PLL (Phase Lock Loop) CIRCUIT DESCRIPTION
The PLL (Phase Lock Loop) circuit used in the
TRC-457 consists of 6 majorcomponents; Voltage
Controlled Oscillator (VCO), 1/N Divider, Refer-
ence Oscillator, 1/1024 Divider, Phase Detector
and Low Pass Filter.
The VCO is an oscillator which controls oscilla-
tion frequency in accordance with input voltage
changes. The VCO output is mixed with a signal in
the transmitter or receiver circuitry. A portion of
the VCO frequency is fed to FET4 and mixed with
a 33.8525 - 33.8575 MHz frequency from X3, X4
or X6 and then goes through TR30 Amplifier and
TR31 Buffer Amp and then added to the 1/N
Divider. This is applied to one input of the Phase
Detector. "N" for the 1/N Divider is determined
by the Channel Selector Switch (by BCD) and
varies from 91 to 135.
On the other hand, a 10.24 MHz frequency from
the Reference Oscillator is divided to 10 kHz by
1
/
1
024 Divider and applied to another input of the
Phase Detector. The Phase Detector detects the
difference of these two input signals and produces
a voltage which controls the VCO frequency. The
Low Pass Filter integrates the outpuf voltage of
the Phase Detector which controls the VCO
frequency and the 1/N Divider produces a 10 kHz
frequency.
Thus the Phase Detector receives two input signals
(both 10 kHz). It compares the phase difference of
the two, generating an error voltage, which acts on
the VCO to bring the two frequencies exactly in-
phase. When this condition occurs, the PLL circuit
is "locked".
WAVE FORM Of IC7
Note: Pin No. 13 through 18, 20 & 21 are as in frequency
chart.
Pin No. 19, 22 & 23 are fixed to Low level.
By varying the constant N, the output frequency
from the VCO can be locked and varied one
10 kHz step at a time. The constant N is controlled
by the Channel Selector Switch. A frequency shift
of 2.5 kHz (required for AM RX, USB and AM TX
and LSB RX/TX) is obtained by switching to X3,
X4 or X6 as shown in Frequency Chart.
For a more detailed description of how this circuit
functions, refer to Abbreviated Block Diagram as
well as the full Block Diagram and Schematic.
