Why Are TV Aerials Installed On Top of Houses/ Buildings?

July 3, 2019
by
Tom

Why Are TV Aerials Installed On Roofs?

 

If you wanted know know why TV aerials are usually installed on roofs, chimney stacks and high up on walls – often on very large aerial masts. Read this article for all you need to know.

 

TV and radio aerials both receive their signals from land based transmitters, unlike satellite dishes which receive their signals from satellites in space. This means that nearby trees and buildings can get in the way between your property and the transmitter itself which will most likely block much of the signals reaching your property, unless you live very near the transmitter itself in which case you may get away with an indoor aerial or aloft aerial. But more often that not it is much better, or completely necessary to install an aerial outside on a chimney stack or on a aerial pole on the exterior of your property.

 

Installing Aerials High Outside Maximises Signal Strength 

If you install your aerial outside you’re most likely to maximise the signal being received on your TV aerial for a more reliable reception that is less likely to break up and pixelate. This is because by installing aerials high on properties so they can clear nearby obstructions like trees and other buildings in your aerial less of the signal will be blocked from reaching your TV aerial. If you can get line of sight between your TV aerial and the TV transmitter you’re likely to have a very good TV or radio signal. Plus the aerial alignment is also likely to be very easy as you can just point the aerial with your eyes and are not likely to need any specialist aerial alignment tools.

 

Although it is recommended to install your antenna outside care needs to be taken so that you do not overload your TV tuners and distribution equipment with too much signal if you live in a strong signal area. This is usually easily resolved with an attenuator but you may want to opt for something like a log periodic aerial instead of a high gain aerial to help avoid this. 

By installing aerials high up outside of your house, as you're maximising your signal strength you’re also much less likely to need a TV aerial amplifier to run multiple TV points. As a passive splitter will often be fine. This is because you can often afford to lose a bit of signal through the splitter because the TV aerial has been installed in a position where the signal is strongest.

 

Every Extra dB of Signal Received Creates A More Reliable/ Robust Signal

If you know how to measure the TV aerial, satellite and terrestrial radio signals you will already understand this comment. If you don’t a quick brief is TV aerial signal strength is usually measured in dB with reference to micro-volts. The absolute minimum for a digital TV signal like is used for Freeview and Soarview is 45dB but you should aim for no less than 50dB. If you’re receiving less than this you will want to install the aerial higher up where the signal is strongest, maybe of a larger aerial pole. Install a higher gain aerial and/or a masthead amplifier to help give the signal a boost and overcome the signal losses associated with the connecting coaxial cable. Now the signal strength is just one measurement that we are concerned with. The next is the signal to noise, or carrier to noise. This is the relation between the actual received signal and unwanted noise in the signal. You could for example receive a respectable 60dB of signal strength from your antenna but have an interfering signal of 40dB on the same frequency. This means that you only really have a signal strength of 20dB and this isn’t very good, this is called the carrier to noise ratio. All equipment measures this differently but I recommend if your equipment has it to pay attention to the Modulation Error Ratio (MER), this allows you to look into the signal itself and gives a more reliable measurement. I will discuss this in greater detail in another blog so that’s all I will go into it here but in theory every extra dB received from your TV aerial potentially will be added straight to the carrier to noise ratio creating a more reliable and robust signal.

 

It Gets The Aerial Away From Many Local Sources of Interference 

By installing your TV aerial high, up on your roof or wall you are maximising the distance between potential sources of interference and the TV aerial itself which could potentially pick the interference up and feed it back into the TV system which could cause poor TV reception. In todays wireless world there are many potential sources of interference which could cause the TV picture to fail. Typically, they fall into the following categories. Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI). All things like wireless equipment such as routers, phones, computers all can potentially interfere with your TV signal, as well as sources of impulse noise like timed circuits, car ignitions and so on. Installing your aerial high up and away from these sources minimises the chances that the could ruin your TV reception. It doesn’t mean that you won’t get interference on your TV signal as you could also pick this up from nearby TV/ telecoms transmitters with known interfering sources being 4G, Tetra and co-channel interference among others.

 

To help minimise interference induced into the TV signal I recommend the following, installing a double screened coax cables. This will help stop interference penetrating onto the cable itself. An aerial with a balun, this will help remove any interference absorbed by the coaxial cable screen from feeding back into the TV signal at the aerial and balances the system. Install all screened coaxial cable connectors like F connectors and cable terminations within a metal housing like is used in screened wall-plates. To add to this you may also want to an aerial type designed to filter certain types of interference, install the aerial high up as suggested in this blog and an appropriate TV aerial filter to remove unwanted signals that have been picked up by the TV aerial. If you do all of this you should never get any problems with your TV aerial reception.

 

Installing Aerials On Walls Vs Installing Aerials On Chimneys 

If you have decided that you want to install your aerial high up outside, you may be wondering whether it would be best to install it on the wall or on the chimney. There are pros and cons to both of these.

Chimneys Are Typically The Highest Point

More often than not the chimney would provide the most height so that’s why most aerials are installed on chimneys. That being said if you have a gable end wall where a chimney could be mounted you may be able to get more height here.

 

Installing Aerials On Chimneys Is Less Noticeable

Installing aerials on chimneys typically is more discreet, most people expect to see aerials there and typically you will only need no larger than a six foot mast, you may need a larger pole for equivalent height when mounted aerials to walls.

 

Installing Aerials On Chimneys Is More Difficult

Installing aerials on chimneys typically is harder, this is because there is more skill involved in installing a chimney lashing bracket than drill fixings like are used for aerial brackets. If you’re wondering why wall brackets and drill expansion fixings are not used for mounting aerials onto chimney stacks. This is because most chimney stacks are only one skin of brickwork, which is often in poor condition. With wind loading and drill fixings you’re running the risk of pulling bricks clean from the chimney in high winds, which I have seen several times before. Instead we install a chimney lashing bracket or chimney ratchet strap which wraps around the chimney and the tension of the wire holds the aerial in place.

 

Chimneys Are More Difficult To Access

Accessing your chimney may be more difficult that you think. If you live in a bungalow this may not be very tricky but if you live in a normal style house, it is likely that you will need a ladder to get up to roof height and a cat ladder to roll up the roof and hook over the chimney ridge to access the chimney. If you do not own one of these but do a normal ladder you may just want to mount the antenna on the wall instead.

 

Could Break Roof Tiles

Sometimes when I arrive at jobs and the roof is in poor condition and/or the roof tiles are “biscuit” tiles which are the type where they are very easy to break and there is nothing that can be done without breaking the tiles when accessing the chimney. I will often just try to avoid the chimney altogether and install the aerial on the wall or in the loft instead. There is nothing worse than stepping off a ladder onto your roof ladder only to hear a few tiles go under your feet.

 

Walls Are More Suitable For Larger Masts

If you need to install a 10’+ mast I would recommend installing the aerial on a gable end wall if possible. This is because the wall itself is usually far stronger than the chimney stack. With T and K wall brackets a large bracket spacing can be created making for a every strong fixing more suited to larger aerial poles. Providing the chimney stack is large enough a similar fixing can be achieved with double lashing brackets but I don’t like installing anything larger than a 10’ mast of a chimney stack, ideally not larger than 6’. Of course you will need a gable end wall for this to work, if you do not have one and live in a terrace house for example you may find that a 4’ mast on a chimney stack offers more height than a 16’ mast on the wall.

 

If you have hanging tiles on your walls you may find that you have to install your aerial onto the chimney stack or another position as this would prevent you from fixing the brackets to the wall.

 

Other Places Where Aerials & Antennas Can Be Sited

You could install your aerial fixings on a fascia bracket or non-penetrating roof mount. If you’re looking for other places to mount a TV aerial instead of a wall or chimney I recommend reading our previous blog on alternate positions to fix your TV aerial.

 

Do Radio (FM & DAB) Need To Be Installed Outside?

It’s not a bad idea to install your FM or DAB aerial outside with your TV aerial, especially if you live in a weak signal area as this will help maximise the radio stations you can receive. Often the extra height works wonders and you can get away with an omni aerial which receives signals in all directions. Directional radio aerials will help get some more signal strength but alignment can be more difficult.

 

It’s is also important to note that DAB uses a lower frequency than TV aerials and FM again even more so. This means that they are not as affected by obstructions like buildings blocking the signals and means that often a good signal can be achieved with an indoor aerial or an outside aerial installed in your loft. If you’re using an external aerial for your radio tuner you need to make sure that your tuners has a connection for this. Many manufacturers like Bose do allow for this but you may need to but an adapter to connect an external radio aerial.

 

Is An External Likely To Get Hit By Lightning? 

An external aerial is much more likely to get hit by lighting than an indoor aerial, but this is actually very, very rare. It doesn’t happen often. Many buildings in fact connect the outdoor antennas to the lighting protection system. If you’re concerning about such things a larger metal pole installed may not be a good idea and you may want to install an aerial in your loft, providing you have enough signal to do so that is.

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