In reply to a post by MHC:

Can you easily get a cable from the router to outside the house?

If so, get a outdoor AP, mount it on the wall facing the summer house, connect up and off you go ...

I'd like to look at the feasibility of this. It might be an option. I could get a cable (just to be clear, are we talking an Ethernet lead, not a co-ax cable?) from the Fritzbox router in the upstairs study, out of the window and down to the wall facing the cabin.

But can you give me a bit more of a steer on an "outdoor AP". Make, model, shape, size, specification? Does it need its own power supply? Cost?

In reply to a post by burble:

If you are happy to plug in a USB antenna into the laptop, and use 2,4mhz, then there are plenty on the bay for about £30, look for "long range wifi",

I'm up for whatever might work. I'll look at this and see what's available. It might turn out to be an easy option.

Your modest home will have a single phase electricity supply, i.e. only one live conductor and only one neutral coming in to the consumer unit from outside. All the live conductors to the upstairs and the cabin sockets and any circuit breaker contacts that they pass through will be capable of carrying 20 amps at 240 volts with little resistance and they will all be bonded to the incoming live conductor and thus to each other. Similarly with the neutral conductors. Thus in principle powerline adaptors should talk to each other on different circuits.

But another aspect is high-frequency interference impinging on high-frequency data transmission and here we move from science to art. Data links subject to interference lose bits of data but they have ways for dealing with this, including retransmitting the missing data. When the interference reaches a high level the data transmission is degraded and at a certain point can fall over completely.

The point is not directly about different circuits, more that different circuits likely run around different places where there is opportunity for interference to get in and for the wanted signals to be impeded. More joints potentially introducing resistance, and loops and adjacent cables providing opportunities for inductive and capacitive coupling.

Typical sources of interference are electric motors (e.g. pumps in appliances) and power supply units for electronic devices.

So you can understand why you have not been given a definite answer as to whether they will work. If your mains wiring has been done well and your area is electrically quiet they may work. You have a right to return anything bought online within 14 days of receipt.

Yes, an Ethernet cable and you would select an AP that use PoE (Power over Ethernet). A small PSU known as an injector sits by the router, and the router connects to the injector which then combines power and data on the outgoing port which cnnects to the AP. That gives you a powered AP.

I would recommend looking at some of the Ubiquiti ones but they are not cheap and around £160 + Injector and you need the UI software to manage it. So possibly not for you .... There are possibly cheaper options that others may know of.

Slightly more than op was looking at spending (£67) but a wireless p2p link would work well as long as you have line of sight
https://www.broadbandbuyer.com/products/19215-tp-lin...
Tplink P2P

There are 2nd hand Unifi Aps on ebay from £20. It may not be widely known but Unifi does support wireless uplink e.g. mesh mode.

Not the easiest but if you want reliable consistent wifi then they are hard to beat.

You may still find that powerline works fine and could even be as fast as your Internet connection - if you can get them on sale or return (or from somewhere with a good returns policy) then you can try them and see. It potentially could be your simplest solution and has a reasonable chance of working ok.

If going for a wirelss link, I would go for Ubiquiti NS5ACLoco. I use them personally and they are rock solid with 300Mbps easily achievable and can be pushed even more.

Thanks for those latest half-dozen posts. I always knew there would be a range of possible solutions. Making a decision isn't easy.

@Thinker27 clearly understands mains wiring. I don't! All I can say is that our simple domestic house wiring is about 30 years old. It was checked and modified a year or two ago when we had a new kitchen installed, and the consumer unit/fusebox was replaced with an up-to-date unit. There was already an external circuit to the garage in which there is a further fusebox with RCDs. And now for the summerhouse/cabin we have another external circuit feeding the cabin lights and power sockets through a fusebox also with RCDs.

I have a suspicion that this configuration might mean there will be some 'noise' or interference if we tried to set up a powerline link between router in upstairs study and laptop in cabin in garden, as this would travel via upstairs ring-main, household consumer unit, external power-supply to cabin, fusebox in cabin, and then to power socket. But as others have said, there really is no choice but to try it and see. So I might look to Argos for a sale-or-return kit like the TP-LINK 300M Wi-Fi Extender Booster & 600MBPS Powerline Kit at £45, rather than buying via eBay.

Can I suggest you post a plan view sketch of your home (upstairs) and 'cabin' with location of your router indicated.

That may make it clearer so suitable options are suggested.

I like the suggestion of an internal upstairs Ethernet cable to a location overlooking the cabin.
Then provide a wireless AP there, but internally (ideally by a window)