You'll be pleased to know that it's pretty straightforward
First things first... All you need is some good quality aerial cable, a few aerial plugs, and a Sky magic eye. A spare Sky remote control also comes in handy. The other thing to check before you spend any money is that the bedroom TV has an analogue tuner. The analogue tuner thing is important, because this is what we shall be using to see the picture from the Sky box downstairs.
Let's presume you have a TV capable of picking up Freeview; that's the digital tuner at work. The analogue tuner is what we used to use before Freeview came along. It's what we used when there was only 4 or 5 TV channels from the aerial. This is important to check because lots of new smaller TVs are coming without an analogue tuner. If you have the remote control and user manual handy then have a look at what the manual says about changing inputs. You can also find on some remotes that there's a button marked "TV/DTV". This swaps between the analogue tuner (TV) and digital tuner (DTV). If you are sure your upstairs TV has an analogue tuner then you're all set to go.
The parts you'll need are:
1x Sky eye There are a few different designs, but the type like the one in
this link works the best because the little aerial wire makes it easier to connect at the TV end (less stress on the socket, no need to have extra cable joints, lies flatter if the TV is wall mounted) and the little square eye receiver thing is really unobtrusive
1x RF- or aerial back-to-back connector
Some
good quality coax cable LINK to WF100 on Satcure site. This WF100 is good without going silly. It's far far better than the cable that comes packaged with those aerial extension kits that are sold in DIY stores and supermarkets. They use poor cable and the picture quality after all your hard work really won't be as good as it could be. Get WF100 and you'll have the best you can get without going silly. Satcure sell it in different colours. They do white as well as the more usual black and the brown.
2x RF male plugs
You'll probably need some cable clips too.
Once you have all the bits, then start at the upstairs TV end. Switch the telly off, and unplug the existing aerial wire. In its place, plug in the Sky eye fly lead end. Put the little square receiver end somewhere it will pick up the remote signals from where you will normally sit. There's a sticky pad on the back. I usually fit them to the bottom edge of the centre of the frame of the TV. Now fit your coax plug to the WF100 wire you bought. Plug that in to the socket side of the Sky eye.
Next, run the cable downstairs. Clip it to skirting etc as needed.
When you reach the Sky box, cut off any excess from the cable you are running, then fit the other aerial plug. Then add the back to back (barrel) adapter. Switch off and unplug your Sky box. This wire with the barrel connector goes to the Sky box socket marked RF2. Put everything straight and plug in the Sky box. It will take about 10 minute to reboot. Good time to grab a glass of something chilled
Make sure the Sky box is on. You now need to go in to the Sky box menus and switch on the 9 volt power that will make the Sky eye work. The exact method depend on the type of box you have, but most now have the black Sky HD box; so the key sequence is Services.....0.....0.....1.....Select. The instructions that come with the Sky Eye should list the options for other boxes.
The service menu will appear. It'll probably default to "Setup", so use the cursor keys on the Sky remote to choose the heading "RF Out". There should be a menu that gives "RF Outlet Power Supply" as on item. Navigate down to it and then use the left or right key to make the choice of ON. press the green button so the box remembers the setting. You can press Sky to quick exit from the menus.
Before you go back upstairs put your Sky box on either the TV Guide or on to channel 995. This will help you identify the Sky box signal.
Take another glass of something cold upstairs. Check that there's a little red light on the magic eye... If not, go back downstairs switch off and unplug the Sky box and recheck all your connections. There might be a single loose filament of the braid touching the copper centre pin somewhere, or you are connected to RF1 out rather than RF2. Fix whatever the problem is, switch back on, channel 995 or TV guide, back upstairs.
Put the TV on, switch to the analogue tuner. Go in to the setup/tuning menu. Select the analogue tuning option. Scan until you find the the Sky TV guide or channel 995. Follow the TV instructions to store the channel.
BTW, the TV Guide does go off after a while if left unattended. But as long as your Sky remote works via the link you can always put it back on again to help when tuning.
The above seems like a lot when it's written out step-by-step. But really all it is is an extension from the Sky box RF2 out, then adding an infra red receiver, and a bit of TV tuning. If you have an aerial connected to the Sky box downstairs then you'll still get Freeview on the upstairs TV. Also, it's worth pointing out that although you have full control of the Sky box (including play, rewind, pause, recording and playback) that the picture upstairs is only a window on what the downstairs TV is seeing when switched to Sky. IOW, you can't watch two different Sky channels at the same time. For that you are best off ordering Sky multiroom.