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:

  • Compression lugs and splices
    26 June 2019, TRX Electronics, Interconnection
    Panduit Pan-Lug compression connectors provide permanent terminations for a variety of power and grounding applications. The connectors are designed for use with many different code and flex conductor ...
  • Positioning module for autonomous driving
    26 June 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    The ZED-F9K from u-blox is a high-precision multiband GNSS (global navigation satellite system) module with built-in inertial sensors. The module combines the latest generation of GNSS receiver technology, ...
  • Test point pins
    26 June 2019, Vepac Electronics, Interconnection
    The range of terminal pins available from Vero Technologies provide an easily useable fitting on a through-hole printed circuit board (PCB) for the attachment of oscilloscope probes, multimeter leads ...
  • Pin strips for KNX applications
    26 June 2019, Wiltron Agencies, Interconnection
    The pins of the STL190 through-hole pin strips were designed by PTR specifically for KNX applications in home, building and system technology. Positioned by means of a carrier pad at a spacing clearance ...
  • Positioning and cellular antenna
    26 June 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    The Tycho MA310 antenna is a combination, small form factor GPS/GLONASS and penta-band cellular (GSM/GPRS/CDMA/ PCS/DCS/ WCDMA/UMTS) antenna to simplify AVL or fleet management antenna systems worldwide. Made ...
  • RF power doubler
    26 June 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    The QPA3357 from Qorvo is a power doubler that operates from 47 to 1218 MHz. It provides an output power of 57 dBm, a gain of 28 dB, and has a noise figure of 4,5 dB. This power doubler is matched to ...
  • Flexible wideband antenna
    26 June 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    The Taoglas FXUB64.18.0150C flexible wideband antenna has been designed to cover all working frequencies in the 600-3000 MHz spectrum, covering all cellular, 2,4 GHz Wi-Fi, ISM, NB-IoT, CAT-M1 and A-GPS ...
  • High-frequency power dividers
    26 June 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    Pasternack has launched a new series of high-frequency power dividers targeted at 5G cellular communication, automotive radar and satellite communication applications. The lineup consists of 17 new ...
  • High-temperature FFC/FPC connectors
    26 June 2019, Otto Marketing, Interconnection
    Hirose Electric’s new FH52K series of robust flat flexible cable/flat printed circuit (FFC/FPC) connectors are designed to withstand higher operating temperatures than standard FFC/FPC connectors. The ...
  • Cellular module for LPWA applications
    26 June 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    u-blox has announced the SARA R5 series of LTE M and NB-IoT modules for low power wide area (LPWA) IoT applications. The module, built on the UBX R5 cellular chipset and the M8 GNSS receiver chip, is ...
  • Hinged 4G LTE antenna
    26 June 2019, RF Design, Telecoms, Datacoms, Wireless, IoT
    The hinged Apex II TG.35 wideband dipole antenna from Taoglas has been designed to cover all cellular, ISM and Wi-Fi working frequencies in the 600-6000 MHz spectrum. It has been primarily designed for ...
  • Modular fibre-optic patch panel
    26 June 2019, Webb Industries, Interconnection
    The latest from Webb Industries is Telegärtner’s Fibre Termination Box (FTB) – a modular fibre-optic patch panel system which facilitates customised cabling in locations where large numbers of apartments ...

 
 
         
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.