Portable TV sets usually come with an integrated loop aerial fixed to the top of the device or a separate set-top aerial that you can place on or near the TV set. Unless you live close to your local digital-television Freeview UK transmitter, you might struggle to pull in a strong enough signal with a small portable TV aerial and may need to upgrade to a larger loft-mounted or outdoor TV aerial to receive all available channels. If this isn't possible due to local planning restrictions or it's beyond your budget, you can try maximising reception on your existing portable TV aerial.
Consult an online Freeview UK TV reception guide (see Resources) to find your local TV transmitter. You need to know the approximate direction and distance of the transmitter from your home and whether the signal is vertically or horizontally polarised.
Push the TV aerial cable firmly into the aerial input socket on the back of the portable TV set. A loose cable connection can degrade the signal that the TV receives from the aerial and lead to loss of some or all Freeview channels.
Turn on the TV set and switch it to a channel with weak reception. A weak signal typically causes video pixelation, audio problems or complete loss of the TV signal. Adjusting the portable set's aerial on a channel with poor reception should maximise the signal strength across all available channels.
Twist and angle the loop aerial slowly while watching the TV screen. Leave the aerial in the position that achieves the most stable video and audio signal on the displayed channel. If you have a standalone portable set-top aerial, move the position of the aerial to achieve the best signal. Also ensure it's correctly polarised with the aerial element bars arranged either vertically or horizontally, depending on the radiation pattern used by the local transmitter. In some cases, you may receive better reception by raising the aerial's height -- try placing it on a nearby shelf or another suitable surface rather than on top of the TV set.
Install a set-back TV signal booster. You can buy signal boosters, also known as TV aerial amplifiers, from online electrical retailers or high street electrical shops. Plug the aerial cable into the input socket on the booster, plug the booster's output cable into the TV set's aerial socket and then power on the device. A signal booster can sometimes raise the signal by enough to significantly improve TV reception.
Also experiment by placing the portable TV set in different rooms and different positions in your house or flat. You're much more likely to get a satisfactory signal near a window in a room that faces the direction of the TV transmitter rather than a back room where the signal has to travel through several walls to get to the TV aerial.
Some portable TV sets come with a "rabbit's ears" aerial in addition to the loop element. If so, ignore this as it is intended for VHF reception, which is not used for TV broadcasts in the UK.