KDK FM-2016A - Page 16

audio output fromthe discriminator is amplified and normal reception through the
speaker takes place.
5) RCV LED Circuit: -- The base voltage of audio amplifier Q14 is amplified by
two stages of direct coupled transistors, Q13 and Q12, and drives the RCV LED via
pin 24. This LED provides an indication when an incoming signal is being received
even if the volume control is turned completely off, or when using the transceiver
in conjunction with a KDK SC-12A or SC-10 SEL-CALL unit.
6) Discriminator Meter Circuit: -- DC output from the discriminator is amplified
by the differential d-c amplifier Q15 and Q16 and is applied to the RIT VR through
pins 21 and 22. It then drives the discriminator meter to providean indication of
the incoming signal's frequency. vR6 is the "zero balancer" for the differential
amplifier and should be adjusted so that the meter reads zero after first ground-
ing the gate of FET, Q16.
7) Transmitter Circuitry: -- The transmitter is a single conversion, narrow band
FM transmitter using direct modulation of the VCO (127.1 - 132.095MHz) which in turn
is controlled by the PLL.
8) Microphone Amplifier: -- Audio from the microphone enters the transmitter
through pins 8and9 and is then fed to the amplifier, IC-3 through the gain control,
VR7. C113 and the input impedance of IC-3 combine to provide pre-emphasis. Output
from the amplifier/limiter is passed through a 3KHz low pass filter, C120, L27 and
C121 to remove harmonics created by clipping and is then fed to the modulator vari-
cap in the VCO circuit via pins 10 and 1l.
9) Multi-purpose Tone Oscillator: -- IC-4 and 927 is the tone oscillator. 2 NOR
gates of IC-4 make upamultivibrator. Its oscillating frequency is determined by
C124, C125, R104 and VRIO. (See values tabulated versus frequency in 4. i). Output
from the oscillator is fed viapinll toalow pass filter R103, C123 to remove har-
monics created by the multivibrator. This filtered output is bufferred by 927 and
then fed to the low pass filter of the microphone amplifier through the level con-
trol, VR9.
The circuit can provide either a sub-audible tone or a higher frequency tone burst.
It can further be switched to provide either a continuous tone for the duration of
the transmission ora short burst atthe beginning of each transmission by operation
of the internal switch mounted on the Main Unit PCB.
The oscillator is controlled by the voltage applied by the TONE/RF ATT switch through
pin 46. For the tone burst, C128, R108 and 2 NOR Gates of IC-4 make upa "one shot
multivibrator" with a period of approximately .5 seconds.
The FM-2016A transceivers are set at the factory for a sub-audible tone of 100Hz
and the FM-2016E transceivers are set for a 1750Hz tone burst.
10) APC Circuit (Output Control): ~- RF power is sampled by the diode D2 in the
power booster module and is fed to the d-c amplifier 924 and 025 via pin 37. The
signal is then applied to the base of a buffer, Q21 and by varying the base voltage
controls the output. VR3 sets the low power output and VR4 sets the high power out-
put through the main power switch and pins 14, 15 and 27. The unlock signal from
the synthesizer unit is applied to the APC through pin 27.
11) Transmitter Exciter: ~- Transistor Q17 and crystal X2 combine to generate a
16.9MHz signal which is amplified by 018 and is fed to the balanced mixer Q19 and
Q20 through tuned circuits L15 and L16. The TX local oscillator signal from the
synthesizer unit is also applied to the mixer through pins 6 and7. (127.1 - 132.095MHZ).
The mixer converts these inputs to the desired signal frequency (144.0 - 148.995).
This output is passed through 4 sucessive stages of electronic tuned circuits,
inductors L18, L19, L20, L21 and varicaps D14, D15, D16 and D17 which are peaked
at the operating frequency to minimize spurs. This circuit is similar to the cir-
cuits employed inthe receiver and are effective in attenuating all but the desired
frequency. The output is amplified by a dual gate MOS-FET, Q21 and passes through
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