This page will look mainly at Freeview but most of the comments apply equally to satellite. Cable is the third option for getting digital signals into the house but is limited in its coverage of the country as a whole. Therefore I don't intend to include it in this page.

What's all this analogue and digital stuff anyway?
The old-style analogue transmissions are in the form of variable radio waves. Imagine you're standing at the side of a street watching an emergency vehicle approaching with its siren going. As it passes you the pitch of the siren drops. This is because on approach the waves are being compressed (so the frequency is higher) and as the vehicle travels away the waves are being stretched (so the frequency is lower). If the vehicle accelerates, the effect will be increased and the pitch will drop further. So in a television signal, by varying the frequency of the wave form, the signal can be made to convey patterns that inside a receiver are converted into a picture. That's analogue in a nutshell.

Digital transmissions on the other hand are sent as a rapid stream of zeros and ones. Again, a suitable receiver can process those into a picture. An approximate analogy is morse code where patterns of long and short pulses equate to alphabetic characters forming a message. Digital signals have been around for many years; CDs and DVDs all use digital technology for example. The big advantage for TV transmissions is that for any given bandwidth, far more digital channels can be carried than analogue and therefore it's far more efficient. It also offers the opportunity of much higher picture and sound quality, but the main advantage for the Government is that once the analogue signals have been switched off, it can sell off huge chunks of the existing bandwidth to buyers such as mobile phone companies who have an insatiable appetite for it and are prepared to pay handsomely to get it.

Background.
Over a period of 4 years from late 2008 to 2012, the traditional analogue TV signals will be switched off. They're being switched off region by region, starting with Border in the second half of 2008 (the full schedule is shown at the bottom of this page). When that happens, virtually all older TVs and video recorders will cease to work by themselves, and each one will need to be replaced or equipped with a separate digital set top box (STB). Your television remote control will be more or less redundant except for turning it on and off and adjusting the volume, and all channel settings will be done using the STB. Those people already equipped with satellite or Freeview will be familiar with that and better placed to cope.

What will it mean for householders?
Those people with Sky Plus already have a head start. They will probably be far more likely than the rest of the population to use digital signals exclusively, and they won't be bothered about setting timed recordings in the traditional way. Everyone else will have to change the way in which they watch, and especially record, TV programmes. Currently, a single aerial will feed any number of separate receivers (subject to signal strength), so video recorders and TVs can be daisy-chained together using the RF loop-through sockets.

All that will change. Each standard STB, whether it be a Sky digibox or a Freeview receiver, can only pick up one frequency at a time. This means a separate receiver will be needed for each and every TV and video in the house. Not only that but each one will require its own connection to a power point. You also need to be careful about buying more than 1 of a specific make if they're to be used in the same room. The remote controls, especially with cheaper models, might affect both STBs with irritating results.

In some parts of the country, Freeview receivers will work quite happily with existing aerials but not everywhere (we are amongst the lucky ones and we have a Freeview recorder as well as satellite). Digital terrestrial TV signals (DTT) are currently transmitted at relatively low power and that won't change until the analogue signals are switched off. Therefore in all but the strongest signal areas, it might be necessary to upgrade your aerial, adding further expense.

And the changes don't stop there. All digital receivers are designed to receive over-the-air software changes, and that applies as much to Freeview as to Sky. Therefore, all digital receivers need to be left permanently connected to a power supply so that they can receive any updates as and when they're transmitted. So you'll not only have more equipment, your electricity costs will increase as well! It could also create a problem for anyone who habitually knocks off the electricity supply when they go away for a period of time, because they could return to find their digital receiver no longer works properly.

All new TVs available for sale are now capable of receiving Freeview, but unfortunately they still have to have analogue tuners as well, which makes them expensive. Eventually, twin analogue/digital sets will disappear altogether, as happened with twin 405/625 line sets in the late 60s, and prices will then drop further. DVD and hard drive recorders are also now available with Freeview built in, and as with Sky Plus there are some with twin digital tuners capable of recording more than 1 channel at a time.

The good news is that DTT will give you many more free channels than the 5 available on analogue. Whether you will choose to watch any of them is a moot point but then lots of people said the same thing when the original 2 channels became 3 with the launch of BBC2 in the early 60s!

What will it mean for caravanners?
All of the above points apply equally at home or away but there are some additional issues for caravanners. The first is that most modern caravans are fitted with omni-directional TV aerials such as the Status 315. These are easy to use as they require no aiming - they pick up signals from any direction. However because DTT signals are far weaker than analogue ones, at least at present, a basic Status aerial will have difficulty pulling in any kind of usable signal. Moreover, weak analogue signals provide a picture which though 'snowy' might still be watchable; digital signals don't: the picture is either perfect or non-existent. The Status 530 steerable aerial will give better results but will still not be as good as an aerial mounted on the roof of a house.

After switchover, the digital signals will be boosted and reception problems should then be at an end (though note that not everybody will necessarily be able to receive all the Freeview channels - this is called Freeview Lite and is discussed further down the page). Nevertheless, caravanners who visit different parts of the country will still need to use analogue equipment or an aerial capable of dealing with weaker digital signals.

The second issue is that of booster circuits on some caravan sites in weak signal areas. Many of the sites operated by the Caravan Club and the Camping & Caravanning Club for example are fitted with piped TV signals terminating at the hook-up bollards. They are almost exclusively analogue and will need to be upgraded as the region in which the site is located goes over to DTT. My understanding is that the clubs will upgrade their systems on a site-by-site basis as each region is changed over, and you should visit their respective websites for further information.

Finally, people who currently just have an old TV in the caravan will in future have to remember to take a STB as well (which will of course need its own separate power socket adjacent to the TV). If you also take a video recorder with you, that will also need its own separate STB! Caravan manufacturers will be delighted - we'll all need bigger caravans .

VideoPlus & Programme Delivery Control (PDC)
Most users of video recorders will be familiar with VideoPlus. Some might not be aware of Programme Delivery Control It's an electronic signal transmitted during programmes to precisely control the timer setting on a video or DVD recorder. Recorders equipped with PDC will record an entire programme even if it starts early or over-runs its scheduled time. Digital signals have a similar technology which digital recorders can use, but owners of basic digital receivers will have a more complex task to set and coordinate timed recordings. Not only will they have to make their own allowance for early starts or over-runs, but they will have to set 2 machines (the STB and the video or DVD recorder) instead of just the one.

Some makes of DVD recorder are now using technology called Guide Plus (http://www.europe.guideplus.com/) which works in a similar fashion to hard drive digital recorders, providing the facility to set a recording simply by highlighting the programme in a programme guide.

High definition transmissions
Many people are now latching on to the idea of high definition TV, encouraged by LCD and plasma models marked in the shops as 'HD Ready'. So let's examine what it means. First, it runs alongside the current digital transmissions - it doesn't replace them. So existing digital equipment will not be rendered obsolete (although that's not entirely true in the case of Freeview - see below) and it's up to each household whether to invest in HD or not. Secondly, HD-ready TVs won't pick up HD transmissions by themselves; they're simply able to handle the higher resolution. One exception is the range of Freesat-integrated TVs manufactured by Panasonic but otherwise, they will need to be matched with an HD set top box. At present, HD is only available via satellite and cable. Freeview does not yet have the capacity to carry HD signals but this will change in some areas, commencing with the Granada region in December 2009. However, note that current HD televisions won't cope so there'll be still more wailing and a gnashing of teeth! Both Sky and Freesat now have HD receivers but there is a £10 per month charge for using a Sky HD box.

Obvious conclusions
I think it's pretty obvious now that buying any analogue TV or recorder (probably second hand because all new products are digital anyway) would be a waste of money. If at all possible, look at buying digital equipment. Furthermore, video recorders are obsolete technology and you should consider a DVD recorder or preferably a DTR (digital TV recorder) instead of a video recorder. Indeed unless you want to save recordings for posterity, an DTR is definitely the type to go for. At present they are more expensive but the price is already dropping and will continue to do so.

Most models will allow you to record 2 channels simultaneously, whilst watching a previously recorded programme. A Sky+ recorder will normally cost £10 a month to activate the recording functions but that is waived if you take out any level of Sky subscription. Freeview and Freesat recorders don't involve any kind of subscription - you simply buy the machine, connect it to the TV and aerial or dish as appropriate and away you go. Provided your terrestrial signal is good enough to support a Freeview recorder, this is undoubtedly the cheapest way to go - there is now a wide variety of makes and models at prices well under £100.

Freesat recorders are more expensive because they're HD as well. They can typically record 80 hours of HD programmes or 200 hours of SD. They're made by Humax, a company that's been at the forefront of digital television technology for many years, and by Metronics. Because they use satellite transmissions, they're largely immune from the reception problems that can plague Freeview. All the digital platforms, Sky, Freesat, Freeview and cable (Virgin Media) have now adopted the same designation for their DTRs: a plus sign after the name. Thus we have Sky+, Freesat+, Freeview+ and V+ boxes.

However, whichever technology you choose, there are a couple of words of warning. The first is that DTRs, because they have an internal hard drive and a cooling fan, can generate noise and some makes are worse than others. At home it isn't normally noticeable, especially from a normal sitting distance, but in the confines of a caravan, the noise could well be more intrusive.

The second warning is one which you ignore at your peril! A year or so back, a friend of ours transferred some video recordings to DVDs. They were priceless family recordings, including footage of her late husband and shots of her daughter's 21st and graduation. Having checked that the DVDs had recorded OK she then wiped the tapes. Unfortunately her DVD recorder subsequently broke down and she replaced it with another make, at which stage she discovered the new machine wouldn't play those DVDs! The problem is caused by a little-known 'feature' of recordable DVDs - that in order to play them on other machines, they have to go through a process called finalisation which can only be done on the original recorder or an identical model. I was eventually able to recover our friend's recordings for her but it was a long struggle.

So if you have any important recordings that must be kept at all costs, make sure you've done it right before ditching the originals and that applies equally to any recording held within a DTR. Whichever recording medium you choose, you can't rely on it remaining usable in the long term. You only have to look back at the Betamax/VHS wars of the 80s, or more recently BluRay/HDVD to realise that your precious recordings may reach the stage where you no longer have equipment that will play them. The answer is to make sure you regularly re-record on to current devices.

Freeview Lite
I said above that the digital signals from the terrestrial transmitters will be boosted after the analogue switchoff but that's not the whole story. Even after switchoff, not everyone will be able to receive the full set of Freeview channels. The reason is technical and I don't understand it myself. However it's to do with the way that frequencies are arranged so that they don't cause interference (between adjacent transmitters presumably). The end result is that not all transmitters will carry the full complement of Freeview channels (though they will all carry the 5 main channels), and this is what's known as Freeview Lite. If you're affected and any of the missing channels are important to you, you'll have to consider going for a satellite solution.

Switchover schedule