Browse Prior Art Database

A WELL BEHAVED HARDWARE DATA OPERATED MUTE (DATA OPERATED SQUELCH)

IP.com Disclosure Number: IPCOM000007539D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2002-Apr-04
Document File: 1 page(s) / 56K

Publishing Venue

Motorola

Related People

Douglas Wayne Eaton: AUTHOR [+2]

Abstract

Many communications systems use the same wire line or communications link for both data and voice. It is usually annoying and unnecessary for the users ofthe system to hear the data. As data and voice are never present at the same time, a data operated squelch (DOS) can mute the audio path during data. Unfortunately, the DOS data detector can be falsed by the voice information. Using audio filtering ahead of a data detector will not protect it from falsing as voice contains the frequencies used by the data detector.

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MoloRoLA Technical Developments

A WELL BEHAVED HARDWARE DATA OPERATED MUTE (DATA OPERATED SQUELCH)

by Douglas Wayne Eaton and Robert Edwin Swoger

1. THE PROBLEM 2. THE SOLUTION

  Many communications systems use the same wire line or communications link for both data and voice. It is usually annoying and unnecessary for the users ofthe system to hear the data. As data and voice are never present at the same time, a data operated squelch (DOS) can mute the audio path during data. Unfortunately, the DOS data detector can be falsed by the voice information. Using audio filtering ahead of a data detector will not protect it from falsing as voice contains the frequencies used by the data detector.

  Since the FSK demodulator used to detect the data is being falsed by voice, it is reasonable to assume that two identical demodulators will false in a simi- lar manner. Therefore, a second FSK demodulator is used as a voice detector to protect the DOS cir- cuit from voice falsing.

  The center frequency of the voice detector is tuned to a frequency just below the lower data frequency (LF) producing a Voice "1" at frequencies below this limit. The bandwidth of the voice detector is adjusted to maintain carrier detect (CD) just beyond the higher data frequency (HF) shown in Figure 1.

LF HF

Fig. 1

The carrier detect output of the data detector input gate shown in Figure 2. The gate votes whether and both outputs ofthe voice detector drive the three the signal is data or voice.

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