User's Manual

2650 Watt VHF High Band Transmitter Chapter 4, Circuit Descriptions
435B, Rev. 0 4-24
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.
4.1.12 (Optional) (A4-A12) IF
Attenuator Board (1150-1201;
Appendix D)
The (Optional) IF attenuator board is
operated with the FSK identifier board to
produce an amplitude-modulated aural IF
signal for broadcasting the required FCC
station identification call sign at the
proper time intervals.
The board contains a pin-diode
attenuation circuit that consists of CR1
and the two resistors R2 and R3. The
bias output of the FSK identifier board is
applied to J3 of the IF attenuator board.
As the bias applied to J3 increases and
decreases, the amplitude of the aural IF
signal, which enters the board at J1 and
exits the board at J2, will increase and
decrease. This produces an amplitude-
modulated aural IF signal at J2, the aural
IF output jack of the board.
4.2 (A6 and A7) VHF High Band
Amplifier Trays (1301169;
Appendix C)
The On Channel RF signal (+3 dBm pk-
sync + aural), enters the rear of the
Tray at the "BNC" Jack J1 and is fed
through J1 of the (A1) Enclosure
Assembly to J1 of (A1-A1) the Phase
Shifter Board (1198-1603).
4.2.1 (A1-A1) Phase Shifter Board
(1198-1603; Appendix D)
The Board provides a Phase Shift
adjustment of the RF Signal that is
needed to provide maximum output
during the combining the two VHF
Amplifier Trays in the transmitter. A
front panel mounted Phase Shift
Potentiometer (R2), which connects to
J3 of the Board, controls the Phase of
the RF Signal.
If the Input Signal level to the Phase
Shifter Board falls below a preset level, a
High, which is an Input Fault, connects
from J5 of the board to J14 on the AGC
Control Board. When an Input Fault