Technical data

B KY 96A, KY 97A
Rev 5, Apr 2003 MM 006-05674-0005.dwd Page 4-4
The desired signal is coupled from T102 to the first IF amplifier, I101. The first IF am-
plifier has about 45 dB of gain with 60 dB of dynamic range. IF AGC voltage is applied
to I101 on pin 5 through R124. R124 converts the AGC voltage to an AGC current.
The output is loaded with R245 for stability. T103 is tuned for 11.4 MHz and couples
the signal to the second IF amplifier.
4.3.1.8 Second IF Amplifier I102
The second IF amplifier has about 45 dB of gain with 60 dB of dynamic range. IF AGC
voltage is applied to I102 on pin 5 through R126. R126 converts the AGC voltage to
an AGC current. The output is loaded with R246 for stability. T104 is tuned for 11.4
MHz and couples the signal to the detector.
4.3.1.9 Detector
Transistor Q105 and capacitor C130 makes up the amplitude modulation detector. It
is biased near cutoff by transistor Q104, which the emitter-base junction provides bias
stability and temperature compensation. The demodulated signal is sent to the noise
amp, Q112, IF AGC, I105A, squelch gate, Q116, and to the demodulator buffer, Q131.
4.3.1.10 IF AGC Circuit
AGC voltage is derived from the average value of the detector collector voltage, which
is inversely proportional to the carrier level. The operational amplifier I105A filters out
the audio variations and integrates to the average voltage of the detector. R159 and
R160 set the maximum gain reduction at about 6.6 volts. As the detector collector volt-
age increases with a decrease in signal level, the AGC voltage decreases which in-
creases the gain in the first and second IF amplifiers. The IF AGC voltage is made
available at TP105 and at the rear connector pin L. The AGC voltage at pin L is re-
duced by one diode drop (approx. 0.6 V).
4.3.1.11 RF AGC Circuit
The RF AGC voltage is applied to the RF amplifier from I105B. The RF AGC stays at
maximum voltage (maximum gain of amp) until the RF signal level reaches about 12.5
uV. The level at which it attacks is set by R184. When the IF AGC voltage exceeds
the reference voltage set by R184, the RF AGC voltage decreases, decreasing the
gain in the RF amplifier. RF AGC is made available at TP106.
The RF AGC is gated with TX(not) through CR120A such that when the unit transmits,
the RF AGC voltage goes to zero. This provides maximum attenuation in the RF am-
plifier during transmit.
4.3.1.12 Noise and Carrier Squelch Circuit
The carrier squelch circuit prevents the radio from squelching if an RF carrier greater
than 12.5 uV has been detected. I106B compares the RF AGC voltage, which is in-
versely proportional to the carrier level, to the reference level set by R183 and R185.
If the RF AGC voltage is greater than the reference level, then the unit is allowed to
squelch; if the noise level is large enough. When the RF AGC voltage is less than the
reference level, the output of I106B goes high; turning on Q140. When Q140 turns on,