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ANTENNA TEST

 

HEAD

GLASS ACTS

 

INTRO

Cellphone aerials are bestowed with incredible powers, that magically increase range and reduce the number of dropped calls, or so some manufacturers would have us believe. We’ve been trying to cut through the static to evaluate some well-known brands, and see just how well they perform in real-world conditions

 

COPY

It’s exactly 100 years since Marconi’s first successful experiments with radio waves, but even after all those years antenna design is still something of a black art. If you need proof just take a look at the amazing diversity of cellphone antennas. They all do the same job. They all operate using very tightly specified transmission systems, on clearly defined frequency bands, yet rarely are any two alike.  In a curious sense that’s quite satisfying, it shows there’s still no such thing as the perfect antenna, and we’re not as clever as we sometimes think we are...

 

Nevertheless the underlying theories of radio propagation are well understood, and certain basic principles apply to all types of antenna design, but it’s the tantalising tweaks that squeeze out the last ounces of performance and efficiency that make this subject so interesting.

 

Part of the reason there’s so many different types of cellphone antennas is the wide range of applications. Over the coming months we’ll be looking at some of them in close detail. There’s a lot of ground to cover, from handset aerials to car body-mounted antennas, we might even get around to specialist cellphone antennae for marine and aviation installations.

 

However, we’re kicking off this month with one of the commonest types of cellphone aerial, the one most users are likely to encounter as an accessory purchase. That’s the glass-mount car antennas for analogue ETACs and digital GSM phones, operating over a range of  870 to 960 megahertz. They’re one of the most DIY-able of cellphone aerials, there’s no need to drill any holes in the car bodywork, and they can be fitted by almost anyone with a minimum of fuss.

 

Up until a couple of years ago glass-mount aerials were mostly supplied as part and parcel of a car kit installation. The customer normally had little choice about the make or style, but things are changing and they’re now widely available from the growing network of cellphone accessory dealers. Even if you don’t want to fit an aerial yourself you can at least make an informed choice. So what are the options?

 

AERIAL TYPES

There are two common types of glass-mount aerial: short (50-60mm) unity-gain or ‘1/4 wave’ models, and the longer (290-300mm) colinear ‘whip’ designs, which are usually denoted by their gain figures, (typically 3 or 4dB). We needn’t go into too much detail about gain, suffice it to say that it refers to way in which the aerial receives (and radiates) radio frequency signals. By making the aerial more sensitive to signals from a particular direction, (or directions), it’s possible to increase its efficiency, and as a consequence, the gain. That makes colinear aerials more attractive for basic hand-portable car-kits, which have lower power outputs, compared with purpose-designed car cellphones. Initially colinear aerials were dearer than 1/4 wave types, but these days there’s not a lot in it, thanks to the economies of scale. By the way, we’ve also included one odd-bod antenna in our roundup, to see how it compares with more conventional designs, more about that later on.

 

Some glass-mount antennas have what’s known as a built in ‘ground-plane’. Normally the metal of a car body acts as the ‘ground’, but as the antenna is mounted on glass, the ground effect is minimised. Short radiating elements or metallic strips connected to the outer sheath or shield in the cable, and bonded inside the mount or coupler, act as a ground, thus improving the antenna’s efficiency.   

 

DIY INSTALLATION

Fitting one of these aerials normally only takes a few minutes, running the cable is another matter, and this can easily take an hour or two, depending on the vehicle; even professional installers quake at the mention of some luxury cars. We must repeat the warning given in an earlier feature about DIY installation, don’t do it unless you’re entirely confident about your abilities. It’s mostly common-sense, and no more difficult than a car stereo, say, but pay a professional if you’re in any doubt.

 

If you want to have a go here’s a few top-tips: There are two parts to a glass-mount aerial, the outside mount, and the interior coupler. The exterior mount has the toughest job, and most care should be taken with this part. The best place us normally the rear screen. Mount the aerial as high up as possible, avoiding heating elements, and the path the wiper blade. The portion of glass it’s to attached to needs to be absolutely clean, and grease free. Most glass-mount kits come with an alcohol impregnated cleaning swabs, we’d recommend using them only after the area of glass has been thoroughly cleaned -- both sides -- with a water-based detergent, wiped clean, and then thoroughly dried. Some manufacturers also suggest warming the glass, especially if its cold, with a hair dryer, this helps to cure the adhesives. The mount and coupler must be perfectly aligned with each other, this can have a major effect on efficiency. Make sure the radiator is vertical, and well away from any metalwork, before it’s tightened.  

 

Most aerial kits come with a length of coaxial cable (4-5 metres), this usually has a plug on one end, which connects to the coupler module; on some models this is wired in. The other end is normally bare, so it can be more easily threaded though the car’s trim and bodywork. A couple of kits have a rounded protective nipple on the cable end, this helps enormously in confined spaces. You will have to obtain the correct plug for your phone or car-kit, and fit it yourself, get one at the same time as you buy the aerial. They’re not difficult to fit but it may involve soldering or the use of a crimping tool. When the cable has been installed it’s good practice to cut it to the correct length, and not coil any excess.  

 

That brings us to this month’s survey. A quick reminder that as usual we haven’t quoted typical retail prices, there’s no such thing in the cellphone accessory business! 

 

BOX COPY 1

THE TESTS

It’s important to say right from the beginning this is not an in-depth laboratory test. Whilst that would produce a wealth of authoritative data it would have little meaning to the average cellphone user, and even less bearing on what happens in the real world, where actual performance can be adversely affected by a multitude of factors, unrelated to the design of the antenna. We’ve developed a set of simple and we hope accessible testing procedures, that reflect typical conditions. Above all they are consistent, so that we can compare the results in a reasonably meaningful way. Our final performance ratings are necessarily quite general. Nevertheless these simple tests will expose any major deficiencies, and can show up quite subtle differences in performance.

 

In the first part of the test we use a static test rig. The antenna is connected to a cellphone with a highly sensitive digital signal strength meter and cell site channel identification display; this gives us a set of benchmark figures. The second part of the test is the ‘practical’ and this involves fitting each antenna to a vehicle, (the mounting point is the same for each antenna). It follows a pre-set route, including an area of known poor reception. Signal strength readings are taken at a series of fixed points, checking to ensure the same cell site is being accessed each time. Just to be sure we repeat each test at least once.

 

The last part of the test looks at the overall design of each antenna, with special emphasis on the quality of manufacture, corrosion protection, weatherproofing of the exterior components and how easy it is to remove the radiators, before going through a car wash, for example. We examine the contents of the fitting kits, how helpful the instructions are, and make careful note of how easy it is to install, (and subsequent removal, we’re getting quite good at that...).

 

ALLGON 1128 OB 3157

Part of Allgon’s ‘Glass Collection’ this is a tough, no-nonsense design. A very complete package containing the glass mount and detachable whip, coupler module, 5-metres of cable (terminated one end), cleaning swab, silicon adhesive, cable clips and two unwired plugs. The antenna mount attaches to the glass using a pad of double sided tape, and adhesive, so it’s very secure. The bulky coupler has tape only fixing. Adequate instructions, it’s easy to fit, and it works well.

 

Make/model                 ALLGON 1128 OB 3157

Type                            4dB colinear whip

Performance               ****

Ease of installation      ****

Instructions                 ***

Build quality                 ****

WC Rating                  85%

 

Contact                       ALLGON ANTENNAS, Unit 11, The Courtyard Whitwick Business Park, Stenson Road, Coalville, Leicester LE67 3JP. Telephone (01530) 510013

 

 

ALLGON CLIC B1138.1UK

‘Clic’ antennas feature simple slide-fitting removable radiator element. The package contains the whip, mounting plate with built in ground-plane, captive internal coupler with 5-metres of cable, cleaning swab and cable clips. Comprehensive instructions, includes useful tips and mounting template, to help alignment. Powerful double-sided tape, and light, slim profile couplers, very strong, and very difficult to remove. Simple removal facility a bonus, good performance.

 

Make/model                 Allgon CLIC B1138.1UK

Type                            3dB colinear whip

Performance               ****

Ease of installation      ****

Instructions                 ****

Build quality                 ****

WC Rating                  85%

 

Contact                       ALLGON ANTENNAS, Unit 11, The Courtyard Whitwick Business Park, Stenson Road, Coalville, Leicester LE67 3JP. Telephone (01530) 510013

 

 

CARANT GU 995

Unusually chunky design. Detachable whip features moulded wind ‘spoiler’ to reduce wind noise. Kit contains whip, mounting plate, interior coupler, cable clips, cleaning swab and allen key. Base module and coupler attach using strong double-sided tape. Reasonably helpful multi-lingual instructions, includes cut-out template to assist alignment. Average to good performance. 

 

Make/model                 Carant GU 995

Type                            3dB colinear whip

Performance               ***

Ease of installation      ****

Instructions                 ***

Build quality                 ****

WC Rating                  75%

 

Contact                       VEGA Bamford Village Centre, Martlett Avenue, Rochdale OL11 5QY. Tel: (01706) 44177

 

 

ORA CMS 895E

Simple, no-nonsense design supplied with 5 metres of non-terminated cable with captive coupler, glass cleaning alcohol swabs and drying cloth, silicon glass cement and sticky-backed cable-tidy clips. Instructions clear but at least one error, incorrectly showing position of trim ring. Detachable (screw-fitting) whip, good weatherproofing on the outside mount. Belt and braces glass mount with double-sided sticky pads and glass cement which dries in 30 mins (fully hardened in 24 hours), so it is very secure. Good performance, easy to install, not quite the best, but not far off.

 

Make/model                 Ora CMS 895E          

Type                            3dB colinear whip

Performance               ****

Ease of installation      ****

Instructions                 ***

Build quality                 ****

WC Rating                  85%

 

Contact                       ORA 28/29 Faraday Road, Aylesbury, Bucks HP19 3RY

Telephone (01296) 415445

 

 

ORA CMX 720E

A similar radiator to the CMS 895E but with a modified base mount and interior coupler, with ground plane ‘wings’ to improve efficiency. A very complete package with wet, dry and impregnated cleaning swabs, cable clips and silicon adhesive for a strong, weatherproof fixing. Clear, easy to follow instructions. Very slight improvement in receive signal strength, compared with 895.

 

Make/model                 Ora CMX 720E

Type                            3dB colinear with ground-plane

Performance               ****

Ease of installation      ****

Instructions                 ****

Build quality                 ****

WC Rating                  85%

 

Contact                       ORA 28/29 Faraday Road, Aylesbury, Bucks HP19 3RY

Telephone (01296) 415445

 

 

ONLINE AGC3DB

Standard design with chunky-looking square-sided plastic mount plate.  Package includes external antenna, coupler box, 5-metres of cable (non-terminated), impregnated cleaning swab and allen key. Screw-fitting detachable whip. Usual double-sided tape fixing, comparatively small area contacts glass on external antenna base as middle slightly indented. Inside coupler rather bulky. Instructions fairly brief and no illustrations. Average performance.

 

Make/model                 Online AGC3DB

Type                            3dB colinear whip

Performance               ***

Ease of installation      ***

Instructions                 **

Build quality                 ****

WC Rating                  75%

 

Contact                       ONLINE ACCESSORIES, 1-15 Kingston Road. Freemantle,

Southampton SO15 3DB. Telephone (01703) 237111

 

 

VIVANCO AGC 1040

Somewhat over-complicated design. Whip held captive by allen grub-screw on knurled base screw; difficult to tighten on our sample. Exterior base unit has exposed ground-plane elements, also act like magnets for naughty little boys, could be vandal-prone. Elaborate two-stage whip-angle adjustment/locking mechanism. Interior coupler has unusual BNC socket, supplied 4-metre cable on short side, and terminated with plugs at both ends, so it can be difficult to pass through tight openings. No instructions, two cleaning swaps supplied, fixing pads provide a fairly good grip. Average performance.

 

Make/model                 Vivanco AGC 1040

Type                            4dB colinear whip with ground-plane

Performance               ***

Ease of installation      ***

Instructions                 n/a

Build quality                 ***

WC Rating                  75%

 

Contact                       VIVANCO, Unit C, ATA House, Boundary  Way, Hemel Hempstead HP2 7SS. Telephone (01442) 231616

 

 

WALLEN PA008

This is the odd one out. The unique (pat-pending) ‘Dipacitor’ design has two 120mm (1/2 wave) elements, spaced at 80mm. This configuration is equally sensitive to horizontally and vertically polarised signals. The package contains the radiator module with removable whips, interior coupler with 5.5 metres of cable (unterminated). The double sided tape fixing is adequate, though the exterior module stands a millimetres or so proud of the glass and may be susceptible to water-ingress, some additional sealing compound around the edge might be a good idea. Good performance.

 

Make/model                 Wallen PA008

Type                            Dipacitor twin whip

Performance               ****

Ease of installation      ****

Instructions                 ***

Build quality                 ****

WC Rating                  85%

 

Contact                       WALLEN ANTENNAS, Les Wallen Manufacturing Ltd., Unit 1, Trinity Place, Ramsgate, Kent CT11 7HJ. Telephone (01843) 582864

 

 

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Ó R. Maybury 1995 1509

 

 


 

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