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Browse Prior Art Database

PL TRANSMISSION IN SIMULCAST SYSTEMS

IP.com Disclosure Number: IPCOM000008336D
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2002-Jun-06
Document File: 2 page(s) / 94K

Publishing Venue

Motorola

Related People

Seiler Reinhard: AUTHOR

Abstract

This paper describes a method for Private Line (PL), otherwise known as continuous Tone Carrier Squelch System (CTCSS) tone transmission in simulcast RF communication networks, that offers advantages over existing transmissions in that tones are transmitted over normal voice grade leased land lines with an audio frequency range of 300-3400 Hz.

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MOTOROLA Technical Developments

PL TRANSMISSION IN SIMULCAST SYSTEMS

by Seiler Reinhard

INTRODUCTION

  This paper describes a method for Private Line (PL), otherwise known as continuous Tone Carrier Squelch System (CTCSS) tone transmission in simulcast RF communication networks, that offers advantages over existing transmissions in that tones are transmitted over normal voice grade leased land lines with an audio frequency range of 300-3400 Hz.

PROBLEM TO BE SOLVED

  If a PL (or CTCSS) function is ,used in a simul- cast RF system, there is a requirement to transmit these sub-band frequencies for example 65-250 Hz tones coherently with respect to all other transmitters in the system. This prevents the use of independent tone encoders on the different transmit sites. On the other hand, if these transmitters are controlled by leased lines, the sub-band frequencies cannot

be transferred via these leased lines due to the bandpass characteristic employed in such land- based systems.

PROPOSED SOLUTION

  A tone of frequency F 1, near the lower edge of the leased line band (e.g. 290 Hz < FI < 325 Hz), is transmitted to a remote transmitter where it is used as a reference frequency for either a Phase Locked Loop (PLL), a divider, or in a Digital Signal Processor (DSP), which in turn creates the PL frequency to be used. Techniques by simple use of division e.g. 1.5 or 2, frequencies of 193-217 Hz or 145-163 Hz, respectively, can be generated.

  A preferred arrangement for providing the tone frequency Fl in leased line systems is shown in Figure 1.

j ___________________

_ _._________.____._________

_ __________:

0 Transmiflel

1

.ine BP 1 1 1 Notch \/ 1 Audio

Leased Line

Ref. 'VL F, Frequ. generator

' Band- $ pass

02

!--------06.-.......--------.----.---------~or:

DSp -2

Fig. I

0 Mowrds, 1°C. ,997 139 September 1997

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