Guide to Selecting the Right Antenna

First up - you will need three pieces of equipment to improve your mobile signal: - an antenna - a cable and - a connector.

Similar to your TV, mobile phones and wireless broadband modems connect to antennas.

1 - For increased signal, the best position for your antenna is as high as possible outside your car or house - this means you'll need cable to cover the distance from where you want to put the antenna, to where you want to use your phone or modem.

2 - You'll need something to connect your cable to your phone or modem - all good quality modems have an external antenna port, meaning all you'll need is a small adaptor cable called a patch lead to go from the big connector on the cable to the tiny connector on your modem.

Many phones have an external antenna port, most notably Telstra, Samsung, and Motorola brand phones. You'll just need to use a phone cradle if your phone does not have an external antenna port.

If you don't like the idea of having to constantly tether your phone to a patch lead or cradle, you can connect your antenna to a smart repeater which will amplify and broadcast your antenna's signal throughout your house at full strength - this will give your mobile phone a full five bars.

There are four main factors that reduce mobile coverage:

• Distance from the cell tower

• Terrain

• Dense vegetation & buildings

• Your house

Distance

You're probably not too surprised to learn that mobile signal is reduced by distance (due to the Inverse-Square Law) from the cell tower, causing a gradual weakening of signal.

On flat terrain, most cell towers have a usable range of about 40km before you'll need to use an external antenna. With a good quality external antenna it's possible to receive signal as far as 120km.

Terrain

Radio waves diffract by nature - this means they can bend over hills and around structures/objects, so being able to see a cell tower is not the ‘be all and end all’ of obtaining signal.

If you've travelled through hilly areas, you've more than likely noticed you still have mobile reception, despite being in a small dip or behind a rise in terrain. It's large or sudden changes in terrain that will significantly impact phone coverage – in this type of scenario, height is the key success factor.

Vegetation

Dense sections of trees are notorious for diffusing signal - one or two trees will not impact signal strength too much - add more and more trees, and it's a little like 'death by a thousand cuts, with each tree absorbing and deflecting a small amount of signal.

The best way to mitigate this phenomenon is by increasing height to minimise the path that signal must pass through offending vegetation.

Building penetration

Mobile signal is reduced when passing through buildings, trees, water, and even the air we breathe. The worst offenders are thick and conductive materials such as concrete, metals and foil-based insulation – this is often why signal can be weak indoors despite a strong signal outside.

For a comprehensive look at all the factors involved, have a read through our Poor Coverage Explained guide.

OK let's get started 

Step 1 - What network am I on?

This seems a simple question to answer - and for some networks, like Telstra - it is. However, what we really want to determine, is what frequency the network operates on in your area.

While there are countless mobile network operators, there are only three mobile networks operating in Australia - Telstra, Optus, and Vodafone.

Use our Coverage Maps to determine what frequency your network is operating.

This table is a quick guide.

Australian Carrier Frequencies

Step 2 - Where am I?

Different antennas are designed for different situations. So identify where you're trying to improve service - the house? car? boat? Are you in the one location, or are you moving around?

Rather than talking about antenna types and gains, this guide will work through the best antennas for your house, vehicles, and marine vessels.

The house or office

The best place to start is often by performing a quick self check. Walk around the house – is there a particular spot where signal is good? Walk outside the house or on to the street – does the signal improve?

Climbing up on your roof can give you an idea whether height is an important factor in improving signal. [The appropriate safety gear should be worn at all times when working at heights - getting a good signal is not worth a broken leg - eek!]

OK, now you need to work out where the nearest Telstra tower is, and how many towers are in the area. You can find this out by following our Guide to Locating a Phone Tower.

If you're still not sure, book in for a Detailed Site Assessment where we can look after everything for you.

Indoor antennas

If you're on the move or don't have the room to mount a roof antenna, an indoor antenna is a convenient way to improve mobile phone service or wireless broadband speed.

While the much smaller dBi gain reduces strength, it allows indoor antennas to receive from many directions - with no need to fiddle around to find the optimal direction - they're perfect if you're moving around or don't know where the best cell tower is located.

If you've noticed your signal strength is usually stronger next to a window or doorway, then this is often the best place to put the antenna.

One of our most popular models is our 12dBi window mount antenna - its adhesive stick on mounting makes installation easy.

Roof antennas

Most issues with slow wireless broadband or bad phone reception are solved with a roof mounted antenna. If you've located your nearest cell tower, the next step is simple.

There are two main types of roof antennas - directional (Yagi) antennas and omnidirectional (collinear) antennas.

Directional, or Yagi antennas, are the most popular choice of antenna, as their high power provides the strongest increase of all antenna types.

The trade-off here is that they require aligning in the direction of the cell tower - the higher the dBi gain, the more precise you'll have to be.

In deciding between Yagi models, wider angled 12-14dBi antennas are more suited for hilly areas, while the 15-16dBi antennas are better for very long range connections, with less hills in the way.

Omnidirectional antennas are designed for areas around town or in the suburbs where there are often several cell towers within range. This antenna lets your mobile decide which tower offers the best signal. However, as omnidirectional antennas spread their power over a 360° range, they don't receive signals as strongly as their Yagi counterparts.

There are typically three Yagi antennas we recommend for different areas depending on their terrain type and distance:

• 12dBi LPDA Yagi: Short Distance (1-15km) or Nearby Hills (1-5km)

• 14dBi or 15dBi Yagi: Moderate Distance (15-30km)

• 16dBi Yagi: Long Distance (30-70km) or Flat Areas (hills > 15km away).

The car

Choosing an antenna for your vehicle usually isn't too complex. All car antennas receive signal from all directions, and follow the same principles as a UHF aerial.

The choice of antenna depends on the area you're travelling through. A higher gain means a stronger signal, however, when you increase an antenna's gain (i.e. its dBi), the angle it can receive from is reduced.

This means that high gain antennas are more suited to flatter areas, and moderate gain antennas (such as a 5-6dBi) are better suited to hilly areas.

Choosing an Australian made antenna is your best bet - brands such as RFI and ZCG Scalar are high quality and extremely durable, and they're specifically designed for the tough Australian environment. They have a more sophisticated internal design, allowing most models to operate on multiple mobile networks.

Around town

Built up areas often have several cell towers within a few kilometres, and are usually mounted on tall monopoles or on top of hills.

The antenna of choice for many fleet and commercial vehicles is the 5dB RFI CD1250 or the 6.5dBi RFI CD7195 (formally 2195).

General highway and travelling

If you're after a versatile antenna capable of functioning in a range of different terrains, the 6.5dBi RFI CDQ7195 and 7.5dBi RFI CDQ7197 (formally 2197) are the antennas of choice for all Australian networks.

Outback QLD & WA

For flat outback areas the clear choice is the ultra-high gain 9dBi RFI CDQ7199 (formally 2199)

We often hear of customers purchasing falsely advertised 9dBi antennas - as a general guide a 7dBi antenna should measure about 1.1m and a 9dBi antenna should measure about 2m in length.

The boat

Marine antennas are typically high gain omnidirectional antennas (6-9dBi), to allow maximum off shore range no matter which direction your vessel faces.

Selecting an appropriate antenna depends on the type of vessel you have, and how far off shore you plan on going.

As a simple rule of thumb: the higher the antenna gain, the further off shore you can go. 8 or 9dBi marine antennas can easily extend your range past 120km off the coast. However, because higher gain antennas have a smaller angle in which they can receive signal, smaller vessels that sway side-to-side, may be better with a slightly lower gain, (such as a 7.5dBi) antenna, to compensate for the motion.

In practice, this is generally not an issue for most vessels as the receiving angle is a 'half power' measure, which means that if your boat was to swing past the quoted angle, the received gain would be 3dB less (half the power in Watts) - the same as a lower gain antenna.

Here are some we recommend: - ZCG 8.1dBi Deck Mount Antenna - ZCG 8.1dBi Mast Mount Antenna

Antenna gain

The first step in understanding antenna gain is that your phone or modem's internal antenna gain is typically 15 to 0dBi. So any good quality external antenna usually provides immediate benefit regardless of stated gain.

The key here is quality. Quality is typically measured by electrical efficiency, pattern stability, and VSWR (Volting Standing Wave Ratio).

On the other hand, gain is how the antenna focuses the radiated power.

You might be thinking, why would anyone buy a 6dBi antenna when they can buy a 9dBi instead - and while it's true that a 9dBi has a higher gain, it doesn't always translate to better performance.

Different antenna sizes and types have differing three dimensional patterns in which they receive signal. This is referred to as an antenna ‘radiation pattern’, and is often measured in terms of vertical and horizontal beam width.

Beam width refers to the angle in which an antenna receives signal, and is measured in degrees from the horizontal axis.

In a perfect world, all antennas receive the same amount of signal from the surrounding atmosphere in the shape of a doughnut, where width represents physical distance, and height represents physical height.

Given that you've only got a certain amount of dough (signal) to make the doughnut, you can either make your doughnut tall and skinny or flat and wide (or somewhere in between). In terms of beam width, a tall doughnut has a larger vertical beam width, and a flat doughnut a small vertical beam width.

Different antenna types

Aside from differing in gain, antennas also differ in their type of build. Each different build offers a different set of advantages and disadvantages.

Omnidirectional antennas (Ground Independent)

These are the most common type of mobile phone/UHF/CB antenna - they have a 360-degree horizontal beam width, meaning they work in all directions.

This type of antenna does not require a ground plane to function, so it can be mounted with a small bracket on just about any surface and location.

Best performance is achieved by mounting the antenna as high as possible - to eliminate as much signal interference as possible.

Magnetic base antennas (Ground Dependent)

This is a type of omnidirectional antenna that must be mounted onto a metal surface.

Magnetic Base or Ground Dependent antennas are half the size of ground independent designs, because they use the metal surface they are connected to as the other half of the antenna.

This means that the size, shape and surface area of the metal object are very important in achieving the best possible result.

This ground plane follows the same principles as the antenna - a larger surface allows for a larger fraction of the wavelength.

Ideally a surface with a diameter greater than one wavelength (about 35cm for Telstra Next-G 850MHz) will perform best, smaller surfaces down to 9cm will produce acceptable results (quarter wave).

Magnetic base antennas also achieve a more compact design by incorporating one or more loading coils which help maintain resonance, improve the radiation pattern, and most of all make the antenna more flexible - these traits are important for vehicles with low clearance.

Magnetic antennas are ideal for vehicles; they also make great indoor household antennas when mounted on filing cabinets and windowsills. Their compact design means they're an ideal travelling companion.

Although designed for metal surfaces, this type of antenna can be used on any surface, but will produce a gain 3dB less than what is stated - for example, a 7dBi magnetic antenna on a wood surface produces a 4dBi gain.

Yagi antennas

The odd looking TV antenna on thousands of house roofs, is the most common example of a Yagi antenna.

As mentioned earlier, Yagi antennas trade their ability to work in all directions (omnidirectional) for an increased gain. This is achieved by putting an array of smaller 'director elements' in front of the actual connected element.

These director elements receive the incoming signal and re-radiate the signal until it reaches the driven element (the one connected to the cable).

Behind the driven element, is a slightly larger element known as a reflector - and it does as its name suggests - reflects the signal back to the driven element.

By increasing the number of director elements and length of the Yagi, we reduce the horizontal and vertical beam width - resulting in an increased gain.

For a 3dB (twice the power) increase in gain, we have to double the length of our Yagi. For these reasons, a Yagi will often max out at 16dBi (on 850MHz) before becoming impractical in length.

The Yagi 21dBi myth - don't let anyone tell you that there is such a thing - because there's not!

In order to accommodate 21dBi, the Yagi antenna would need to be over six metres in length and impractical to install - so they just don't make them!

Grid parabolic antennas

In comparison to the Yagi, Grid Parabolic antennas increase their gain by increasing their width.

This is sometimes a more practical option, as they do not require stabilising brackets or cross bars to hold the antenna safely in place.

This type of antenna works in the same manner as a satellite dish - the signal is reflected off the dish/grid and onto the small receiving element placed above the centre of the grid or dish.

If you'd like to learn more, you can read our Guide to 4G Antennas and MIMO