Assembly Instructions Chapter 4

4-6 kW UHF Translator Chapter 4, Circuit Descriptions
837B, Rev. 0 4-27
4.2.10 (A13) (Optional) EEPROM
FSK Identifier Board (1265-1308;
Appendix D)
The optional FSK identifier board, with
EEPROM, generates a morse code
identification call sign by frequency-
shift keying the VCXO oscillator in the
upconverter or by sending a bias
voltage to the IF attenuator board to
amplitude modulate the aural carrier.
This gives the station a means of
automatically repeating its identification
call sign, at a given time interval, to
meet FCC requirements.
The starting circuit is made up of U1B
and U1D, which are connected as a
flip-flop, with gate U1A used as the set
flip-flop. U1A automatically starts the
flip-flop each time U3 completes its
timing cycle. At the start of a cycle,
U1B enables clock U2. U2 applies the
clock pulses that set the speed, which
is adjusted by R2, for when the
identification code is sent to 12-bit
binary counter U4. R2, fully clockwise
(CW), is the fastest pulse train and R2,
fully counter-clockwise (CCW), is the
slowest pulse train. U4 provides binary
outputs that address EEPROM U5.
The scans in U4 will continue until field
effect transistor (FET) Q1 is gated on.
The gate of Q1 is connected to pin 13
on U4, which is the maximum count
used in the EEPROM, and will provide a
reset pulse each time the binary
counter goes high on pin 13. The reset
pulse, when the drain of Q1 goes low,
is applied to the flip-flop and the timer
U3, which determines the length of
time between the sending of the
identification code. R14 is adjusted to
set this time interval. R14, fully CW, is
the longest interval between
identification calls, approximately eight
minutes. R14, fully CCW, is the
shortest interval between the sending
of the code (approximately 10
seconds).
U6B is an amplifier connected to the
output of U5, which turns the LED DS1
on and off at the rate set by R2. This
gives the operator a visual indication
that the FSK identifier board is
operating and at the rate at which it is
operating.
The data output of U5, which is serial,
is connected to U6A, whose output
shifts low and high, and is applied to
the VCXO board, which shifts the
frequency according to the
programming of U5. The deviation of
the shift is adjusted by R4 and is
typically set at 1 kHz. Once R4 is set,
R9 is re-adjusted to -1.5 VDC at J3-2.
The +12 VDC from an external power
supply enters the board at J1, pin 3.
The voltage is fed through RF choke L1
and is filtered by C1 before being
applied to the rest of the tray. The +12
VDC is also applied to U7, which is a
voltage regulator that regulates its
output at +5 VDC. The +5 VDC is fed
to the ICs on the board. The -12 VDC
from an external power supply enters
the board at J1, pin 5. The voltage is
fed through RF choke L2 and filtered by
C2 before being applied to the rest of
the tray.
4.2.11 (A24) (Optional) Composite
4.5-MHz Filter Board (1227-1244;
Appendix D)
The composite 4.5-MHz filter board is
mounted in the UHF exciter tray and is
part of the composite 4.5-MHz input
kit. The board filters the 4.5-MHz
composite signal to produce a video-
only output that connects to the sync
tip clamp/modulator board.
The composite 4.5-MHz signal from the
sync tip clamp/modulator board enters
the board at J1 and is amplified by U1A
and then split. A sample of the
composite 4.5-MHz signal is connected
out of the board at J2 and connects to
the 4.5-MHz bandpass filter board. The
other split portion of the composite 4.5-