Pulsar TCF-10B, System Manual, Page: 218 / 249

18.4 Voice Adapter Circuit
Description
18.4.1 Receiver
The RF input to the Voice Adapter is a 5.02-MHz
IF signal from the Receiver Module, which is
filtered by FL1, amplified by Q1, and input to I1
(an AGC amplifier). The I1 output is filtered by
FL2, with Q2 operating as a buffer to drive the
AM Detector (I2), which provides a demodulated
audio output, plus a dc signal as input to the
comparator (I3/1,2,3). Potentiometer R41
provides an adjustable reference and is factory set.
The output of I3 controls the gain of the AGC
amplifier (I1).
The audio output (from I2) will be squelched by
the Audio Squelch circuit (I6) if the RF input
(5.02 MHz) is below -85 dBm. This is accom-
plished by comparator (I3/5,6,7) which monitors
the AGC central voltage (see Figure 18-3).
The audio output will also be squelched, with
jumper JU1 “IN”, when the transmitter is keyed.
The front panel potentiometer RECEIVER
AUDIO (R24) provides for field adjustment of the
Receive Audio level when you adjust the input
level to Audio Output Amplifier (I3/8,9,10). This
amplified output is passed through an output
protection circuit (R34, Z1) to the HANDSET
jack (TJ1), or to a remote handset connected to
terminal block (TB5) on the rear panel.
18.4.2 Audio Transmit
The Current Limiter, comprising Q4, Q5, and R72
(see Figure 18-3) provides approximately 22 mA
to the handset microphone, when the push-to-talk
switch in the handset is pushed. Front panel poten-
tiometer MIC. SENS (R63) provides for
adjustment of the level of audio voice signals from
the microphone. These signals are input to the 2.2
kHz lowpass filter (I4/1,2,3), which attenuates
frequencies above 2200 Hz. The output of I4 is
input to the Output Limiter (I4/12,13,14),
according to the following conditions:
• If JU2 is “OUT”, input to I4(13) is direct
• If JU2 is “IN”, input to I4(13) is through
compressor (I5)
I4 outputs (through pin A-28) provide a maximum
signal of 3.2 Vp-p into the 600 ohm input
impedance of the Transmitter Module.
18.4.3 TC–10B/TCF–10B Signaling
Jumper JU4 selects either the TC–10B or the
TCF–10B signaling operation.
TC–10B Signaling
Set jumper JU4 to the “TC” position. Also set
jumper JU5 to “NC”.
Initiate signaling by pressing the push-to-talk
switch on the handset. Signals are detected by I7
and Q6, which signal a Voice-Key level to the
Keying Module.
You may terminate ringing in two different ways
(depending on the configuration used at the other
end of the system):
1. By plugging the handset into the front panel
“HANDSET” jack of the Voice Adapter
Module, Relay K-1 is energized, illuminating
the front control panel LED “Alarm/Alarm
Cutoff”; the normally-closed contacts are
opened and the alarm is interrupted.
2. When using a remotely-connected handset.
The alarm contacts from the Voice Adapter
(TB5) are wired in series with the Level
Detector (TB2) contacts. When a carrier
signal is received from a remote system, Level
Detector (TB2) contacts close, providing an
alarm signal. You can interrupt the alarm in
the following ways:
• By plugging the handset into a jack, which
is connected remotely to the TC–10B rear
panel (TB5); the jack contacts interrupt the
alarm (see Figure 18-4, top scheme)
• By lifting the handset from the hookswitch
assembly, which is connected remotely to
TB5; the hookswitch contacts interrupt the
alarm (see Figure 18-4, bottom scheme)
TCF–10B Signaling
Set jumper JU4 to the “TCF” position. Also, set
jumper JU5 to the “NO” position.
Page 18–4 April 1997
TCF–10B System Manual
Technologies, Inc.