TV and Radio signals can be affected by atmospheric conditions, including high air pressure which brings fine weather.

On Freeview, this may result in temporary picture break up (pixelation) or you might receive signals from outside of your area.

On Radio, this may result in a weak signal or complete loss of service. 

Broadcasters can’t prevent it, and adjusting your aerial will make no difference, and reception will only improve when the weather changes. 

High Pressure (Atmospherics) 

Weather related interference occurs mostly in the summer months when periods of high pressure can cause radio waves from distant transmitters to travel further than normal which can result in interference. 

The diagram below shows the sun heating the ground and the warm air getting trapped between the colder air. When this happens it creates a layer that mirrors the television signal. 

 high pressure weather

It is not possible to exclude completely interference due to the weather, but broadcasters do their planning on the basis that viewers and listeners should be free from this sort of interference for at least 99% of the time, providing they live within the service area of their transmitter and are using a good directional aerial.

Since we cannot control the weather, we have no influence over abnormal propagation through the troposphere and it is only practicable to plan a network where interference is suffered no more than 1% of the time. To improve on this figure, broadcasters would need to increase the number of transmitters drastically and build a much denser network. This is impractical and would be very expensive.  Unfortunately, tropospheric-type interference is never spread thinly throughout the year. It tends to happen mostly in the evenings - when television viewing is at a peak and specialist FM programmes are on air. (FM listening peaks in the morning). It often appears at the same time on consecutive days, then disappears for several months. Some years are worse than others, depending on the prevailing weather patterns. Nevertheless, when averaged over several years, the majority of viewers and FM listeners should not be troubled by weather-related interference.

Network Planning

In the United Kingdom alone, there are over 1000 television transmitters sharing the UHF TV frequencies. In Western Europe, where the same channels are used, the number of television transmitters most likely exceeds 30,000. Similar congestion occurs within Europe on FM radio frequencies. Neighbouring countries must coordinate their network planning so that mutual interference, even during periods of abnormal propagation, is kept to an absolute minimum. It is impossible to plan a network which is totally free of interference but broadcasters can protect their transmitter service areas for the majority of the time. This can be achieved by carefully choosing the channel groups and aerial polarisation used at each station. Additional protection can be obtained by using directional transmission characteristics, where necessary, and by using natural features such as (hills, mountains) to maximum advantage. In the case of UHF television, transmission frequencies can be "offset" slightly to minimise the subjective effects of possible interference. Last but not least network planning assumes that the viewer/listener will fit a good directional aerial to keep out unwanted signals arriving from directions other than the wanted signal.

Nocturnal Inversion

This type of inversion can occur after dark if the land cools more rapidly than the air above it. During the daytime, the sun heats both the ground and the air and there is a normal fall of temperature and refractive index with height. In the evening, the ground cools rapidly and the layer of air closest to it becomes colder than the layer immediately above. Around dawn, the air in contact with the ground is at its coolest and may also be very moist, resulting in fog or dew. As in the case of the advection inversion, the sharp contrast between the two layers of air - one cool and foggy, the other warmer and drier - provides the right conditions for long range propagation of VHF/UHF signals. Nocturnal inversions occur exclusively over the land as the ground can cool much quicker after sunset, than the sea.

Advice for TV Viewers:

If you have tried auto tuning your TV receiver, this may have caused problems as it may have picked up channels from an incorrect transmitter. We recommend you carry out a ‘manual retune’ which allows you to select the channels you require from the correct transmitter to which your aerial is pointing. To find out which transmitters cover your area please use our Interactive Transmitter Checker. Information on how to retune manually is within the Interactive Transmitter Checker. You need to Select your transmitter from the left hand side, then select Quick Tips and Download Manual Retune Instructions

For more information on why you need to perform a Manual re-tune please visit our Manual re-tune page.