Browse Prior Art Database

INTERMODULATION PROTECTION FOR RADIO SYSTEM

IP.com Disclosure Number: IPCOM000006686D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2002-Jan-23
Document File: 2 page(s) / 83K

Publishing Venue

Motorola

Related People

Stephen P. Flood: AUTHOR

Abstract

It is becoming essential to develop methods to com- bine multiple base repeaters onto a single antenna. Power monitoring is a necessary component of the antenna combining equipment. To eliminate the interference to the base receivers, protection against Intermodulation Distortion (IMD) is necessary.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

Page 1 of 2

MOZY)ROLA INC. Technical Developments Volume 17 December 1992

INTERMODULATION PROTECTION FOR RADIO SYSTEM

by Stephen I? Flood

   It is becoming essential to develop methods to com- bine multiple base repeaters onto a single antenna. Power monitoring is a necessary component of the antenna combining equipment. To eliminate the interference to the base receivers, protection against Intermodulation Distortion (IMD) is necessary.

  An antenna combing system is shown in Figure 1. Multiple transmitters are duplexed onto a single antenna with multiple receivers. A power monitor is used at the antenna port to monitor forward power from the trans- mitter and reflected power from the antenna. For accu- rate monitoring of the transmitter performance, both a forward power and a reflected power monitor are used at the antenna port. This provides detection of the antenna and combining equipment degradation or failure. Plac- ing the power monitor before the duplexer would impair the ability to accurately monitor antenna and duplexer degradation. Duplexer VSWR and insertion loss can mask detection of partial antenna failure resulting from wind damage or antenna icing.

  In the 800 MHz trunking band the receive and tramsmit frequencies for a base repeater are offset by 45 MHz. Two transmitters separated by 11.25 MHz or 15 MHz can create a 7th order Intermodulation Distor- tion product that falls on the receive frequency. The 7th order IMD products are illustrated in Figure 2. To pre-

vent interference to the receiver the IMD product would have to be C-120 dBm. This requires a IMD product spec of -170 dBc for 100 watt transmitter powers. Higher order intermodulation products can also create interfu- ence...