A Guide to Coaxial Tecnology

A Guide to
Coaxial Technology
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Coaxial Cable
Coaxial or Coax cable is a type of electrical cable that has an inner
conductor surrounded by a tubular insulating layer, surrounded by a
tubular conducting shield all within a plastic outer sheath. This is
called a coaxial cable as the inner conductor and the outer shield are
concentric.
PVC Jacket
Braided Shield
Dielectric
Typical Example of
Flexible Coaxial Cable
Centre Core
Coaxial cable is a type of transmission line. A transmission line is a
specialised structure designed to conduct alternating current of
radio frequency. Current at this frequency has a wave
characteristic. Transmission lines are used for connecting radio
transmitters and receivers with their antenna, distributing cable
television signals, trunk lines routing calls between switching
centres, computer network connections and high-speed data
buses. In general, coaxial cables and connectors are used in
broadcast of television signals and machinery that has a video feed,
for example machine vision for production lines or medical
imagery.
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RF connectors
A coaxial RF connector (Radio Frequency Connector) is an electrical
connector designed to work at radio frequencies in the multi
megahertz through gigahertz range.
RF connectors are typically used with coaxial cables and should be
designed to match the electrical characteristics of the cable whilst
providing a means of connection.
RF connectors are also available in PCB mounting version which
provide the connection from the source equipment or receiver
equipment.
Coupling Nut
Outer Conductor
Ferrule
Centre Pin
Insulator
All coaxial connectors have three main parts to them:
Outer Conductor– to provide an electrical path for the cable shield
through the connector couple.
Centre Pin – to provide and electrical path for the cable centre
conductor through the connector couple.
Insulator – to provide and electrical isolation between the outer and
centre conductor.
A coaxial cable connector will also have:
The means to electrically and mechanically connect the coaxial
cable. This function of the connector is specific to each cables
mechanical and electrical specifications.
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RF Connector Types
BNC (Bayonet Neill-Concelman)
The BNC is a quick disconnect radio
frequency connector used with
coaxial cable. It features two
bayonet lugs on the female
connector and a quarter turn
coupling nut on the male
connector. The majority of board
mounted connectors are female
while cable mounted connectors
tend to be male.
Micro BNC
The Micro BNC has the same
characteristics of the BNC
connector in a miniaturised form,
which allows significantly higher
densities when designing PCB
board layouts. The Micro BNC is
also known as a they HD-BNC TM or
Ultra Tiny BNC.
DIN 1.0/2.3
The DIN 1.0/2.3 was introduced in
the 1990’s initially for
telecommunication application.
They feature a push/pull lock and
release feature and are suited to
applications where space it limited.
BNC PCB
Mounted
Micro BNC
PCB
Mounted
DIN 1.0/2.3
PCB
Mounted
BNC Cable
Mounted
Micro BNC
Cable
Mounted
DIN1.0/2.3
Cable
Mounted
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How Does Broadcasting Work ?
Digital data containing all the information necessary to define a video
transmission is sent from a transmitter to a receiver through a
transmission media such as air, copper or fibre. The transmitters
typically form part of the broadcast infrastructure and the receiver is
typically located in the home as a TV or set top box.
Television creates the moving
pictures by repeatedly sending still
pictures called frames, so quickly
that your eyes view them as a
moving image, as opposed to
separate pictures. This is a more
technically advanced and faster
moving version of a flick book
animation.
In a television, the frame rate is the number of times in a second that
the pictures are refreshed. Most standard televisions refresh the
screen at 60 frames per second (60Hz), but 4K televisions may have a
120 or 240 frames per second (120Hz/240Hz) refresh rate. This means
that the picture that is shown appears smoother due to the speed of
the frames changing.
All frames (pictures) are composed of pixels (picture element). The
higher the number of pixels in each frame the clearer the final picture
will be and images are more defined, hence why this is called the
screen definition or resolution. The most common resolutions used
now are:
720p - @900 pixels -HD Ready
1080p - @2005 pixels – Full HD
4K - @4000 pixels – 4K UHD TV
8K - @8000 pixels – 8K UHD TV
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Serial Digital Interface
Serial Digital Interface (SDI) is a professional digital video interface
standard that has been used since the early 90s. The SDI is a family of
digital video interfaces that was first standardized in 1989 by SMPTE
(The Society of Motion Picture and Television Engineers). Additional
versions of the SDI standard have been developed to support
continuously increased resolutions (HD, UHD, 4K, 8K), higher bitrates
and more colors.
CEI offers connectivity products to fully support the following
standards:
The 3G-SDI standard is a 3 Gbit/s
interface which was standardised in 2006
and supported the 1080p full HD over a
single channel at a frame rate of 60Hz
(fps), following the SMPTE standard
424M.
The 6G-SDI standard is a 6 Gbit/s
interface, which was announced in 2015,
supports the 4K resolution over a single
channel at a frame rate of 30Hz (fps) or
60Hz (fps) over a dual channel, following
the SMPTE standard ST-2081.
The 12G-SDI standard is a 12 Gbit/s
interface which was introduced in 2015
and updated in 2018, supports the 4K
resolution over a single channel at 60Hz
or 8K resolution over a single channel at
30Hz, following the SMPTE standard ST-
2082.
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CoaXVision
CoaXVision is the CEI trading name for any connector falling under
the CoaXPress standards, which started in 2010.
Used mainly in the machine vision sector, CoaXPress is a digital
interface standard developed for high speed image data
transmission. The standard provides for a number of bit rates and
subsequent transmission distances, as defined in the table below.
The connectors supported by this standard are BNC, DIN 1.0/2.3 and
micro BNC, all with a 75 ohm impedance. The standard is a scalable
standard and can be used for connections from 1.25 Gbit/s up to
12.5 Gbit/s in a single link.
Standard Name Bit Rate (Gbit/s) Maximum Distance (m)
Belden 1694A
CXP-1 1.25 130
CXP-2 2.5 110
CXP-3 3.125 100
CXP-5 5 60
CXP-6 6.25 40
CXP-10 10 40
CXP-12 12.5 30
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Impedance
There are mainly two impedances used in RF transmission systems. 50
ohm, for higher power signals, such as transmission base stations and
75 ohm for low power signals. 75 ohm offers a lower signal loss than
50 ohm.
It is important to transfer radio frequency energy from a source to a
receiver through the transmission lines with minimum power loss. An
impedance mismatch in a transmission line will cause some of the
signal power reaching the receiver to be reflected back on itself
causing a return loss.
You should never mix 50ohm and 75ohm cables and connectors in the
same system. To achieve optimum results it is best practice to use
cables and connectors of the same impedance.
What is the difference between a 50 ohm and 75 ohm connector ?
The internal materials and structure.
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Materials
Connector Body
Zinc : Zinc bodies are normally die cast
and plated with nickel or gold to give a
wear and corrosion resistance and
make solderable to a PCB.
Brass : Brass bodies are normally
machined and can be plated with
nickel, tin or gold to give resistance to
wear and corrosion and also aid with
soldering to a PCB.
Zinc / Nickel
Plated
Brass / Tin
Plated
Brass / Nickel
Plated
Brass / Gold
Plated
Centre Pin
Most centre pins are made from
a metal alloy for strength with a
gold plating to improve
conductivity.
The main metal alloys are:
Insulators
Insulators are chosen for their
mechanical, electrical and
thermal properties. PEEK is used
in nuclear applications as it has
radiation resistance properties.
Beryllium Copper
PTFE
Phosphor Bronze
UL94 HB TPX
Brass
PEEK
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Mounting Types
PCB mountings
Right Angle – A connector with through hole right
angled centre pin. The connector body will have legs
that go through the board.
Edge Mount – The centre pin of an edge mounted
connectors is straight and can be surface mount.
Posts go through the board at right angles to hold
the connector in place.
Surface Mounted - The centre pin is the surface
mounted part of this connector and the legs are right
angled through hole for mechanical stability.
Top Entry – A top entry connector has a straight pin
that goes through the board and the connectors is
perpendicular to the PCB.
All PCB mounted connectors mentioned above are
available with a number of leg or post lengths
suitable to different board thicknesses.
End Launch – The pin of an end launch connector is
straight and the PCB goes between the legs of the
connector. The distance between the legs on an end
launch connector can differ to suit different board
thicknesses.
Cable Mountings
Straight – With a straight pin that will be crimped or
soldered onto the cable.
Right Angled – The cable is crimped or soldered at
the right angle join with the straight pin.
Bulkhead Mounting
A connector that is fixed to a bulkhead either by a single jam nut or by
four screws and is hardwired on one side and has a mating free
connector on the other side.
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For more information on the full range of connectivity
products offered by Cambridge Electronic Industries, visit
our website at:
www.CambridgeElectronics.com
Cambridge Electronic Industries Ltd
Pembroke Avenue
Denny Industrial Centre
Waterbeach
Cambridge
Cambridgeshire
CB25 9QR
Tel No: +44 (0)1223 860041
Tel No: +44 (0)1223 863377
Fax No: +44 (0)1223 863625
E-mail: sales@cambridgeelectronics.com
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