| Note that an amplifier can only amplify what's there. It's always better to use a better aerial located above the roof instead. The amplifier must always be near the input end of a long cable. If you put it at the output end, you are simply boosting the signal and the noise it has picked up, so you are hardly any better off!
An amplifier's ultimate performance is limited by the cable quality. We recommend CAI approved WF100 coaxial cable. 
C12537 masthead amp | Will an RF amplifier improve my signal/picture? Try it without! Connect your equipment with just a short length of coaxial cable. (Take the TV into the loft if necessary). If it still doesn't work, then an amplifier won't help. | | The main purpose of an amplifier is to counteract losses in a long cable. The second purpose is to allow you to split the signal without incurring losses. The third purpose is to get the Freeview signal level above the tuner "threshold" without swamping it with analogue signal. If your Freeview receiver works in the loft but not downstairs, you probably need an amplifier to overcome the signal losses in the cable. If the Freeview receiver does not work in the loft, try an amplifier. It may just boost the signal enough to overcome what's called the "tuner threshold". (This is often expressed as a negative figure like "-80dBm". The larger the negative number, the more sensitive the tuner). If you can't get the Freeview receiver to work in the loft, connected by only a short length of cable to the aerial, with an amplifier, then the aerial signal is no good. You may be able to improve it by aligning the aerial better, by raising the aerial higher, or by fitting a better aerial. For masthead aerial amplifiers see page 11c. 
aerial
signal | amplifier | amplified
signal | cable attenuates signal | T = tuner threshold |
A digital tuner has a critical "threshold". If the signal (yellow) is below this level, the tuner will not "see" it. So an amplifier will help if you can boost the signal above that threshold without also boosting the noise (shown in blue) above it. We sell a lot of variable gain masthead amplifiers for this reason. You can set the fine balance between not enough signal and too much noise. For UK Freeview there is an additional problem. While analogue TV transmissions continue, you must keep the analogue signal low enough to avoid "swamping" the digital tuner. For this reason, a correctly adjusted digital signal is likely to register 75% or less, otherwise the analogue signal (typically 14dB higher) will "blind" the tuner. A (low-noise) amplifier can be useful in some circumstances. But, if the gain is not adjustable, it's wise to connect an adjustable attenuator at the input of each Freeview receiver. Look at the table of cable specifications mentioned above. 860MHz is near the top end of the frequency band used for TV transmissions in the UK. You will see that 100 metres of WC100 attenuates a signal at 860MHz by 18.7dB. That's 0.18dB per metre. So you would need an amplifier of approximately 18dB gain to compensate for 100m of WC100 used for an RF connection. Or 6dB to compensate for 33m. The amplifier must always be near the input end of the cable. If you put it at the output end, you are simply boosting the signal and the noise it has picked up in the cable, so it's not as good. | 
T140 Global amp | What does a SkyLink compatible amplifier do? It provides a 9 volt supply for a "magic eye" remote extender and also passes the remote control signals back to the Sky Digibox. See page 3 for a choice of remote extenders. See page 15 for a choice of SkyLink compatible RF amplifiers and Loft Boxes. (A SkyLink amplifier should not be connected directly to an aerial as its noise figure is usually too high.) |
| Where does a booster go? | | | 
| The low-noise amplifier/booster must always be near the input end of the cable. If you put it at the output end, you are simply boosting the signal and the noise it has picked up, so you are hardly any better off! The purpose of an amplifier is to compensate for signal loss in the cable before it happens! NEVER plug a booster in the downstairs feed from the aerial. The only time a "set-back amplifier" or booster should be used downstairs is when it's amplifying the signal to send it somewhere else via a LONG cable (bedroom, kitchen, conservatory). Also see our "I live in a flat" example, below. | | Note that current flows up the "drop cable" to the amplifier so the cable must not have any poorly made joints. If there's a wall-plate socket, it must be a "DC pass" type. There are two types of amplifier: 1. The low-noise* masthead amplifier which can boost the faint signal from an aerial while adding the minimum amount of unwanted electrical "noise". This type is normally installed on the aerial mast or in the roof space close to the aerial. Ideally the cable between the aerial and masthead amplifier should be 1 to 2 metres long but a little longer will be OK. The masthead amplifier receives its power through one of its outputs - usually any one of its outputs. The power supply unit (PSU) will provide between 5 and 25 volts DC, dependent on the amplifier design. More modern low-noise amplifiers tend to use a very low voltage PSU. The power supply can be located near any convenient mains power socket since the length of coaxial cable between the PSU and the aerial doesn't matter. (The voltage drop will be immeasurably small). *Beware so-called "aerial amplifiers" with noise figures above 3dB (or not even mentioned). These are often cheap, pretty boxes sold in DIY shops. They may not give truly professional performance. Apart from adding too much noise to the signal, they may also introduce harmonic interference, causing "picture dropout". 2. The "Set-Back" amplifier which is used to boost the fairly strong RF signal from your receiver to another TV set. You can buy multiple output types called "distribution amplifiers". We recommend you use the T120/T140/T180 range. This type of amplifier normally includes a power supply and may be designed to plug directly into a power socket. A "Loft Box" combines both types of amplifier. It has a low-noise masthead amplifier as well as a distribution amplifier inside. Note: the Amplifier should have enough "gain" to overcome the losses in the cable it is feeding. See notes above about this. For example, assuming good quality cable like WC100 which loses about 0.18dB/metre at high UHF TV frequences, a cable length of 39 metres will lose 7dB of signal. So the amplifier gain should be roughly the same (7dB). Over- or under-amplification can result in a poor picture that may be "grainy" or have interference lines. Short lengths of cable (less than 20m) probably won't need an amplifier unless the aerial signal is really weak. The cable from the power supply to the amplifier has to carry a low current, low voltage supply. This is not dangerous but it needs a DC path so you must NOT use a wall plate or connector which "decouples" (removes) the DC path. All of the TV wall plates that we stock are proper DC coupled types. An attenuator may be required at each receiver where the cable run is short or the amplifier gain is too high. See our "Piping TV..." eBook for details. Where does a masthead amplifier go? | | 
| Low-noise masthead amplifiers are also available with two or more outputs. Sometimes these outputs are provided in the amplifier itself and sometimes they are in a separate power supply. These are handy where, for instance, you want only Terrestrial Freeview in each room. If you also want satellite TV in each room, a Loft Box might be more appropriate. | | 
| Another example where a two-output masthead amplifier is feeding two TV sets via Freeview boxes. Note that an attenuator must be fitted to any aerial input where the signal is too strong due to short cable length. You can calculate, as explained previously, on the basis that 1 metre of WC100 cable loses 0.18dB of signal. Note that current flows up the "drop cable" to the amplifier so the cable must not have any poorly made joints. If there's a wall-plate socket, it must be a "DC pass" type. | | 
| WARNING! Are you using a wall plate that looks like this? Read why you should replace it, click HERE.
| | 
| "I live in a flat. The signal is fine for my Freeview integrated TV but I need to feed the signal to the bedroom. If I fit a splitter, the picture breaks up!" Answer: Fit one of our set-back amplifiers. This splits the signal but boosts it at the same time. You should also fit a 6dB attenuator to the nearest TV aerial input if it doesn't require the extra boost. If the bedroom TV is not far away, it may also require an attenuator to avoid overloading (which can cause picture break-up just like insufficient signal). We offer high-quality 2-output and 3-output set-back amplifiers. 
|
Where does a distribution amplifier go? | | 
| A distribution normally goes in the loft as this is the most convenient place for connecting the signal to bedroom TVs. But there are many possibilities. A low-noise masthead amplifier may be required if the aerial signal is too weak to travel down a long "drop cable" to the main room. A set-back amplifier may be required if the cable run up to the distribution amplifier is very long. The gain of the distribution amplifier is usually only around 6dB to send the signal down the cables to the bedrooms. An attenuator may be required at the end of short cables. | | The Digibox output is added to the aerial signal for distribution to other rooms. (The Digibox requires an RF modulator in order to combine signals like this, otherwise the aerial signal will simply pass through without having the currently selected Digibox channel added. (The "Digibox" can be any sort of equipment - Satellite, terrestrial or a player. Several may be "daisychained together" if required, but all must have internal or external RF modulators.) |
|
| 
| Piping TV Around the House The eBook explains the above concepts in greater detail, giving wiring layouts that you can use or adapt to suit your own property. Covers amplified splitters, Loft Boxes, "magic eye" remote extenders, amplifiers, attenuators, cable, and avoiding interference. http://www.The-Cool-Book-Shop.co.uk |
 | Installing Sky Digital TV Companion book to our free "Understanding..". Essential reading if you want to move your old dish system to a new house, install a brand new Sky-Plus or standard dish system, fit a dish system to your house, apartment block, motorhome, caravan or narrow boat or use it in Europe, this book answers your questions. What size dish, what sort of cable, connectors, which receiver is best for outside the UK ... 120+ page book filled with colour photographs and easy-to-understand explanations. I guarantee you'll be delighted with this amazing book full of information! Installing Sky Digital TV FREE BONUS BOOK!: UK Digital Satellite TV in Europe
When you download "Installing..."
Includes tips on receiving ITV in Europe. |
