What is Cablefree?
are free-space optical
communication systems, offering atmospheric line-of-sight
transmission of high-speed digital signals over distances up
to and exceeding 1000m. State-of-the art infrared technology
offers major performance advantages over traditional cable or
radio systems, with huge available bandwidths in excess of
1.5Gbps. Unlike radio and microwave technologies, infrared
offers complete freedom from interference or radio licensing
does weather have?
Atmospheric weather effects such as fog,
snow, mist, rain, smog, thermal shimmer and sand storms all
act to attenuate or disturb the passage of light though the
systems are designed with a
‘fade margin’ which ensures operation during the normal
fluctuations in weather. Extremes of fog or thermal shimmer
are investigated during a site-survey to ensure excellent
reliability performance is achieved. The availability figure
links is typically between
99.997% and 99.7% depending on distance and location.
if the beam is broken?
normally installed away from ground level to avoid
beam-breakage from terrestrial objects such as people or cars.
Free-space systems are then of high integrity, with rare
events such as birds flying through the beam which disrupts
both optical and microwave systems – typically the data path
is broken for a small fraction of a second. As the optical
beams are relatively narrow, this phenomenon is statistically
extremely rare. In a data networking application, network
protocols such as Ethernet and Token ring merely re-send lost
packets and the result is transparent to the user. E1/G703
systems will experience ‘clicks’ in the audio traffic. CCTV
and Broadcast television will experience lost frames, which
may not even be perceptible if frame-stores are used elsewhere
in the system.
What are the
effects of sunlight?
Sunlight does not affect
systems in normal operation – a
combination of narrow viewfield, optical filtering to remove
out-of-band light and DC offset removal in the receiver ensure
that links remain working day and night. In very rare cases, a
poorly specified East/West installation could result in the
sun rising or setting behind one end of the link, temporarily
blinding the remote receiver. Although this condition causes
the link to be inoperative for several minutes while the sun
passes, no damage occurs and recovery is automatic. This
phenomenon affects not only optical systems but other
free-space links such as microwave.
What level of
maintenance is required?
extremely reliable in use, and are designed for continuous
24-hour all-year-round operation. Periodic maintenance is
minimal but advisable to check integrity of outdoor cables,
received signal levels and wipe any dirt or deposits from the
front face of the unit. None of these activities requires the
system to be disconnected or powered down. Installers and
users should be aware that trees or foliage in the
line-of-sight path may require periodic trimming.
Can I upgrade
a Cablefree system?
One of the main features of
Cablefree system is
the ability to perform upgrades on-site. Cablefree systems are
configured with interchangeable plug-in modules which allow
the link to be upgraded to match the rest of a network – a
feature not available from competitive systems or leased-line
operators. Typically, a 10Mbps Ethernet network can be
upgraded to 100Mbps, single-channel 2Mbps E1/G703 to E2 or
multiple 2Mbps channels, a CCTV system from single to multiple
video channels, or a complete change of use effected. Often
this can be done without removing or realigning the link,
though a brief verification of link performance is always
Is this a
duplex link? Can I have multiple channels?
systems are full-duplex links– each unit
has an independent transmitter and receiver subsystem. In a
data networking or telecommunications application, data flows
in both directions across the link. In a CCTV Security or
Broadcast Television environment, data, audio or images can be
sent in the return direction from the normal video
Plug-in modules allow a
system to support multiple channels of
2Mbps E1/G703 for telecommunications. For CCTV or Broadcast
use, up to 4 channels of video with auxiliary sound and
telemetry channels can be carried over a single link. External
industry-standard multiplexers can of course be used to allow
diverse types of data traffic to pass over a single link such
as 2Mbps E1/G703 or 155Mbps ATM/STM rates.
Can I see the
beams? Is it safe to do so?
Transmitted light is visible only when
standing directly in line with the link – the beams are
typically quite narrow. The infrared wavelengths used by
systems are just visible to the human eye as red, and are
most clearly seen at night. All
systems are certified to be eye-safe to
IEC standards – but tampering or attempting to open the case
can give rise to dangerous emissions. These are precision
optical instruments, and all Class 3B laser systems should be
treated with respect. Viewing with the naked eye is perfectly
safe, but avoid staring into the front of the unit at short
range using magnifying instruments such as a telescope or
Can I send
the beams through windows?
Yes - infrared beams used by
travel well through glass, though some of the signal is
reflected. The maximum range of the link through glass is
therefore slightly less than the free-air value. This can be
of use in temporary or covert applications, or for listed
transmission using Cablefree secure?
an extremely secure method of transmitting information. The
optical beams used are relatively narrow and of low divergence
– they cannot be detected outside the footprint of the beam.
An attempt to intercept data transmission is likely to
partially or completely block the beam, which is detectable by
the operator and can be used to halt data transfer – and the
attempt is visibly obvious due to the requirement to be ‘in
the beam’. Infrared beams cannot be detected using RF meters
or spectrum analysers, and require an optical receiver tuned
to the appropriate wavelength to decode them. For certain data
formats, proprietary line coding techniques used make the data
still more secure.
Cablefree compare to Microwave systems?
links use optical frequencies, and
therefore can offer higher bandwidths than physically possible
with Microwave technology – the trade-off is that receivers
are correspondingly less sensitive which makes infrared suited
to shorter ranges around 1-2km. Optical systems can be
configured to use tighter beams which removes the possibility
of interference with adjacent links – and they don’t suffer
from signal reflections from nearby objects. Atmospheric
effects affect both optical and microwave systems – for
infrared, fog is a major source of attenuation, but not rain –
the reverse is true for microwave. Optical systems such as
do not require frequency allocation permits or licenses.
How do I find
out more about Cablefree?
would be delighted to answer your
questions on infrared technology and how our systems could
suit your application. In addition to the examples given
is suited to a huge and
growing range of applications, with some exciting future
systems can be supplied
configured for your application directly from our head office
in Surrey, U.K, or from a number of appointed resellers.
Contact us for quotation or shipment details.
For further information please