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Have you tried reversing the polarity on the ballast?
On your range extender are you using 2.4G or 5G EXCLUSIVELY?
Also, is there a firewall or other software reducing your throughput?
bkmk
As a test get a long cat 6 crosdover cable and connect the computers back to back to eliminate network bottlenecks and isolate the issue
Do you have access to the cable modem that would allow to make changes if necessary ??
The reason I ask is, the Ethernet port may only be capable of 100mb and if it can do 1gb it might be hard coded to 100mb and what happens is your cable modem and pc will auto negotiate to a compatible speed in this case 100mb
The only solution if the cable modem can only do 100mb is to upgrade to one that is capable of 1gb otherwise you are spinning your wheels
powerline adapters rather than range extender
Is there anything else connected to your extender ? If so, it defaults to the speed of the lowest device.
First thing I would do is work to isolate the problem. Turn off your WiFi on the PC, then plug your PC directly into the TP-Link router and check your speeds there. If as fast as you expect, then disconnect from the router, renable WiFi on your PC, and check your speed directly to the router. Again, if OK, then is sounds like the range extender might be maxed out. If slow, like originally via the extender, then the TP-Link WiFi router or settings are off.
I had a slow link through a TP-Link router. Problem turned out to be I had used an old CAT5 cable to link the internet modem to the router, and it couldn’t handle the higher speeds that both the modem & router were capable of. I separately had a problem with a router setting, where I had bandwidth controls set, and they weren’t high enough to support the higher data-rates the other gear was capable of - effectively throttling speed down.
10BASE-T: UTP category 3, 4, 5 cable (maximum 100m) EIA/TIA-568 100Ω STP (maximum 100m)
100BASE-TX: UTP category 5, 5e cable (maximum 100m) EIA/TIA-568 100Ω STP (maximum 100m)
1000Base-T: UTP category 5, 5e cable (maximum 100m)
The TP RE 350 has a 10/100 RJ-45 output.
So you are using WiFi to the range extender and hard wire to the computer? Then the bottle neck is the range extender. Look at WiFi 6 for greater range and speed. This should give you the range and speed thus replacing the range extender. Check you WiFi card speed capability 1st, may need up grading.
https://www.tp-link.com/us/wifi6/best-wifi6-router/
Are you sure the link is reporting 100MB, or is it 100Mb? THe case of that "b" is important.
100MB is roughly 800Mb, which is close to your expected 1Gb connection.
Most providers advertise in Mbps, rather than MBps because the numbers are higher. From your explanation, I think you are OK, though I would confirm the 100/100 up/down speeds (B vs. b).
Bkmk
I had a similar problem, and it turned out I was being throttled by my ISP. It was inadvertent on their part, but I had to prove it to them before they would fix it. It took two hours on the phone with a competent tech after I was blown off by other phone techs.
I showed them the problem by using a hard wired CAT5 connection directly out of their modem to my PC, with no router and no switches in the picture still had slow speed.
I heard range extenders cut the effective bandwidth at least in half, because they have to both receive and send the signal. Wonder if there is a bottleneck there.
Did you try rebooting? Unplug, wait one minute and- sorry, I couldn’t resist.
I also run cat7 cables for all the direct connection. (Upstairs all laptops run on either 5g WiFi or hardwired) and getting way more than you are.
Cat6 cabling might be an issue or it might be also the max limits on that RJ45 port too.
Is there a switch or a hub between your computer and the modem/router? Slow networking hardware can become a bottleneck.
When you get upgraded, have the tech also replace the connection from the wall to the modem with Cat7 or Cat8 so that's not a bottleneck.
Lastly, those TPLink extenders don't work as mesh so you can't daisy chain them for extended coverage. You need a wifi system that is built as a mesh met. (We upgraded to one that can handle the digital loads and it's worlds of difference.) But if you prefer the extender, make sure that the 2.4ghz is turned off and only running on 5G for anything that connects via wifi.
Your connection can be 100 megabit or 1,000 megabit. It can’t be 500 megabit. Units of measure matter - 100 Mb is 100 million bits per second (roughly) and 1 Gb (or gig) is roughly 1000 million bits per second. Upload and download speeds may be in bytes. There are 8 bits in a byte so 12 megabytes down is about 96 megabits down - that would be really good on a 100 megabit connection. One convention is lower-case b means bits, uppercase B means bytes. There is a path from your house to the server. If the entire path is gig, then you could potentially get gig throughput. If there is any leg that is less than gig, say 100 megabit, then your connection to your wireless network appliance might be gig but the throughput would be limited to 100 Mb.