Technical data

B KY 96A, KY 97A
Rev 5, Apr 2003 MM 006-05674-0005.dwd Page 4-5
the input signal to the noise amp is shorted to ground, causing the noise squelch circuit
to be inhibited.
Transistor Q112 amplifies the noise from the collector of the detector and limits its am-
plitude so that impulse spikes (such as ignition noise) will not be of a higher amplitude
than other noise. The output of Q112 is coupled to a 8 to 10 kHz bandpass filter,
I106A. The output of the bandpass filter is fed to the comparator, I107A. The signal
is compared to the reference level set by R176. When the noise signal is larger than
the reference level the comparator goes high charging C166. If C166 is charged great-
er than half the supply voltage, then the unit will be squelched.
CR107A and CR110B will squelch the radio in transmit.
4.3.1.13 Squelch Gate
Q116, Q117 and associated parts make up the squelch gate. The audio signal comes
from the detector at TP108; the detector biases Q116. When the unit is squelched the
base of Q117 goes to the supply voltage and its emitter follows. Since the emitters of
Q116 and Q117 are tied together, Q116 becomes reverse biased; attenuating the sig-
nal 70 dB.
4.3.1.14 Audio Low Pass Filter
Inductor L110 and its associated capacitors form a low pass elliptical filter. The filter
is at least 20 dB down at 4 kHz and the notch is at least 25 dB down at 4.5 kHz. The
filter does roll off below 350 Hz since the signal is AC coupled in and out of the filter.
The low frequency roll off reduces 60 cycle hum.
4.3.1.15 Audio Compressor
The received signal is coupled through C178 to the input of the compressor amplifier,
I111A. The output is fed to the volume control and to I111B. I111B will begin to dis-
charge C179 when the amplitude to I111B exceeds the voltage across R210. Dis-
charging C179 lowers the gate to source voltage on Q118, which reduces the drain to
source resistance on Q118. As Q118 is turned on, the amplitude at C178 is reduced.
This maintains a constant amplitude out of the compressor amplifier.
4.3.1.16 Audio Amplifier
The audio signal is routed through the volume control R902 to the audio amplifier,
I112A. The signal is amplified approximately 30 dB and capacitive coupled through
C187 to the auto-transformer, T107. The voltage and impedance are stepped up to
provide a minimum of 100 mW of audio power into 500 ohm load; such as headphones
or an audio panel. The sidetone, through R220, and the Mic intercom, through R218,
are also amplified by the audio amplifier.
An optional 4 ohm audio amplifier provides 4 watts on 13.75 V units and 8 watts on
27.5 V units. See audio board section for more details.
4.3.2 Stabilized Master Oscillator (SMO)