Ramsey Electronics SP1, Руководство пользователя

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SP-1
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battery connection. If the battery improves performance, then continue
using it for that particular location. It is switched in and out of the circuit by
the "B" section of S1.
C. Finally, you may encounter situations where the person on the other
end just is not speaking loud enough for positive SP1 switching between
receive and transmit. This can be caused either by the other party's use of
a poor-quality phone or just because they are speaking too softly. You may
need to ask them to try a different phone, or to just speak up or to speak
more directly into their handset microphone. Or, redial for a better
connection.
UNDERSTANDING SPEAKERPHONE OPERATION:
Because we take telephones so much for granted, it is easy to not care or
appreciate the many functions and features of the SP1 and the MC65118 IC.
That's OK: if it's working fine, then just enjoy it and don't worry about how it
works. However, since its operation characteristics will seem different from a
conventional handset telephone, you may get more satisfying use from your
speakerphone if you have at least some grasp for what it is accomplishing.
The easiest way to appreciate the functions of the MC65118 is to go through
the exercise of designing a two station speakerphone system in your head or on
a sketch pad. Both stations must have speakers and sensitive microphones and
be interconnected by two wires only, and there can be no manual talk-listen
switches. You must be able to turn the speaker up to normal room volume, and
the microphone circuit must be sensitive enough for you to speak from
anywhere in a small room. How would you do it? Remember: no switches just
two wires, and no squealing "feedback"!
The more we ponder how we would "easily rig up " such a system using a $1
amplifier chip, the more impossible it will seem, and the more we start to
appreciate the actual functions of true speakerphone technology. To put it very
simply, the speakerphone is "smart": it knows when to be idle, when to transmit,
when to receive, when to mute, when to attenuate, what to do about
background noise. It even recognizes the difference between steady
background noise and the phone line's dial tone.
Motorola explains the MC65118 this way: The fundamental difference between
the operation of a speakerphone and a handset is that of half-duplex versus full-
duplex. The handset is full duplex since conversation can occur in both
directions (transmit and receive) simultaneously. A speakerphone has higher
gain levels in both paths and attempting to converse full duplex results in
oscillatory problems due to the loop that exists within the system. The loop is
formed by the receive and transmit paths, the hybrid, and the acoustic coupling
(speaker to microphone.)