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SP-1
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18
"The only practical and economical solution used to date is to design the
speakerphone to function in a half-duplex mode: only one person speaks at a
time while the other listens. To achieve this requires a circuit which can detect
who is talking, switch on the appropriate path (transmit or receive) and switch
off (attenuate) the other path. In this way, the loop gain is maintained less than
unity. When the talkers exchange function, the circuit must quickly detect this,
and switch the circuit appropriately. By providing speech level detectors, the
circuit operates in a hands-free mode, eliminating the need for a push-to-talk
switch."
"The MC65118 provides the necessary level detectors, attenuators, and
switching control for a properly operating speakerphone... (and) provides
background noise monitors which make the circuit insensitive to room and line
noise, hybrid amplifiers for interfacing to Tip and Ring [i.e. the phone line], the
microphone amplifier and other functions....."
OPTIONAL BATTERY OPERATION:
The use of a battery is optional for speakerphone operation but is required for
the Intercom operation described in the next section.
The use of a battery in speakerphone operation can compensate for abnormally
low telephone line voltage which may occur when a phone connection is at the
far end of the local "loop" connecting your location to the phone company's
central office. The supplementary battery can reduce the "pumping" effect
caused by incoming voice peaks.
IMPORTANT: Use a battery for this purpose, not a DC power supply.
It is
important to remember that the telephone line loop voltage is a minus 48 volts
DC with respect to earth ground.
Introducing a common AC mains ground at the
phone line input may damage SP1 components.
Содержание SP1
Страница 6: ...SP 1 6 SP 1 PARTS LAYOUT DIAGRAM...
Страница 12: ...SP 1 12 SP1 SCHEMATIC DIAGRAM...
Страница 22: ...SP 1 22 PARTS LAYOUT DIAGRAM SP1 SPEAKERPHONE KIT...