Freeview Aerial Requirements

Introduction

In order to receive Freeview you need an appropriate aerial. You may be able to use your existing analogue aerial, or you may need to change you aerial.

Why would you need to change your aerial?

There are several reasons why an aerial upgrade may be required, including:

• You are using a local repeater for analogue reception
  A local repeater receives the analogue TV signal from the main transmitter, then broadcasts is again on a different frequency to a small area which would get poor reception from the main transmitter. This is common is towns and cities, where there is a signal shadow, e.g. caused by a hill between the transmitter and the town. Many of these repeaters will not repeat the digital signal. Often repeaters require your aerial to be vertically aligned (i.e. with the spiky bits sticking up and down), wheras most main transmitters require your aerial to be horizontally aligned (i.e. with the spiky bits sticking side to side).
• Digital TV is broadcast on a frequency for which your aerial is not designed
  Some aerials are designed to cover narrow frequency ranges, only part of the frequency range allocated for TV transmissions. This allows more gain (which gives better reception) over that frequency range. These aerials are often referred to as "narrowband". Analogue transmissions are grouped together so that a narrowband aerial can be used to receive all channels from a single transmitter. When digital was added, it was not always possible to place the digital signals in the frequency range. This means that your current narrowband aerial may not give sufficient gain to receive the digital transmissions. In such cases a change to a "wideband" aerial (one that is designed to receive the entire TV frequency range) may be necessary.
• Digital TV signal is too weak for your current aerial
  Analogue TV degrades slowly with poor signal conditions. If you have a weak analogue signal you may notice more noise (speckles or snowy effects) or interference. Digital TV degrades much more rapidly, and tends to either work well or not at all. If you have poor analogue reception, you may need a better (higher gain) aerial to receive digital signals. A signal booster may help (particularly if it is close to the aerial), but may just amplify your existing noise.

Will My Current Aerial Work?

There are 4 things to check which will give an indication of whether your current aerial will receive digital signals. If all of these are OK, then you stand a chance of receiving digital signals with your current aerial. If any one is not OK, then you will probably need to upgrade your aerial.

1. Check whether you can receive Freeview in your area using an online postcode checker such as the one on the DTG website. Enter your postcode - if you can receive Freeview, then click on the "Tell me more" link and it will give details of the compass bearing to your transmitter and the aerial group (A, B, CD, E, K or W) and polarisation (horizontal or vertical). Make a note of these details - we are about to check whether your existing aerial matches these.

2. Check whether your aerial is pointing the correct direction. Get a compass and check whether your aerial points the same direction as the compass bearing given on the DTG we site. If you don't have a compass, you can get a rough idea by the position of the sub. The sun rises at around 90 degrees (east), should be at about 180 degrees at noon (south), and sets around 270 degrees (west). Note that using this technique is only useful to tell whether your aerial is point in the rough direction of the transmitter - it is not suitable for aligning the aerial. Alternatively, if you have neighbours that can receive freeview, compare your aerial direction with theirs.

3. Check the polarisation of your current aerial by looking at the spikes that stck out of it. They should either point side to side (horizontal alignment) or up and down (vertical alignment). Check that this matches the alignment given on the DTG web site.

4. Look at the coloured bung on the end of your aerial (the end pointing towards the transmiter). This should be one of the following colours, which identify the aerial group (or band).

If your existing aerial covers your digital group (e.g. if your existing aerial has a red bung, it is a group A aerial. If the DTG website identified that you need a Group A aerial to receive digital than your current aerial may be OK, otherwise you'll need a new one. See the following table for a list of bung colours that may work fro different aerial groups:

If all of these checks are OK, you may be able to receive digital TV with your current aerial. Try to borrow a receiver from a friend and try it out. If you can't, you could buy one, but be prepared to spend money on an upgrade.

What Can You Do?

The best thing to do is to consult a local aerial specialist. Using one recommended by someone else if probably a good bet. Alternatively, the CAI (Confederation of Aerial Industries) has a databases of CAI members, who are professionally qualified and independently monitored.

You could choose to install a new aerial yourself, however before taking this decision, make sure you are fully aware of what you are taking on. It may involve high heights and the use of ladders. Make sure you take any necessary precautions to protect yourself. Aligning an aerial is tricky without a signal meter. The bars on your Freeview receiver are not usually good enough for this job.

The CAI also benchmark aerials, and rate them into standards. You could use this information to help choose a new aerial. See the CAI website for details of how this works and information about the aerials that they have tested.

DIY Upgrade

Firstly and most importantly, keep yourself safe. No amount of TV, digital or otherwise, is worth risking a serious injury for. Consider getting a professional in instead.

Still reading? OK - Consider where to position the new aerial. An external roof mounted aerial will give far superiour reception over an aerial mounted in your loft, but is usually more difficult to install. Also consider whether you can reuse the exising coax aerial lead. You may want to replace this with a high quality coax for better signal reception.

Use the DTG web site to find the direction, aerial group and polarisation. Purchase an aerial to match the group. If you are a long way from the transmitter you'll need an aerial with higher gain. If you are close to the transmitter then a lower gain aerial will be lighter and easier to install.

Use a compass to get the bearing on the transmitter. It is important to get this accurate, particularly with high gain aerials. Align the spikes on the aerial according to the DTG website (side to side for horizontal polarisation or up and down for vertical polarisation).

Once you've mounted the aerial and cabled it, you can test it out. Most receivers have crude signal meters which can be used to fine tune the position of the aerial - get a friend to help here shouting when the meter goes up or down. Once you are happy, tighten all adjustments on your aerial to ensure that it will not move.

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