How to fit your own Digital Aerial
Aerial Installation Advice
Safety first
Firstly you must consider your safety. A competent and safety conscious aerial installer will secure their ladders, tying them to a wall using eye bolts and ratchet straps. Anybody who hasn't had the appropriate training or experience should not attempt to climb a roof, as it can be extremely dangerous!
Aerial selection
The digital aerial that you require will depend on where you live, the closer that you live to a transmitter the lesser gain aerial you will need. If you are located in a fringe reception area then you will need a high gain digital aerial.
Do consider the construction of your aerial. Cheap aerials usually have pressed alliminium rods and will break in high winds or if birds land on them, which they do! I would recommend using aerials with solid rods and a solid boom arm. Aerial shop
Aligning your aerial
You can do this by looking at other aerials on houses close to yours. Most digital aerials and old analouge aerials recieve their signal from the same transmitter. Most aerials will cope with 10 degrees +/- of ideal without significant signal loss.
Aerial mast
Height is probably more important than the aerial. If you are in a low down aera then use as tall a mast as possible. Do not over-tighten the U bolts used to secure the mast to the bracket. If you do feel the need to over clamp then do it on the bottom U bolt. Over-tightening the top bolt may cause the mast to kink and then bend in high winds.
Bracketry
Be sure to fix your mast securely. Avoid the top five courses of bricks if securing to a gable end. Choosing the right bracket will depend on your mast and aerial.
If you have a lightweight aerial and a small alloy mast then a bracket equal to 10% of the size of the mast will probably be adequate, however a tall steel mast with a large aerial will probably need a bracket spanning at least 25% of the mast size. Aerial shop
Cabling
Good quality digital cable is recommended. Old existing analogue cables can sometimes be used but can often suffer from substantial feeder loss. Splitters and old face plates can also cause problems. You can easily lose a good signal if you then try to split it. If you have a good signal and then put a splitter in you may then drop the signal strength too low. Weak analogue pictures deteriate in quality but digital pictures disappear alltogether if they are too weak.
Signal strength at TV/Reciever
An acceptable signal level for digital TV is far narrower than that required for analouge TV. You ideally need an RF level of between 50db to 65db of digital signal strength
The quality of the signal is also critical, your reciever must be able to understand the binary code that is being broadcast. Things such as mobile phone masts can often scamble a digital TV signal
Amplifiers
Amplifiers should only be fitted when a digital signal has good quality but a low RF level. You cannot boost what isn't there
Amplifiers should be fitted as close to the aerial as possible, ideally about 1m to 2m from the aerial, this type of amp is called a mast head amplifier.
Loft distribution amps are ok to distribute a signal but an acceptable signal will usually be needed to start with at input
Low noise input amps should always be used. Otherwise you can boost a signal but scramble it at the same time. Cheap amps tend to create about 6db of noise, good quality amps create below 3db on noise.
Conclusion
If you understand all of the above and have the knowledge and equipment to scale a roof, then fitting your own aerial may be a cost effective option
However if you have to hire ladders, risk buying the wrong equipment and are not sure what you are doing then paying an aerial installation company will probably be a cheaper and safer option!