibly part of a botnet.

A botnet that will clobber your network bandwidth.

And a compromise that may well be collecting your own Internet and internal network traffic, as well.

you have connected in the 5GHz band, on an 80 MHz wide connection on channel 44 using 802.11ac rules.

unfortunately, you are so far away from the Router, you have raw signal RSSI of only -72 dB, where -75 is completely unusable, and around -40 is right next to the Router.

if you can decrease the distance between the Router and computer, your speed should improve. Top speeds on that band with two antennas is 866 M bits/sec.

what speeds do you get right near the Router?

802.11n is an older spec that operates only on 2.4GHz.

802.11ac is newer and operates on 5GHz.

You are probably seeing the difference due to the band each is operating on. It's also possible that your 2.4GHz channel 6 has contention from other nearby WiFi access points, which would reduce speed. Your 5GHz ac connection is on a completely different channel somewhere between 32-177. 5GHz is typically faster than 2.4GHz although it has a shorter range.

Your M3/MBP supports 802.11ax, successor to ac. Try connecting your M3/MBP to the 5GHz channel on your modem.

mahmut_aydin_ wrote:

Actually, 802.11n supports 2.4Ghz and 5Ghz.

Also, my modem supports 802.11n, not support ac (newer). I am sure that windows is connected by 2.4Ghz with 802.11.n

Technically 802.11n support on 5GHz is optional , it doesn't guarantee that every device supports it on 5GHz, especially older devices. Check the specs on your modem to see if it supports n on 5GHz.

a 40 MHz wide channel in in 2.4 GHZ band takes over the entire band, and when actively sending data, can knock other nearby Routers off the air. This is not a practical solution unless you live far away from any other neighbors. Your noise numbers -87 suggest is not the case. A SCAN would tell you for certain.

What’s the router vendor and model here?

Is this ISP-provided gear, or yours?

Why Windows uses the entire 40 MHz slot (all of 2.4 GHz) is a question best asked of Microsoft. (It wouldn’t surprise me to find that configuration gets lower performance in many Wi-Fi network conditions, too.)

If you want Apple to add (802.11n and later) 40 MHz slots in 2.4 GHz, send them feedback: Product Feedback - Apple

Why not use all of 2.4 GHz? Nobody here can answer the “why?” questions. Only Microsoft and Apple.

That Zyxel VMG3313-B10A router is being actively exploited by at least one major botnet (qv CVE-2024-40890, CVE-2024-40891, and CVE-2025-0890), so who knows what that router is really doing right now:

https://www.techtarget.com/searchSecurity/news/366618782/Zyxel-wont-patch-end-of-life-routers-against-zero-day-attacks

https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-command-injection-and-insecure-default-credentials-vulnerabilities-in-certain-legacy-dsl-cpe-02-04-2025

Get it replaced.