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SIGNALLING BLANKING FOR ANALOG RADIOS USING IN-BAND SIGNALLING

IP.com Disclosure Number: IPCOM000008103D
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2002-May-17
Document File: 1 page(s) / 45K

Publishing Venue

Motorola

Related People

Wolfgang Schier: AUTHOR

Abstract

Some analog trunked radio communications systems that use in-band signalling techniques to transmit signalling information, e.g. MPT1327 with frequency shift keying, within the audio (speech) bandwidth via signalling tones. This signalling information is occasionally, and undesirably, audi- ble in the radio loudspeaker as noise. In MPT1327 radio units these signalling tones are generated every time the radio user presses or releases the PTT, either during call cancellation or for status request purposes.

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MOTOROLA Technical Developments

SIGNALLING BLANKING FOR ANALOG RADIOS USING IN-BAND SIGNALLING

by Wolfgang Schier

INTRODUCTION

  Some analog trunked radio communications systems that use in-band signalling techniques to transmit signalling information, e.g. MPT1327 with frequency shift keying, within the audio (speech) bandwidth via signalling tones. This signalling information is occasionally, and undesirably, audi- ble in the radio loudspeaker as noise. In MPT1327 radio units these signalling tones are generated every time the radio user presses or releases the PTT, either during call cancellation or for status request purposes.

IMPLEMENTATION

  It is proposed that in order to avoid this audible "noise" a combination of signalling-decoder and voice storing process be used. The preferred approach is:

  1. The voice store in the radio unit delays the received audio information by the length of the sig- nalling telegram, e.g., in MPT1327 this is approx. 100ms.

2. The received audio information is put in the voice store and monitored by the signalling decoder.

  3. As soon as the signalling decoder detects the signalling information in the audio signal, the sig- nalling information will be removed from the voice store and not passed to the loudspeaker.

  Hence, the speech information only, and not the signalling tones, are subsequently heard in the loud- speaker.

e3 Motomla, hc. L997 165 March 1997

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