Can't move 5ghz channel on BT Smarthub 5 & 6

[#1]

Hi.

I used to have a BT Smarthub5 and replaced this with a BT Smarthub6 (set up as per Baldrick's instructions OK).

However, this still did not give good coverage to the far side of the house, so I set up the old smarthub5 as an access point connected to Smarthub6 by a powerline connection. This has sort of worked, but I do have an issue. I moved the wi-fi channels of both routers so that they did not clash with each other or with the neighbours. This worked OK with the 2.4GHz frequency (now on channels 3 & 11) but with the 5GHz channels I can't shift them from using channel 42. BT smart hub manager tells me they have moved to channels 48 and 36; however the WiFi Analyzer app on my phone shows them as CH 48(42) and CH36(42) and it is channel 42 that they are both using! Despite me telling them to move they seem determined to keep using the same channel and I can't shift them!!

Anbody got any ideas what is going on?

[#2]

@RealityDysfunc  Welcome to the forum.

Have you tried closing WiFi analyser and restarting it? Alternatively try switching the Smarthub off for a few minutes so that it reboots.

[#3]

What bandwith are the 5GHz channels set to?
I am guessing 80 MHz and the Homehub only supports channels in the range of 36 to 48.
Reduced them to 40 MHz, then they will move to 38 and 46.
See the diagram at: https://www.silextechnology.com/unwired/changes-to-the-5ghz-wi-fi-band-in-the-uk

[#4]

Ah, the good old switch them on and off again trick! Pretty sure I have already tried this, but I will try again when wife has finished using internet for work.

[#5]

Yes, appears to be using 80MHz. How do I change this, and what are the implications of doing so?

[#6]

I do not use a Homehub so I cannot advise how to change the channel bandwith.

There is guidance re channel bandwidths here:

https://www.cbtnuggets.com/blog/certifications/cisco/when-to-use-20mhz-vs-40mhz-vs-80mhz

see the section titled: 5 Ghz Wi-Fi: 20 MHz vs 40 MHz vs 80 MHz

A 40 MHz wide WiFi signal maximum speed will exceed the maximum download speed on FTTC.