How do aerials work

The latter is the driven element which actually "collects" the signal. All the other elements either act to "focus" the required RF the directors and the reflector or prevent unwanted RF reaching the dipole the reflector. Note that neither the directors nor the dipole have to be in electrical contact with the boom. Yagi aerials, particularly high gain types, are very directional and it was this property which the Germans used when they were attempting to detect Resistance radio operators in WW2.

Operatives would be monitoring for any transmissions and by utilising the directivity of the antennas they could plot which direction they were coming from.

If two or three teams were doing this simultaneously the plots could be drawn on a map and the transmitter was at intersection of the lines. Above is a 13 element see element count TV aerial and 3 element DAB aerial, illustrating the main components found on Yagi type aerials.

Mounting cradles strengthen the aerial and also reduce the twisting forces exerted on the pole and clamp. End mounting aerials can exert a very high torque on the aerial pole when the wind blows. On the other hand Log Periodic aerials should always be end mounted, though our tests on this were inconclusive to put it mildly. On a related point if any aerial is fitted with a cradle this should always be fitted perpendicular to the dipole so as not to interfere with the tuning of the directors.

Similarly the pole can also interfere with an aerial's tuning , particularly if it is vertically polarised. For any aerial the tuning of the elements is critical. This is a highly specialised job and it is fundamental to the performance of the antenna. The other is an antenna inside the case, usually fixed to the main circuit board, and it picks up AM amplitude modulation signals.

If you're not sure about the difference between FM and AM, refer to our radio article. Why do you need two antennas in a radio?

The signals on these different wave bands are carried by radio waves of different frequency and wavelength. Typical AM radio signals have a frequency of kHz kilohertz , while typical FM signals are about MHz megahertz —so they vibrate about a hundred times faster.

You need two antennas because a single antenna can't pick up such a hugely different range of wavelengths. It's the wavelength or frequency, if you prefer of the radio waves you're trying to detect that determines the length of the antenna you need to use. Broadly speaking, the length of the antenna has to be about half the wavelength of the radio waves you're trying to receive it's also possible to make antennas that are a quarter of the wavelength, though we won't go into that here. Blogs Contact.

Blogs Need Help? Search Site. How antennas work Suppose you're the boss of a radio station and you want to transmit your programs to the wider world. Depending on what kinds frequencies of waves we want to send, how far we want to send them, and when we want to do it, there are actually three different ways in which the waves can travel: Artwork: How a wave travels from a transmitter to a receiver: 1 By line of sight; 2 By ground wave; 3 Via the ionosphere.

As we've already seen, they can shoot by what's called "line of sight" , in a straight line—just like a beam of light. This is the distance from peak to peak or from trough to trough of the carrier wave.

Ideally, the aerial needs to be the same length as the wavelength for best possible reception. However, at many frequencies, the wavelength is extremely long, making it impractical to make aerials that are the full wavelength. FM radio for example, would need aerials of a little over three meters long. That would be difficult to mount on a car and would tend to hit things as the car drove down the highway.

The higher the radio frequency, the shorter the wavelength. Cell phones, which work at a frequency of about 1. There are several ways of compensating for the problem with not being able to make an aerial long enough. One is to use an aerial which is an even fraction of the wavelength. Half wavelength and quarter wavelength aerials are common.

All the coverage predictions used in our tools assume you have an external aerial at 10m. If you are in an area that has very good coverage, you can use loft or indoor aerials. However, some of the signal strength will always be lost when using indoor aerials. This is becoming more prevalent with new properties as many have foil-backed insulation in roofs and walls. This sort of insulation blocks television and radio signals.

Indoor portable aerials tend to come in two varieties, mini replicas of external aerials and wire loops. The looped aerial will perform the worst and is unlikely to give you good reception. Indoor aerial. Please see our help page to see how DAB multiplexes work , Therefore, you may not be receiving this service, as there is not a commercial DAB service in your local area. To check what coverage of DAB services are available in your locality, please see our Transmitter checker tool.

Firstly, poor reception might be down to poor coverage, so it is best to check you are in a DAB coverage area. Use our transmitter tool , which will tell you what national and local DAB services are available in your locality.

Secondly, If you are in a good coverage area, and are still receiving poor DAB reception please try our Problem Assistant for further advice. DAB reception is rarely disrupted by high-pressure weather conditions, but under some circumstances, signals from very distant transmitters can cause reception to break up, or be lost for periods of time.

If you suspect this - particularly if you are also getting interference on FM - wait until the weather changes. The 5 Live Sports Extra schedule is available online. For more information on finding and storing these services, see our Help guide on DAB secondary services. This is because the power used is lower, and is forced to work outside of its normal operating parameters, resulting in electrical impulse interference. For more information on interference, please see our RTIS site.

Coverage and location. If you live in a basement flat, or your building is steel-framed or reinforced concrete, coverage may be affected. Most DAB radios can be tuned easily at the touch of a button. Sometimes a full scan is required. Portable radios should be tuned in a location in your home where the best possible signal is received. Most DAB radios come with built in signal strength meters which can be helpful.

From time to time radios should be re-tuned in order to discover new stations. Telescopic aerials. Telescopic aerials on portable radios should be fully extended to receive a good signal.

Tilting and swivelling the aerial will help to get the best signal. Broken aerials may affect reception. An externally mounted aerial can be attached to many types of DAB portable radio and hi-fi systems. An indoor aerial may be good enough, but for the best reception use an outdoor one. Ideally, this should be on the roof or high up on the outside of the building, though it may also give good results in the loft.

Cables and Connectors. If you have an external aerial, a radio signal will always lose some of its strength as it passes along the cable and through the connectors. It is important to minimise the loss by using good quality cable and connectors. DAB uses different frequencies from FM radio. We advise you check that your antenna is able to receive DAB, in the majority of cases you will need a new antenna.

An exception is "helically wound" FM aerials. See our guide on DAB radio in cars. Qualified Installer. The BBC cannot recommend individual Installers. The CAI Confederation of Aerial Industries is a recognised trade body which will can put you in touch with one of their members in your area. By using our Transmitter Checker , you can check which DAB radio services are available at your location.

It will also show you any transmitter faults. Works and Warnings. Check whether there are any known works or warnings that might be causing the problem. DAB uses multiplexes to group services together. The BBC network stations, e. Nations and Local radio services are carried on a mix of commercial multiplexes. Try switching your radio on and off. If this does not work, a full re-scan might be needed. Check your radio manual for specific instructions on doing a full re-scan.

Portable Radios. Try moving the radio around to see if you can find a better position where you get good reception of all the stations you want to listen to. In most circumstances the supplied telescopic aerial should be perfectly adequate, and as a rule of thumb DAB aerials tend to work best when vertical and extended at least 35 cm.

If your radio reception is poor then you could consider an external aerial for best reception quality. Even in good areas an external aerial will guarantee optimum performance and will also ensure consistent listening quality. Many Digital radios have a signal strength display which enables you to position the Radio for the best reception usually a number of blocks as a guide of reception quality. Unfortunately, some radios are less sensitive than others and need careful positioning to work reliably.

If your radio displays signal strength, use this as a guide to ensure the best position. Our DAB installation guide provides further information. External aerials. It is important to check the cables and the aerial for damage and that they are operating correctly.

Make sure any cables between your radio equipment and aerial are connected securely. For further information see our DAB installation guide. Damaged Cables.

Water can get into external cables and can cause reception problems. To rule this out see our guide on water damage to cables. Car Radios. Radio reception can drop out when on the move due to changes in topography. See our car radio guide for more information. Radio signals can be affected by fine weather including high pressure. The only solution is to wait for the weather to change, you should not re-tune during this time. Our information on h ow clear skies and fine weather can affect your radio reception may be useful, please see our weather guide.

If all other stations are working ok and you have just lost one station. The problem could be due to a number of reasons, the station may have stopped broadcasting or have moved multiplexes rather than a radio fault. All of the stations in one multiplex should be behaving the same way. If you are still having problems, it is possible an unwanted signal is the cause.

For information on the symptoms of interference see our sister website RTIS. The BBC cannot recommend individual installers. The CAI Confederation of Aerial Industries is a recognised trade body which will be able to put you in touch with one of their members in your area. You may need to contact your car manufacturer to check.

The best place to put a DAB aerial is on the roof of the car and as far from the engine as possible, to avoid any interference. If your car radio is showing no signal or no service for a station you usually receive, this could be down to one of the following things:. DAB Transmitter Fault.

If you know your location, you can use our transmitter checker to see whether there is a problem. If not, then check the radio and the aerial to confirm they are working correctly. Poor DAB reception can also be caused by equipment used in the vehicle. For example, phone chargers or dash cams sometimes cause interference and affect your radio signal.

Try unplugging the items to see if one of them is causing any interference. Delete the presets and re-tune to the services in your area. When travelling in the car, your signal can be affected by natural features of the land, for example, hills, valleys, rivers, etc. The signal should return once you move away from these features. Where can I find them? When Radio 5 Live Sports Extra is on air, you should find it right next to 5 Live on the list of stations on your digital radio.

It can be found next to Radio 4 on the list of stations. When do they broadcast? Radio 5 Live Sports Extra has a dynamic schedule. To see what is available when, the BBC keeps a schedule on the sport website. How to find these services. It is best to re-tune your radio when they are broadcasting, so it will store the station in its memory. It is worth first checking to see whether the problem is with your own equipment, or the local transmitter.

If neighbours are having the same problem it may be that the aerial itself is at fault, or there may be an interfering signal. In either case, you will need to ask your landlord or management committee to solve the problem. Checking for problems. Check cables and leads within your property to ensure the problem is not a simple installation fault. Please see our Freeview Installation guide for further details.

This will help you to see if there are, or have been recently, transmitter faults in your local area. Electrical interference. There are differences between a reception problem and one caused by electrical interference. See our help guides which explain the differences. If it is potentially interference, your landlord or management committee can contact the regulator, Ofcom, for help with solving the problem, using their contact web form.

Since it is a communal aerial, you will not be able to contact Ofcom directly. Your television can sometimes receive signals from more than one transmitter, which may be transmitting different regional news. This is more likely to occur following a retune of your television. To ensure you are receiving the correct regional news programmes from the transmitter your aerial is pointing towards, you will need to do a manual retune.

Please see our help guide on a manual retune. Please be aware most local news is not currently broadcast in HD at this time so will not be available on HD channels. Please use our Transmitter tool to see if you are in coverage. Following a decision by the Government, some channels used by Freeview, are being reallocated to allow for the future development of new mobile broadband services.