Technical data

B KY 96A, KY 97A
Rev 5, Apr 2003 MM 006-05674-0005.dwd Page 4-7
4.3.2.6 Digital Buffer
Q106, Q107 and their associated parts form the digital buffers. The VCO is very lightly
coupled to the digital buffers through C147 so that noise from the pre-scaler will not
get back to the VCO. The signal is coupled to the pre-scaler through C140 at about
500 mV.
4.3.2.7 Transmit Buffers
The transmit buffers contain two stages of amplification. The RF signal is coupled
through C155 to Q110 and amplified. C157 couples the collector of Q110 to Q126.
Q126 amplifies the signal to approximately 24 dBm. The signal is coupled through
CR117 and C228 to create the transmit drive. The drive level is adjusted for different
transmitters by the resistor R1006. Q111 and Q139 are turned off during receive al-
lowing Q110 and Q126 to be reversed biased. Q127 is also turned off during receive
preventing CR117 from being turned on. During receive the RF signal is reduced by
50 dB.
4.3.3 Modulator
4.3.3.1 Microphone Input Circuit
The microphone is connected to pin K of the rear panel connector. Mic bias is supplied
by R114 and R223. The signal passes through C191 to the Mic Gain control. Q119
is turned on during transmit to pass the signal to the modulator compressor.
4.3.3.2 Modulator Compressor
The audio signal is coupled through C230 to the input of the compressor amplifier,
I113A. The output is fed to the modulator amplifier, I113B will begin to discharge C198
when the output of the modulator exceeds the voltage across R267. Discharging
C198 lowers the gate to source voltage on Q120, which reduces the drain to source
resistance on Q120. As Q120 is turned on the amplitude at C230 is reduced. This
maintains a constant amplitude out of the compressor amplifier. R267 set the modu-
lation level. The bias network R257 and R267 is run off of the mod bias voltage, so
that when the mod bias sags the modulation will decrease preventing distortion.
4.3.3.3 Modulator Amplifier
The output of the compressor amplifier is coupled to the modulator amplifier through
C194. The output is coupled to the modulator through C196 and T108.
4.3.3.4 Modulator Bias
The modulator bias (mod bias) regulates the supply voltage to just below half the sup-
ply voltage. Q123 is the regulating transistor and on the 28 volt versions Q122 is used
to buffer the regulating transistor. The KY 96A drops the modulator bias an additional
6.2 volts through CR123. R251, R254, and R256 set the regulated voltage, with R256
being adjustable. CR115 prevents overvoltage problems. RT101, R250, and R252
set the power reduction due to a thermal overload. When RT101 becomes hot, the
resistance goes up reducing the voltage at E113, causing CR114 to turn on, and thus
lowers the bias on Q123.