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. You have to remember that Yagis were originally designed as single frequency aerials. Thus if you really need a high gain aerial and are able to use a grouped antenna on your transmitter, a grouped aerial is always preferable.
This is particularly true in the case of the A group , but also to a lesser extent K group and B group transmitters. Gain is measured in decibels or dB [this is a logarithmic scale] and for aerials it should be measured as dBd , which is the increase in signal received from an antenna compared to that which would be measured from just the dipole on its own. Note that 0dBd does not mean that zero signal would be received by the aerial , it just means that the aerial only picks up the same amount of signal as the dipole would on its own, i.
In fact the vast majority of FM and DAB aerials are just dipoles which therefore only have a gain of 0dBd yet they work fine in most cases. Always remember that there is more than one way to measure gain, e. Our Guide to TV Antennas Before you dive into our guide, do a coverage check to see what antenna is best for your address. Which antenna should I use? Each antenna provides a different viewing experience: UHF Aerial will give you better pictures, sounds and more channels especially local channels than Satellite.
Satellite Dish will give you a smaller selection of channels and standard definition broadcast. Indoor Digital UHF Aerial If you can't get a roof-top aerial installed, you may be able to use one of these if you're within 5km or have a line of sight to your nearest transmission site.
Satellite Dish What is a Satellite Dish? Not sure which antenna you have up there? Here are some simple things you can do to check what you have on your roof: Pop outside and look on your roof: If you live in a house or unit, have a look on your roof or high on the side of your building to see if there is an antenna up there. If you have something that looks like one of the above, you're good. If you are in a shared building like an apartment block, best to check with your building manager.
Connect the cable: Plug it into the back of your TV and try tuning in. You can find general tuning steps here. No worries! Keep your TV antenna away from metal Keep in mind that metallic surfaces near your antenna can cause interference with the digital signals and can even block your reception. For example, when placing your antenna in a window, even metal burglar bars in your window can cause issues metal blocks both TV and Radio signals. Try to keep as much distance as practical from metal objects 6 feet or greater is ideal.
Strong signals areas If the signal strength in your area is really strong and you are using an antenna with built-in amplifier it might be possible that the TV receiver gets too much signal.
This might reflect in loss of TV signal. The amplification of the antenna can be reduced by turning the variable gain control from max to min. Put it on min and scan for TV channels again. Telescopic antennas If you are using an antenna with telescopic antennas make sure that they are extended to the maximum length to get the best performance.
Longer cable Extending the antenna cable will slightly reduce the signal level that gets to your TV, but if the longer length allows you to reach the window that is facing the TV transmitter it might improve your TV signal.
Try not to use an unnecessarily long cable though, as that will reduce your signal level. Cables other devices Keep all other wires and cables as far away from the antenna as possible. The close proximity of other cables can interfere with the reception. Amplified antenna Adding a signal booster to your antenna, or using an amplified antenna can give you better results than a passive antenna.
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