@mickevh, many thanks for that very informative reply. I'm sorry for 'polluting' the forum with my very basic understanding of wi-fi.
Not at all. I think you'll find you'll always get a sympathetic hearing from the "regulars" in this forum, so don't be afraid to ask any question no matter how "dumb" you might think it is.
The Orbi is a tri-band wi-fi system. Probably why it is more expensive than my existing HH5 which I guess is duel-band. In fact it sounds very similar to my wireless Davis VP2 weather console which receives a wireless signal from the station in the garden. It's a robust signal with 98% + signal quality. I previously had a cheap 'n cheerful Oregon Scientific system and the wireless signal would often be lost. The Davis kit was expensive but is nearly 10 years old and still working well. Money well spent!
Going back to the Orbi perhaps its tri-band wi-fi uses the same robust signal so strength stays high for longer distances. My cheap 'n cheerful BT HH5 seems to lose it quite quickly.
Let's step back a moment: All Wi-fi is availed by something called an "Access Point" (or AP, or WAP for short.) There's an AP built into a SOHO router along with all the other "get you on the Internet" stuff, but fundamentally an AP is an AP is an AP no matter what box it's built into.
So called "dual band" devices (routers and/or AP's) is like having two AP's built into a single box. One AP serves the 2.4GHz waveband, one AP serves the 5GHz (incidentally, concurrently.)
So called "Tri band" routers/AP simply take this idea one step further ans build three AP's into a single box, this time with one AP serving the 2.4GHz waveband and
two AP's serving the 5Ghz (each tuned to a different radio frequency.) In the SOHO realm "mesh" systems the second 5GHz
AP is used for AP-to-AP conversation between the mesh nodes. Again this can happen concurrently with the AP-Client conversations which serves to mitigate the "only one thing at a time can transmit" air time competition.
"Tri band" is nothing to with improving the radio signal transmissions, it's generally to try and mitigate air-time competition between AP-AP conversations and Ap-Client conversations.
It is possible to turn off wi-fi on the HH5 and if I remove all Ethernet connections it reverts to modem status. I'll just need a cable to connect it to the Orbi for internet access. I can plug my gigabit switching box into a Orbi Ethernet port and that should give me the same single network as I have now for wired and wireless kit.
Not unless HH5 has a "Modem Mode" as discussed previously - if not, HH5 is still a router no matter how you cable it or whether you turn off it's Wi-Fi. In any case, if it's working well enough with your ISP (BT presumably) then there's no reason not to continue using the HH5 as a router and leave all the ethernet devices cables to it.
If you want the best out of Orbi, et al, you might turn off the Wi-Fi on the HH5 (because Orbi cannot "talk" to the HH5 to handle the roaming hand offs as well as it does between itself.) But again you don't have to. Ideally, you'd leave your HH5 to handle ISP and cable ethernet duties and "just" use Orbi as a mesh Wi-Fi system cabled downstream of your HH5. IN such as situation, Orbi doesn't need to do all the "get you on the Internet" stuff, so it would be worth looking to see if Orbi will let you turn that off and just run them as AP's.
Let's just pick apart this "mesh" idea and explore what it's about.
Ignoring mesh for the moment, in a large site we put up hundreds of AP's in a "cellular" coverage pattern of hotspots to both reduce the number of devices in each cell (thereby improving the air time contention) and to provide the geographical coverage. We then connect all the AP's together to a cabled network system. Essentially we get data off the radio waves and onto the wires as quickly as possible because the wires have much more capacity and reliability that Wi-Fi. I call the cabled infrastructure the "backhaul" llinks, though I'm not sure that's a widely used industry term.
For some far flung outpost, maybe we cannot get a cable out there. For example, one college I worked for, the gardeners were out in a shed in the middle of nowhere and running a cable out to them was impossible. In such a situation, we'd stick as AP in their shed, then use a Wi-Fi radio link for both the AP-Client link
and a link to the AP in he "main" building nearest to their shed. The AP-AP link was often called a "mesh" link by the technology vendors. Essentially, in that locale we use Wi-Fi for "backhaul" link as well as servicing clients.
But that has a consequence for performance ("speed") as the backhaul and client conversations are competing for the same air time. Imagine message hopping main building to shed AP to client in shed - there's two "hops" over the radio link that cannot happen at the same time, so the message transmission (overall) takes twice as long, which manifests as less "speed."
With Tri-band AP's I can dedicate one of my 5GHz radios in my AP's exclusively to bachaul duties on a separate radio channel which eliminates the competition for air time between backhaul and client conversations and improves the "speed" (though not the link rates.)
....
Increasingly, domestic users are discovering that "one AP in the middle of the house" can't cut it, and need to make a "cellular" coverage pattern of multiple AP's and vendors are bringing forth products to address this need with a lot of automation built in to you don't have to do the "difficult" stuff, like plan the radio channel layout. Often they improve the "roaming" hand off's between cells also.
None of this is particularly new technology, it's just new to the SOHO realm. "Mesh" seems to be the buzzword that has been picked up as the way to sell all this as some shiny new thing.
Fundamentally, if you need to improve Wi-Fi coverage, you need to deploy multiple AP's in a cellular coverage pattern. The "trick" is how one establishes what I've called the "backhaul" links. "Proper" cabled ethernet is by far the best way to achieve backhaul. If that's impossible, then HomePlugs is probably next best. Failing that, it's also possible to use Wi-Fi to create the backhaul links, including using these "mesh" and "tri band" systems.
However, with Wi-Fi backhauls (however they are achieved) positioning of the nodes is important as the AP's need to be "in range" of a good signal from each other as well as the client devices.
None of this does anything to the radio "signals" - they are just as they have always been. "Mesh" and "Tri-band" offerings are not some silver bullet that magically makes the radio transmissions "better." What it's doing is allowing you to deploy additional AP's closer to where the clients are, then set up the backhauls for you automatically using radio links (instead of ethernet and HomePlugs.) By definition, if you deploy a new AP nearer to any given client, then said client will see transmissions from the AP as "better signal" - because it's closer by. Any additional AP would have done the same (whether it's called "mesh" "whole home" "airport" or anything else the marketeers think up.)