Browse Prior Art Database

AUTOMATIC RECEIVER IM DETECTION AND PROTECTION SYSTEM

IP.com Disclosure Number: IPCOM000007331D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2002-Mar-15
Document File: 1 page(s) / 47K

Publishing Venue

Motorola

Related People

James Gehrke: AUTHOR [+2]

Abstract

It is common practice to switch the gain of a receiver to improve performance of a receiver when suffering interference from Inter modulation signals. The 'Local/Distance' switch is used on Motorola Radius products and may other receivers. The prob- lem with known products is that the switch is a manual operation controlled by the user. This is unde- sirable because it takes an experienced user to iden- tify IMing signals for analog systems from the detected audio. In addition this is not practicable in the new digital systems because the recovered voice coding degradation does not have a recognizable audio characteristic. So an automatic system to switch to lower receiver gain for the best performance is required.

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MOlYWilOLA Technical Developments Volume24 March 1995

AUTOMATIC RECEIVER IM DETECTION AND PROTECTION SYSTEM

by James Gehrke and Pete Walter

BACKGROUND:

PRINCIPLE OF OPERATION:

  It is common practice to switch the gain of a receiver to improve performance of a receiver when suffering interference from Inter modulation signals. The 'Local/Distance' switch is used on Motorola Radius products and may other receivers. The prob- lem with known products is that the switch is a manual operation controlled by the user. This is unde- sirable because it takes an experienced user to iden- tify IMing signals for analog systems from the detected audio. In addition this is not practicable in the new digital systems because the recovered voice coding degradation does not have a recognizable audio characteristic. So an automatic system to switch to lower receiver gain for the best performance is required.

  The basic approach is to use the ability of a receiver to detect peak deviation of a signal larger than allowed for the transmitter. This excess devia- tion is caused by the 3rd order or higher transfer characteristic that generates IM interference. Excess deviation detection is quite simple with DSP based receivers back IFS and detectors but a standard ana- log radio could measure the peak recovered audio before de emphasis. When this over-deviation is detected the system would lower receiver RF ampli- fier gain. This gain change will decrease on prob- lem IM products faster tha...