Datasheet

The most common way to make announcements over a paging system is through the telephone system. It is a convenient
and readily available live input source. However, audio and telephone technologies are different. This sometimes makes
it necessary to use an adapter to link the two systems together.
There are many types of telephone ports possible in telephone switches. The four types presented here – Page Port, Loop
Start trunk, Ground Start trunk, and Analog ring-up station – are the only ones Bogen recommends as interfaces to
telephone systems. Other port types and specifically digital station ports are not suitable for connection to amplifiers and
interface devices.
• The Loop Start, or CO port, is the most popular type of paging interface
to use when a page port is not available or suitable
• A Ground Start trunk uses loop current but employs a request and
acknowledgment handshake for making the initial connection
• An interface device is necessary when connecting a trunk to an amplifier
• When paging, an interface adapter detects the off-hook condition of
the trunk and connects the amplifier to the trunk port through
signal conditioning electronics
• When the trunk is released, the adapter detects the on-hook condition
and immediately disconnects the amplifier from the trunk
• A pop at the end of a page is typically present due to the large change
in telephone line voltage between on- and off-hook conditions
• An analog station allows interfacing when neither a paging port nor
a trunk port is available
• Analog ring-up interfacing requires a more sophisticated interface
than other methods
• The interface must detect a high-voltage ring signal and answer the call
to start the page
• To determine when to disconnect the page, typically two system timers are
used — one limits the maximum length of the page to ensure disconnection,
the other senses audio activity and disconnects after a preset length
of silence
• Many telephone switches now provide a calling party control (CPC) signal,
which indicates to the interface that the caller has disconnected;
Bogen interfaces disconnect immediately upon detecting a CPC signal
• Dedicated audio output available standard on most telephone systems
• Can be connected directly to the input of most amplifiers
• Traditionally a 600-ohm dry audio signal and a normally open
control contact closure
• Control contacts, if available, activate during a page and typically
control the muting of background music
• Some page ports provide only an audio pair, which requires that audio
equipment have voice-activated (VOX) functions such as background
music muting
• Paging ports are not always bi-directional like telephone lines
(bi-directionality is necessary when including talk back capability in
a paging system)
• Not all paging ports will produce DTMF tones which are necessary
when using zone paging equipment
Page Ports
Loop And Ground Start
Analog Station
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SYSTEM DESIGN GUIDE
TELEPHONE INTERFACES