Analogue TV -
A generally faint or grainy television generally caused by a weak signal. Normally the TV transmitter will be a long way away. A possible improvement could be made by reducing the aerial downlead losses, installing a high gain aerial and by adding a low noise masthead amplifier or signal booster. In a small number of cases a snowy picture can also be caused by too strong a TV signal, customer services will provide assistance.
'Herringboning' is generally caused by a too strong TV signal or possibly by a local high power transmitter such as CB Radio, radio amateur or radio taxi. Your TV sound may be affected as well as the picture. Contact the Radio Authority for further information.
'Ghosting' is observed when certain reflected signals are Picked up by the aerial in addition to the wanted direct line of sight TV signal from the transmitter. 'Ghosting' will appear as
multiple pictures on your screen and is usually caused by reflections from a building or other tall object. If the 'ghost image moves to and fro, the problem is likely to be reflected signals
from nearby trees moving in the wind. 'Ghosting' can only be improved by adjusting the height and/or position of your aerial or by adding a aerial with a larger reflector. 'Ghosting' cannot be improved by adding a signal booster.
In some areas of the country and under certain weather conditions you may receive two programmes from different transmitters on the same channel. This may appear as strong horizontal lines on the screen. TV announcements are usually made when the effect is
persistent over a wide area. Contact the BBC Engineering Information Department, ITV or the Independent Television Commission.
Interference can occur on both picture and sound. An uneven band of spots or lines indicates that the problem comes from equipment like a vacuum cleaner, fan or electrical drill. Try switching the appliance off to see if the interference stops. If it does you have located the source. All modern household appliances are required by law to suppress interference, so contact the supplier of the equipment.
A burst of interference caused by the operation of a central heating system timeswitch or fridge/freezer switching on and off. This may also be heard on the sound. It may be necessary to replace the thermostat or switch as these sometimes deteriorate with age,
so contact an electrical supplier. If the interference seems to be coming from a neighbour's house, approach your neighbour politely. Remember that they may be completely unaware of the interference and that the problem could be that your set is not properly protected against interference. Contact the Radio Authority for more information.
Digital Terrestrial Television -
Unlike analogue TV signals that can still be viewed under weak signal strength conditions, with digital terrestrial signals blocking/freezing and/or loss of digital picture and sound can be caused by insufficient digital signal and carrier to noise ratio. Similarly blocking and even a completely blank screen with no sound can result if the input signal to the set top box is too high. The digital cliff refers to the rapid change from the picture and sound being perfect, to disappearing altogether. When interconnecting equipment and to get the best carrier to noise then place the digital terrestrial television set top box as the first item in the signal path followed by any video or satellite receiver.
Digital signals are generally immune to ghosting or multipath reflections. They remain perfectly receivable under conditions where an analogue signal would suffer ghosting. For specific help with DTT reception problems contact the BBC Freeview, and for further general information contact the DTG Group.
To improve weak digital terrestrial signals try the following: move the aerial outside, reduce the aerial downlead losses, install a high gain aerial, add a low gain, low noise masthead amplifier or signal booster close to the aerial.
Analogue Satellite Television -
'Sparklies' or horizontal black or white tails on screen, are generally caused by a weak or mis-tuned signal. Examples which may cause a weak signal include the dish moving
off-beam, problems in the coaxial downlead, water penetration and deterioration of the LNB. Under severe weather such as heavy rain or snow 'sparklies' may also be
experienced. Similar problems can be caused when the receiver is not properly tuned and locked into the satellite channels.
Under certain conditions co-channel interference results because two programmes that are on the same frequency but from different satellites are received simultaneously. This may
appear as a mixture of 'sparklies' and vertical horizontal bars on the screen from the unwanted satellite channel. This is usually caused by insufficient rejection of the unwanted satellite due to the satellite dish being misaligned or too small in size resulting in it having a larger than required reception angle.
Digital Satellite Television
With digital reception, a weak signal or incorrectly aligned dish will cause the picture and sound to block or disappear. Check both the alignment of the dish and skew angle of the LNB.
Make sure all RF cable to connector joints are tight (both inner and outer) including all flyleads and outlet plate connections.