Specifications

Telephonics 77
B.4 Ring Detection
Ringer Equivalence
The DECvoice ring detection circuit has a ringer equivalence of .3B, as
determined by FCC test methods. The ring detection circuit has a load
number of 10 by DOC test methods.
Ring Characteristics
DECvoice detects rings with frequencies between 15.3 Hz and 68.0 Hz
and voltages between 40 and 150 volts rms.
B.5 Tone Detection
DECvoice can detect DTMF signals. DTMF signals are the signals that
a Touch-Tone phone creates. DECvoice cannot detect digipulse signals.
Digipulse signals are the signals that a rotary phone creates. A digipulse
phone has keys like a Touch-Tone phone, but does not create DTMF
signals.
Tone Frequencies
DECvoice accepts DTMF tones that are within ±1.5% (±2 Hz) of the
nominal frequency. DECvoice rejects DTMF tones that are outside of 3.5%
of the nominal frequency. DTMF tones are a combination of two tones,
one from the row group, and one from the column group.
The row group tones are 697 Hz, 770 Hz, 852 Hz, and 941 Hz, moving
from the top row (containing 1) to the bottom row (containing 0). The
column group tones are 1209 Hz, 1336 Hz, 1477 Hz, and 1633 Hz, moving
from the leftmost row (containing 1) to the rightmost row (containing 3).
The column group also includes the extra row of keys that are occasionally
present in PBX installations (often labeled A, B, C, and D).
Tone Timing
DECvoice is designed to recognize a DTMF tone that is present for at least
55 ms. DECvoice ignores a tone burst of less than 35 ms, interpretting it
as a noise burst. A DTMF tone should be absent for at least 55 ms before
it can detect the next DTMF tone. DECvoice ignores a tone that is absent
for 40 ms or less, interpretting it as a dropout.