@bobdeco1 

Let's start with basic understanding of what you have, which may lead to recommendations. 

Can you confirm that Disk C is connected to Disk B and not to Main Deco (which is Disk A in your description). Also, please share screenshots of Signal Source reported by both your Satellite Decos (Disk B and Disk C). You can find it in Deco app in Satellite Deco information screen, and this is an example from my Deco M9 Plus:

You should see at least two blue bars, or better - three. Less than that - it is a problem.

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What is firmware version of your Deco nodes? You can find it under Update Deco, in Deco app.

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Can you describe how all three Deco positioned in relation to each other. Is it straight line: A <-> B<-> C, or different layout?

If it is straight line, what is the approximate distance between Disk B and Disk A.

  @Alexandre. 

Thanks for your response

Based on the app, I can confirm that Disc C (Study) is connected to Disc B (hallway) and Disc B is connected to Disc A (bedroom) which is the main Deco.

For hallway (Deco B) it says

Signal source Bedroom, 2 bars, 2.4 GHz/5GHz_1/5 GHz_2

For study (Deco C) it says

Signal source Hallway, 2 bars, 2.4 GHz/5GHz_1/5 GHz_2

Firmware it says it's currently up to date

1.5.6 Build 20211018 Rel. 356.17

The layout is that A is in a bedroom, B is below it in a hallway about 5/6 meters away, C is in an adjacent room about 4/5 meters away with the flow as A <-> B<-> C. 

  @bobdeco1 

You have latest official firmware. What you describe is standard with dual-band WiFi mesh, where each hop cuts speed by half. You trade speed for signal strength and better coverage. With dual-band WiFi mesh, Disk C will have half of Disk B speed.

I would have expected tri-band Deco M9 Plus do better. I would have expected Deco C lose some speed, too, but not exactly half. 

There is another thing I am curious about: you may have seen on that forum that Satellite Deco often prefers connection to Main Deco, and that is for the reason of less hops. In your case, Deco C connects to Deco B instead of Main Deco, and you verified that.

Can you do another test for me: power off Deco B. See if Deco C can connect to Main Deco, if it can - what its Signal Source and what will be the speed (wired preferably, or wireless) on device connected to Deco C in that setup.

  @Alexandre. 

Thanks

I did as you said and turned off B. C can connect to A, however the signal is

Signal source Bedroom, 1 bar, GHz_1/5 GHz_2

so barely functioning and the download speed is roughly 4Mbps 

  @Alexandre. 

Just did some playing around of the height position of the disc C and if I place it higher in the room, I can get 200mbps it. Obviously still some reduction but it seems that there is some interference which height seems to help with!

Not sure there is much else I can do?

  @bobdeco1 

Weak signal between Disk C and Disk A makes sense. Disk C should have connected to Main Deco if signal was reasonably good. Thanks for verifying it.

There are no settings in Deco mesh to change to boost the signal. It is consumer grade WiFi mesh.

I can give you two options, and sorry if they are obvious. One is to connect Disk C with Disk B by Ethernet cable.

Another is to move Disk B and Disk C closer to each other. I know, you don't believe this can change anything, but I suspect that maybe third backhaul band, which is 5GHz, is too weak and by moving two disks closer to each other it might actually start working, increasing speed substantially. You can either move Disk C closer to Disk B, or move both closer to each other, but if you move Disk B make sure its Signal Source to Disk A does not drop below two bars.

Also, if there is a wall between Disk B and Disk C, you can wall mount Deco M9 Plus on the wall, using third party wall mount holder. If you are interested in that option, I can give you brand name and other details.

bobdeco1 wrote

  @Alexandre. 

 

Just did some playing around of the height position of the disc C and if I place it higher in the room, I can get 200mbps it. Obviously still some reduction but it seems that there is some interference which height seems to help with!

 

Not sure there is much else I can do?

  @bobdeco1 

Just saw you reply, so I'll add to mine: you can even ceiling mount Deco M9 Plus.

  @Alexandre. 

Thanks for your time and efforts today