Digital television is an all-or-nothing system. When the signal reaching your TV's tuner is strong and clean enough, you get a perfect picture. When it dips below the threshold the tuner needs, the picture breaks into coloured blocks, freezes for a second, or the sound stutters and drops out. That is pixelation, and it is almost always a signal problem rather than a fault with the television itself.
The good news is that the causes are a short, well-understood list, and most can be found with a methodical approach. This guide explains what is happening inside your system, the usual culprits in North and North West London homes, the quick checks you can make yourself, and when it is time to have an engineer measure the signal properly.
What pixelation actually tells you
Freeview signals are broadcast as digital data. Your tuner has to rebuild that data stream perfectly, and it uses error correction to patch small gaps. When there are too many errors for it to repair, the decoder has nothing sensible to show, so you see blocks, a frozen frame or a black screen with a 'no signal' message.
That is why the symptoms seem so abrupt compared with the old analogue fuzz. It also explains why a picture can look fine for days and then fail: the signal may be sitting just above the cliff edge, and a bit of rain, wind or a busy mobile mast pushes it over.
Water in the cable and failing connectors
Coaxial cable is only weatherproof while the outer sheath and the connectors stay sealed. Over the years, sunlight cracks the sheath, plugs loosen and moisture wicks into the braid. Wet cable loses signal steadily and badly, and the fault often shows up only after rain or on cold mornings.
Cheap or poorly crimped connectors are another frequent cause, particularly where the cable enters the house or joins a splitter. Replacing a damaged run with low-loss, double-screened coax and properly fitted connectors usually cures a problem that has been blamed on the TV for months.
Misaligned or ageing aerials
A rooftop aerial is a precision device exposed to every storm. High winds can twist it a few degrees off target, and that is enough to lose the weaker multiplexes while others still work, so you might find only certain channels break up. Corroded clamps, slipping lashings and tired poles make the problem worse.
Age matters too. Aerials installed for analogue broadcasts were not designed for today's mix of frequencies and HD channels. If the elements are corroded or the aerial is pre-digital, realigning it only buys time, and replacement is better value.
4G and 5G interference
Mobile networks use frequencies close to those used for TV. A strong mobile signal can overload an amplifier or an unfiltered aerial, and the result is intermittent breakup that has nothing to do with the weather. It often appears at busy times of day, or after a new mast goes live nearby.
A filter between the aerial and the amplifier or TV blocks the unwanted signals. Our separate guide covers how to spot the pattern and how the fix works in practice.
Amplifiers, splitters and multi-room wiring
Feeding several rooms from one aerial means the signal gets divided, and every split costs strength. A cheap splitter, an undersized amplifier or a power supply that is slowly failing can leave the furthest rooms with a marginal picture while the living room looks perfect.
Another common trap is a booster fitted where the signal was already strong. Over-amplifying can be as damaging as under-amplifying, because it overloads the tuner. The right answer depends on measurement, not on adding more gain.
Obstructions and changes around you
Reception that was fine for years can deteriorate when something changes in the signal path. New buildings, scaffolding with sheeting, a loft conversion, or trees growing into the line towards the transmitter can all weaken the signal reaching your aerial.
In North London, hills and dense terraces already create patchy reception, so even modest changes can matter. If the problem began after building work next door or after leaves came out in spring, this is worth mentioning to your engineer.
Quick checks and when to call an engineer
Start by finding out whether every TV is affected or only one. One TV points to the lead, wall plate or the set itself. Every TV points to the aerial, main cable or amplifier. Note whether it is worse in rain, wind or at certain times, and try a full retune using the TV's menu.
If every set is affected, or the fault returns, a meter-led test at the aerial and each socket will pinpoint the cause quickly, so you pay for the right fix rather than a replacement system you may not need. Call us on 0800 206 2385 or use the contact page.