Appeal No. 2001-2270
Application 09/235,529
lines 41-45). However, Stevens does not disclose that the
attenuation should be "at least 30 dB." Stevens discloses that
the AC (alternating current, also abbreviated "a.c.") shunt may
include a low impedance (less than 1/3 the impedance of the
telephone device) across the tip-ring wires (col. 6, lines 8-13).
Appellants state that this corresponds to an attenuation of only
8 dB (Br6), although no explanation of how this is calculated or
the effect of "less than 1/3" is presented. Stevens discloses
that an alternative, or additional, way to ensure that the
central office does not detect the DTMF codes is to jam the DTMF
codes by introducing an interfering tone (col. 2, lines 30-34;
col. 6, lines 20-33).
The attenuator in Stevens serves the same purpose as
appellants' claimed a.c. load, i.e., the load is chosen "such
that DTMF signals, for example, generated by telephones 30 or 32
are attenuated to a level at which the central office 5 will not
recognize the tones as valid" (spec. at 8, lines 1-3).
Appellants discuss that both serial-connected and
parallel-connected call function devices were known in the prior
art (spec. at 2, lines 3-18). However, serial-connected devices
often required an experienced technician for installation to work
with several telephones (spec. at 2, lines 3-8). Known parallel-
connected devices placed an a.c. load in parallel across the tip
and ring conductors so that dialing signals generated by the
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