Table of Contents
Advertisement
When an optional TONE SQUELCH circuit is incorporated, the squelch
circuit opens only for the signals which accompany the preset TONE
signal with SQUELCH control at TONE position.
The 455 kHz output from Ql06, 2SC372Y is also applied to the
S-meter rectifiers, Dl0l
and
Dl02, 1Sl88FM.
The diodes rectify
the signal and the resulting DC voltage is applied to the meter where
it provides an indication of relative signal strength.
The S-meter
control, VRl0l, permits the meter circuit sensitivity to be adjusted.
TONE BURST CIRCUIT
The tone burst circuit consists of a timing generator and a gated
multivibrator.
When the BURST switch is set to the "ON" position,
the DC voltage is applied to Q214, SN7400N.
The transmitter,
"keyed'' at +13,5 volts DC is applied to Q213, 2SC372Y to trigger
the 4
-
gate NAND logic timing generator.
The timing generator
produces an output pulse applied to the multivibrator which produces
a tone output that is applied to the microphone input of the transmitter
section.
The tone frequency is adjustable between 1300 and 3000 Hz
PY VR206, while the output level (deviation) is adjustable by VR207
and the burst duration by VR205.
TONE SQUELCH CIRCUIT
(Optional)
The Tone Squelch operation permits private communications
on crowded channels.
The tone squelch circuit disables the
audio circuit of receiver until a preset tone signal is received.
The transmitted signal is modulated by the tone signal within
70 Hz to 250 Hz which is below the 300 Hz to 3000 Hz voice
frequency range used in radio communications.
The tone signal is generated by Q502, NE5 67 and its frequency
is set by R516, VR502 and C516.
The level of the tone signal
is set by VR504 and it is fed through a buffer amplifier, Q503,
2SK19GR to the low pass filter consisting of unit "d
II
of an
operational amplifier Q501, MC3403.
The tone signal is then
superimposed to the speech signal by Q202.
The constants for
preset frequency are obtained from the chart.
The audio output signal from the receiver discriminator is fed
to the unit "a
11
of Q501, MC3403.
The unit "a" of Q501 forms
a high pass filter and the unit
11
b'
1
of Q501 forms a T-notch filter.
Both filters remove the tone signal from the audio signal which
is then fed through an audio amplifier Q505, 2SC372Y to the
•
receiver audio amplifier Ql 11.
-
16
-
Advertisement
Table of Contents
