Specifications

A.6.3 SYNTH PAL
The SYNTH PAL U11 has four main functions, Band Switch
Logic, BCD to Binary Conversion, Digit Shifting,and Frequency
Fault Detection.
Refer to Figure A-1 for the following discussion.
A.6.3.1 Band Switch Logic
The 3 Most Significant Groups of MSD inputs (MSD, 2MSD,
and 3MSD) are connected to the Band Switch Logic. This circuit
reads the BCD input codes and is basically used asdecoder which
produces the following outputs:
If a Low Band frequency has been selected:
a. The Band L output will be a logic low, enabling the Low
Band buffers of U6, U2, and U1.
b. The Band H output will be a logic high, disabling the High
Band Buffers of U6, U2, and U1.
c. The Range 1 output will be a logic low, allowing the
Synthesizer to operate in the 525 to 1599 kHz frequency
range, and this also disables the Digit Shifter.
If a High Band frequency has been selected:
a. The Band L output will be a logic high, disabling the Low
Band buffers of U6, U2, and U1.
b. The Band H output will be a logic low, enabling the High
Band Buffers of U6, U2, and U1.
c. The Range 1 output will be a logic high, allowing the
Synthesizer to operate in the 1600 to 1605 kHz frequency
range, and this also enables the Digit Shifter.
A.6.3.2 Frequency Fault Detector
The Frequency Fault Detector’s function is to read the same BCD
program switch information as the Band Switch Logic and to
produce a Synthesizer Fault if the selected frequency is out of the
525 to 1605 kHz range of the transmitter. This fault will apply
an RF Mute to the transmitter and illuminate the corresponding
LED RED on the Frequency Control Panel.
A.6.3.3 BCD To Binary Converter And Digit Shift
The2 Most SignificantGroups of MSD inputs (MSD and 2MSD)
are connected to the BCD To Binary Converter. This circuit reads
the2-4 Bit BCD input codes andconvertsthem to the 4 Bit Binary
MSB output to the Digit Shift.
The Digit Shift output to the Synthesizer is dependent upon the
Range 1 output from the Band Switch Logic.
a. If the Range 1 output is a logic low (Low Band operation),
the Digit Shift output will be the same output as from the
BCD To Binary Converter. This output range is therefore
from 1 to 15 depending upon the frequency selected.
b. If the Range 1 output is a logic high (High Band operation),
the Digit Shift output will be 1 only.
A.6.4
Tri-State Digit Shift Buffers
The Tri-State Digit Shift Buffers U6, U2, and U1 are used to
transfer the frequency selected BCD information to the appro-
priate Synthesizer Binary input depending on the band required.
When the enable input on pin 1 is a logic low, the IC functions
like a normal buffer. When the input is a logic high, all of the
output pins are an open circuit.
A.6.4.1 Low Band Digit Shifting
When a Low Band frequency has been selected, the Band Low
output of the SYNTH PAL U11-22 will be a logic low:
NOTE - All of the Low Band Buffers are active and all of the
High Band Buffers are disconnected.
a. The MSD 4 Bit and 2MSD 4 Bit input are connected to the
SYNTH PAL. The output of the Digit Shift inside the
SYNTH PAL is directly connected to the MSB 4 Bit
Synthesizer input.
b. The 3MSD 4 Bit input is connected to the 2MSB 4 Bit
Synthesizer input via the Data Latch U9.
c. The LSD 4 Bit input is connected to the 3MSB 4 Bit
Synthesizer input via the Data Latch U10.
d. The 100Hz Step Adjustment switch S1 is connected to the
LSB 4 Bit Synthesizer input via the Data Latch U10.
A.6.4.1.1 100Hz Step Adjustment
When in the Low Band, the 100 Hz Step Adjustment switch S1
supplies the LSB 4 Bit input to the Synthesizer. This is a manual
adjustment switch that is not part of the Frequency Select
switches, and allows fine XXXX.1 to XXXX.9 kHz frequency
selection.
Refer to Figure A-2, Band Switching Logic, for the following
discussion.
If a frequency of 0525 kHz (upper left corner) was entered on the
Frequency Control Panel Frequency Select switches:
a. The logic level of the BCD inputs is listed on the left side
of chart.
b. The logic level of the Binary inputs to the Synthesizer is
listed on the right side of the chart.
NOTE - In Low Band operation, the Decimal Point follows the
3MSB so the Binary input is 525.0 (100Hz Step Adjustment = 0)
If a frequency of 1599 kHz (upper right corner) was entered on
the Frequency Control Panel Frequency Select switches:
a. The logic level of the BCD inputs is listed on the left side
of chart.
Figure A-1
888-2339-002 A-3
WARNING: Disconnect primary power prior to servicing.