Slow powerline speed with OpenWrt on Archer A7

Hey, there! Recently I bought a new router and installed OpenWrt on it. Now my internet download speed via powerline is much slower (upload still fine).

Promised internet speed: 100 Mbit/s down, 10 Mbit/s up
speedtest.net result on old router via powerline: >90 Mbit/s down, >10 Mbit/s up
speedtest.net result on new router via powerline: <40 Mbit/s down, >10 Mbit/s up

(For comparison: The computer directly connected to the new router via LAN even gets 105 MBit/s and my phone gets ca. 80 MBit/s via 5 GHz too.)

Old router: Netgear WNR2200 with stock firmware
New router: TP-Link Archer A7 with OpenWrt 21.02.1

I'm using the same Windows 10 computer for the speed measurement.
The computer is connected to the new router via the same powerline adapters as before.

In the meantime I connected my TV via an additional powerline adapter (same brand and product as the others) but during the measurement the TV was turned off.
Before my switch to OpenWrt, the TV was connected to the internet via WiFi.

I did not try out the powerline speed on the new router with its stock firmware because I want to keep using OpenWrt.

What might be the problem? What should I do?

Thank you!

You have not mentioned make & model of powerline adapters.

Are the powerline adapters plugged directly into wall socket?

Powerline systems are susceptible to electrical noise. Perhaps the A7's power adapter is electrically noisier ?

Can you move the powerline adapter to another wall socket on other side of the room?

Install your WNR2200 between the Archer A7 and the powerline adapter. You may need to change the LAN IP address of the WNR2200. eg. use 192.168.111.1. Set the WAN to use 'DHCP'.

Assuming the Windows 10 computers is wired by ethernet to another powerline adapter located in another room, run a speed test to see if there is any improvement.

All powerline adapters are from TP-Link. On their label it says "TL-PA4010 (AV600)". They're plugged directly into the wall socket.

I'm currently wainting for an Ethernet-USB adapter to be delivered so that I can measure the internet speed with my laptop via different wall sockets and setups. (The other computer is a desktop PC that I can't move around.)

@bill888 I was unable to get the WNR2200 to work between the Archer A7 and the powerline adapter.

I performed multiple measurements with different powerline adapters, different cables and two different laptops and various different wall sockets in different rooms. However, I never got more than 40 Mbit/s :confused:

Strange WNR2200 did not work.

Ignore the power line adapters

Does laptop work in configuration below to verify WNR2200 is daisy chained to A7 router's LAN port ?

Internet === Archer A7 === WNR2200 === laptop ethernet

Make sure WNR2200 is set up to use DHCP for wan connection, and remember to change its LAN IP address (eg. 192.168.3.1)

Something else you can try?

reinstate the WNR2200 as your main router. Check power line speeds.

Turn on the Archer A7 (not connected to internet or anything else). See if power line speed through WNR2200 falls due to electrical interference from A7 or A7 power adapter when you turn the powerline adapters off and on.

Ensure WNR2200 and A7 use same AC mains power outlet.