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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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