mobile | classic
Dataweek Electronics & Communications Technology Magazine





Follow us on:
Follow us on Facebook Share via Twitter Share via LinkedIn


Search...

Electronics Buyers' Guide

Electronics Manufacturing & Production Handbook 2019


 

Introduction to coaxial cable losses
15 August 2018, Interconnection

Coaxial cable transfers radio frequency power from one point to another and, in the ideal world, the same amount of power would transfer along the cable to the remote end of the coax cable. However, real world conditions include some power loss along the length of the cable. Loss, or attenuation, is one of the most important features to look for when deciding what type of coaxial cable to use in a design.

Loss is defined by decibels per unit length and at a given frequency. Thus, the longer the coaxial cable, the greater the loss. Loss is also frequency dependent, generally increasing with frequency, but the loss is not necessarily linearly dependent upon the frequency. Power loss occurs in a variety of ways.

Resistive loss

Resistive losses within the coaxial cable occur when the resistance of the conductors and the current flowing in the conductors results in heat being dissipated. Skin effect limits the area through which the current flows, which leads to increased resistive losses as the frequency rises.

To reduce the level of resistive loss, the conductive area is increased, resulting in larger low-loss cables. Also, multi-stranded conductors are often used. Resistive losses generally increase as the square root of frequency.

Dielectric loss

Dielectric loss is signal energy dissipated as heat within the insulating dielectric of a cable, but is independent of the size of the coaxial cable. Dielectric losses increase linearly with frequency, and the resistive losses normally dominate at lower frequencies. As resistive losses increase as the square root of frequency and dielectric losses increase linearly, the dielectric losses dominate at higher frequencies.

Radiated loss

Radiated loss in a coaxial cable is usually much less than resistive or dielectric losses, however a poorly constructed outer braid on some coaxial cables may yield a relatively high radiated loss.

Radiated power, problematic in terms of interference, occurs when signal energy passing through the transmission line is radiated outside of the cable. Leakage from a cable carrying a feed from a high-power transmitter may produce interference in sensitive receivers located close to the coax cable or a cable being used for receiving can pick up interference if it passes through an electrically noisy environment.

To reduce radiated loss or interference, double- or triple-screened coaxial cables are designed to reduce the levels of leakage to very low levels.

Of these forms of loss, radiated loss is generally the less concerning as only a very small amount of power is generally radiated from the cable. Thus, most of the focus on reducing loss is placed onto the conductive and dielectric losses, except in certain applications.

Loss over time

Loss or attenuation of coaxial cables tends to increases over time as a result of flexing and moisture in the cable. Although some coax cables are flexible, the level of loss or attenuation will increase if the RF cable is bent sharply or if there is a disruption to the braid or screen.

Contamination of the braid by the plasticisers in the outer sheath or moisture penetration can affect both the braid where it causes corrosion and the dielectric where the moisture will tend to absorb power. Often, coax cables that use either bare copper braid or tinned copper braid experience more degradation than those with the more expensive silver plated braids.

Although foam polyethylene provides a lower level of loss or attenuation when new, it absorbs moisture more readily than the solid dielectric types. Cables with solid dielectric polyethylene are more suited to environments where the level of loss needs to remain constant or where moisture may be encountered. Even though RF coaxial cables are enclosed in a plastic sheath, many of the plastics used allow some moisture to enter; thus, for applications where moisture may be encountered, specialised cables should be used to avoid performance degradation.

For more information contact Andrew Hutton, RF Design, +27 21 555 8400, andrew@rfdesign.co.za, www.rfdesign.co.za


Credit(s)
Supplied By: RF Design
Tel: +27 21 555 8400
Fax: 086 653 2139
Email: sales@rfdesign.co.za
www: www.rfdesign.co.za
  Share on Facebook Share via Twitter Share via LinkedIn    

Further reading:

  • Waveguide antennas for millimetre-wave
    29 May 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    Pasternack has released a new line of waveguide antennas designed to address R&D, military/aerospace, experimental radar, test and measurement, and wireless communication applications from 40 GHz to 220 ...
  • GNSS module for lane-accurate positioning
    29 May 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    New from u-blox comes the ZED F9K high-precision multiband GNSS (global navigation satellite system) module with built-in inertial sensors. The module combines the latest generation of GNSS receiver technology, ...
  • High-speed M12 connectors for transportation
    29 May 2019, Webb Industries, Interconnection
    Telegärtner’s range of connectors for railway and vehicle applications has been expanded with the introduction of a new product series. An add-on to the previous M12 connector series, the new series contains ...
  • Board-to-board connectors
    29 May 2019, TRX Electronics, Interconnection
    A new product series of robust board-to-board connectors from Phoenix Contact includes shielded connectors with a pitch of 0,8 mm and unshielded versions with a pitch of 1,27 mm. The Fine Pitch series ...
  • 50 GHz mixers in SMT packages
    29 May 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    Marki Microwave has introduced its first 50 GHz surface-mount products, the MM1-1850HSM and MM1-1850SSM double-balanced mixers. These GaAs MMIC mixers offer wide bandwidths and high linearity in a proprietary ...
  • Wall-mount iDAS antenna
    29 May 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    The iDAS.W.001 from Taoglas is a MIMO LTE wall-mount panel antenna designed for use in indoor distributed antenna systems (iDAS) to address in-building coverage issues in office buildings, stadiums, conference ...
  • Durable board-to-board connector
    29 May 2019, Otto Marketing, Interconnection
    Hirose Electric has developed a high contact reliability connector with a -40°C to 140°C operating temperature that maintains high performance in vibration environments, including on-board powertrain. While ...
  • Broadband low-noise amplifier
    29 May 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    Custom MMIC’s CMD283 is a broadband MMIC low-noise amplifier (LNA) that operates from 2 to 6 GHz (S and C bands). The device delivers 27 dB of gain with a corresponding noise figure of 0,6 dB at 4 GHz ...
  • Coax-to-PCB connectors
    29 May 2019, TRX Electronics, Interconnection
    Amphenol SV Microwave’s high-speed RF/coaxial solderless edge launch connectors are ideal for high-frequency printed circuit board applications where precision is key. These rugged and durable interconnects ...
  • SPDT RF switch
    29 May 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    The InP1012 from Teledyne is a monolithic, reflective SPDT (single-pole double-throw) active RF switch that operates from DC to 60 GHz. It has an insertion loss of 3,7 dB, a return loss of 26 dB and provides ...
  • Is the supply chain broken?
    30 April 2019, Electrocomp, Diel Met Systems, ExecuKit, NuVision Electronics, RF Design, This Week's Editor's Pick, News
    The world’s insatiable demand for electronic goods has created a monster: a supply chain that spans the globe and relies on the entirety of our collective knowledge and experience in the pursuit of industry.
  • Choosing the right connector for harsh environments
    30 April 2019, TRX Electronics, This Week's Editor's Pick, Interconnection
    While connectors are sometimes left to last in a system design, they are essential components, and you need to get their selection right.

 
 
         
Contact:
Technews Publishing (Pty) Ltd
1st Floor, Stabilitas House
265 Kent Ave, Randburg, 2194
South Africa
Publications by Technews
Dataweek Electronics & Communications Technology
Electronics Buyers’ Guide (EBG)

Hi-Tech Security Solutions
Hi-Tech Security Business Directory

Motion Control in Southern Africa
Motion Control Buyers’ Guide (MCBG)

South African Instrumentation & Control
South African Instrumentation & Control Buyers’ Guide (IBG)
Other
Terms & conditions of use, including privacy policy
PAIA Manual





 

         
    Classic | Mobile

Copyright © Technews Publishing (Pty) Ltd. All rights reserved.