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Browse Prior Art Database

REMOTE ANTENNA FAULT DETECTION SYSTEM

IP.com Disclosure Number: IPCOM000008051D
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2002-May-15
Document File: 3 page(s) / 125K

Publishing Venue

Motorola

Related People

Edward Picha: AUTHOR

Abstract

In two-way radio systems, the base station antenna and transmission line are typically the sys- tem components requiring a high degree of on- going maintenance. They are exposed to the ele- ments, and over time they show the effects of repet- itive lightening strikes.

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Page 1 of 3

MOTOROLA Technical Developments

REMOTE ANTENNA FAULT DETECTION SYSTEM

by Edward Picha

INTRODUCTION

  In two-way radio systems, the base station antenna and transmission line are typically the sys- tem components requiring a high degree of on- going maintenance. They are exposed to the ele- ments, and over time they show the effects of repet- itive lightening strikes.

  In addition to deterioration due to the elements, antenna system performance can degrade due to man-made causes as well. At today's increasingly dense RF sites, new systems are often installed with little regard for the performance of existing antenna systems, Specifically, changes in radiation pattern characteristics can occur due to conductive objects (new antennas) installed near an existing antenna system.

  Technicians responsible for system performance need a way to find out about degradation in system performance. Typically they rely on the method of users reporting they can't communicate where they used to be able to communicate. This method is

unreliable at best.

  Current commercially available antenna fault monitoring systems generally consist of some method of monitoring forward and reflected power at the transmitter frequency, and somehow signaling a fault when the VSWR exceeds a set threshold. While this scheme can detect gross antenna or transmission line faults, it will not detect more sub- tle changes in the system. This scheme also requires a transmitter for operation.

A DIFFERENT APPROACH

  Rather than monitor the performance of the antenna system at one specific frequency, the per- formance over the full specified range of operation can be monitored. Antenna performance is typically specified by a particular frequency bandwidth where the VSWR will not exceed a threshold (typi- cally 2: 1). Refer to figure 1, and consider a hypo- thetical system with a base transmit frequency of 470 MHz, and receive frequency of 469 MHz.

466 469 470 471 472 473

Frequency (MHz)

Fig. 1

0 Mafc'rola, 1°C. 1997 139 March 1997

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m MOTOROLA Technical Developments

  Now consider what could happen to this nomi- na otherwise experiences some kind of physical nal VSWR vs. frequency curve when a conductive change. Refer to figure 2.
device is installed close to the antenna, or the anten-

1.51

Conventional fault monitoring system VSWR threshold at 1.5: 1

Note that VSWR at system receive fre- quency has exceeded the conventional alarm monitor threshold, but goes unde- tected!

VSWR

468 469 470...