i've been searching but couldn't find a proper answer for my issue, sorry in advance if it's somewhere i didn't reach!
so, i have this:
Model: TP-Link TL-WR740N/ND v4 (specs: 1 WAN + 4 LAN, all 100 Mbps / Wireless N, 1 antenna)
Architecture: Atheros AR9330 rev 1
Firmware Version: OpenWrt 18.06.9 r8077-7cbbab7246 / LuCI openwrt-18.06 branch (git-20.319.49209-ab22243) (the latest i can use with this model, if i'm not mistaken)
i'm using it as a (dumb) wireless Access Point, after following the guidelines on your main page (DHCP disabled, firewall disabled, etc)
he is connected to a main router, via 1 Gbps wired cable, gateway 192.168.1.1, with 192.168.1.10 address
-Mode: Master | SSID: BlaBlaBla-Ble123
-BSSID: XX:XX:XX:XX:XX:XX
-Encryption: WPA2 PSK (CCMP)
-Channel: 9 (2.452 GHz)
-Tx-Power: 18 dBm
-Signal: -43 dBm | Noise: -95 dBm
-Bitrate: 72.2 Mbit/s | Country: PT
-Operating frequency: Mode N - channel AUTO - Width: 40 MHz
-Transmit Power: AUTO
-WMM Mode: on
-enable key reinstallation (KRACK) countermeasures: on
ALL WORKS GREAT, except the speed, i can only get 50 Mbps UP or DOWN.... as far as i'm aware, i'm supposed to get at least 100Mbps, right?
(to be honest, i don't know how they advertise 150Mbps via N wifi, if the WAN/LAN ports are all 100Mbps, but that's another story (me ignorant on the matter too))
Simple answer, old and lowest-end 802.11n hardware and a combination of 1x1 vs 2x2 stream combinations between AP and client. For good performance, you will need better hardware.
Disclaimer: this is a slight oversimplification, but still very close to the truth.
802.11n isn't thaaat much of an improvement over 802.11g, what it did change is:
using twice the channel bandwidth, from 20 MHz to 40 MHz
but, in practice, you don't get to use 40 MHz on the 2.4 GHz band due to interference and congestion, so your maximum link rate is already cut in half from the start
using two antennas -two streams- concurrently (MIMO)
for this to work, both AP and STA (the client) both need to support this, if your client only has a single antenna, you're down to one stream (1x1) and your remaining maximum link rate is cut in half again
802.11n devices, especially early ones, weren't really good at this game, so in practice the gains are lower than expected (down to non-existent for many USB devices, which technically do have two antennas, but too close to each other to be operated independently and provide a real gain)
slightly improved signal encoding methods
being the first generation to push 5 GHz (where 40 MHz channels actually work, compared to the 2.4 GHz band where they don't - unless you live in the sticks)
doesn't help you with this device, as it is 2.4 GHz only
The theoretical maximum for 2x2 802.11n would be 300 MHz, looking at the tl-wr740n v4:
only one antenna, so 1x1 (technically 1x2:1), which leaves you with 150 MBit/s theoretical maximum
as you already raised, the wired switch of this budget device limits this to 100 MBit/s max from the get-go.
as mentioned before, 40 MHz channel bandwidth is rarely possible in practice (72 MHz in total is free to use for wifi in the 2.4 GHz band, shared by all of your neighbours), so your maximum link rate is cut in half again (~75 MBit/s) - not than much more than 802.11g (54 MBit/s, which didn't support multiple streams (MIMO) or 40 MHz to begin with, so you really got your 54 MBit/s data link rate)
in practice, budgeting in the inherent overhead, you won't get more than half of the theoretical data link rate for your high-level throughput (read, your download rate), so you're down to maybe ~35 MBit/s effective throughput (compared to maybe ~25 MBit/s for 802.11g)
early or cheap (low-end) 802.11n designs (such as this tl-wr740, or the WiSoCs/ MCUs still used in smarthome appliances) were bad and stayed far below specified performance figures in practice.
In comparison, 2x2 (the maximum for most clients) 802.11ac will give you ~350-450 MBit/s effective throughput and 2x2 802.11ax around 650-750 MBit/s up to well over 1 GBit/s (and even more with wifi6e/ 6 GHz).
the speed won't be an issue at all, since the AP is really only for smartphones, and 50Mbps is more than enough for the job, but the issue kept bugging my brain
