Wheelock MX-8 Mixer Specifications download pdf (Page 21)

Centrex systems work very much like PBX systems with one important difference: Instead of being located on prem-

ise,theswitchinggearislocatedatthetelephonecompany’scentralofce(CO).Theextensionlinescomebackfrom

COliketelephonelinescomingintoyourhome—with90-130voltringingvoltage.Centrex lines cannot be directly

connected to amplier inputs. An telephone paging interface must be used to connect a ring voltage line to a paging

system.Thetelephonepaginginterfaceanswersaregularringingvoltageline(suchasCentrex,stationlevelPBXor

singlelineresidentialtypephoneservice)andthenopensanaudiopathforconnectiontoadditionalequipmentsuchas

aWheelockpagingsystem(MZC-144).

™—AT&Tregisteredtrademark

Using Unused CO Ports

Some EKSU’s and PBX’s have no built-in paging access. In such cases, an unused CO line port or trunk port can be

used. However, talk battery (“A” battery) must be provided in these applications.

What is it?

Talkbatteryor“A”batteryistheDCvoltagesuppliedbythetelephonecompany(CO)centralofceto:

  A) Operatethecarbontransmitterinthetelephonehandsetstoallowaudio  

 (talking).

  B) Enableinitiationofcalls.

  C) AllowcommunicationthroughtheCOtrunkportsofatelephonesystem  

 (PBX,key,hybrid)installedinacustomer’spremise.

Talkbattery(usually48VDC)isconstantlypresentontheTIP(green)andRING(red)wiresofeachtelephonecom-

pany line. Note that talk battery is not to be confused with ring voltage, which is an AC voltage of about 105 volts

and is superimposed right on top of the 48 VDC talk battery, over the same pair of wires, for the purpose of ringing a

telephone.

How does it affect telephone paging applications?

When paging is connected to a telephone system’s unused CO trunk port, talk battery is not available at that port. The

operativewordis“unused”.ThatmeanstheCOportisnotconnectedtoapublictelephone(CO)line.Ifthetelephone

line is not connected to the port, then the talk battery the line would otherwise provide is simply not present. Neverthe-

less, the telephones within the system need to access that port for paging, so the port still needs talk battery for audio

(paging).Therefore,talkbatterymustbesuppliedbythepagingequipment.

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Wheelock MX-8 Mixer Specifications Page 21