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Browse Prior Art Database

AUTOMATIC IF BANDWIDTH ADJUSTMENT

IP.com Disclosure Number: IPCOM000006114D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2001-Dec-05
Document File: 2 page(s) / 81K

Publishing Venue

Motorola

Related People

Dave Muri: AUTHOR

Abstract

Current communication systems assign RF channels in a variety of channel spacings. Each FM channel spacing has a maximum allowable deviation specification associated with it. For optimum receiver performance the IF bandwidth should be adjusted to match this maximum allowable deviation. The problem to be solved is the identification of an unknown RF channel bandwidth such that appropriate changes can be made to the receiver's IF filter. The difficulty in determining the channel bandwidth for an analog FM voice channel is that the amplitude of the voice may be random enough that a false indication of the peak deviation will be derived.

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MOTOROLA INC. Technical Developments Volume 12 April 1991

AUTOMATIC IF BANDWIDTH ADJUSTMENT

by Dave Muri

  Current communication systems assign RF channels in a variety of channel spacings. Each FM channel spacing has a maximum allowable deviation specification associated with it. For optimum receiver performance the IF bandwidth should be adjusted to match this maximum allowable deviation. The problem to be solved is the identification of an unknown RF channel bandwidth such that appropriate changes can be made to the receiver's IF filter. The difficulty in determining the channel bandwidth for an analog FM voice channel is that the amplitude of the voice may be random enough that a false indication of the peak deviation will be derived.

  It is possible to identify the channel bandwidth by transmitting this additional information before, during, or after the voice/data transmission. Such additional information, however, is obtrusive and not universally accepted. An approach is needed that does not require a change to existing communication infrastructures.

  In many communications systems a CTCSS tone is transmitted simultaneously with voice or data. The method described herein uses the amplitude of the CKSS, or DPL information to predict the appropriate channel bandwidth for analog systems. The amplitude of the peak deviation is then used to effect changes to the IF filter.

  In the case where the CTCSS code (tone) is known, a narrow bandpass filter may be used to isolate the tone (see figure 1). A peak detector may be used to measure the amplitude of the tone thus determining the peak...