Regarding 802.11n and throughput

I was wondering something.

Why my throughput on N is between 20 to 30mbps? even though the "link speed" is 300mbps.

During speed testing, I see to much variance on the download (the graph is all over the place), meanwhile the upload looks steady (I'm using local nearby servers, so wired test do show max speed).

What could be a source of disturbance for the signal even if the AP is actually in the same room as the client?

I have tried changing the channel, signal strength. Do not know what else? Is for general wifi on any router make and model, not specific answer needed, just the basic stuff to look for.

2.4ghz is plagued by interference from about everything. Bottom line - wifi 4 is slow, use 5ghz wifi 5 if you want speed.

Theoretical world: 300 mbps is a theoretical PHY rate achieved with 40mhz channels and 2x2 MIMO. With normal wifi overhead in a perfect radio clean room standing right next to the router with perfectly compatible client + router you’ll probably get real speed of ~200mbps.

Real world: Most clients will connect either 1x1 or 2x2 on a 20mhz channel. That will get you max throughput of ~50-100mbps. That number will decrease the more interference you have - neighbors, baby monitors, Bluetooth devices, heavy traffic, microwaves, etc.

Good article on PHY, overhead, and wifi 4:

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