User's Manual

Digital UHF Transmitter Chapter 4, Circuit Descriptions
DT835A, Rev. 1 4-27
by capacitor C1 and bypassed by C2 to
prevent oscillations. The filtered +12
VDC is applied to U1 a 7812 IC voltage
regulator and current limiter. C3 is a
bypass capacitor to prevent oscillations
in the output DC lines. DS1 is a Green
LED which when lit indicates that the
+12VDC is present at the output of the
board. The +12 VDC is distributed thru
Pins 2 & 7 of each of the Output Jacks,
J1, J2, J3 & J4, to the rest of the
boards in the Tray.
The -12 VDC is produced by using a
Full-Wave rectifier circuit that consists
of CR3 and CR4 whose output is filtered
by capacitor C4 and bypassed by C5 to
prevent oscillations. The filtered -12
VDC is applied to U2 a 7912 IC voltage
regulator and current limiter. C6 is a
bypass capacitor to prevent oscillations
in the output DC lines. C7 is a holding
capacitor to maintain -12VDC for an
instance even if the supply is lost. This
is to allow the positive voltages to be
removed from GaAs FET Amplifier
devices to prevent damage to the
devices. DS2 is a Green LED which
when lit indicates that the -12 VDC is
present at the output of the board. The
-12VDC is distributed to the rest of the
Boards in the Tray thru Pins 4 & 5 of
each of the Output Jacks, J1, J2, J3 &
J4.
The ±12 VDC outputs of the board are
connected to the rest of the boards in
the Metering Panel.
4.6 (A8) AC Distribution Assembly
(1245-1500; Appendix C)
The AC Distribution Assembly
distributes the Main AC Input, 208/240
VAC @ 20 Amps, that connects to the
UHF Exciter Assembly Cabinet to the
Trays and Assemblies which make up
the Exciter.
The 208/240 VAC Main AC Input to the
Exciter Cabinet connects to the
Terminal Block TB1, Line 1 to TB1-1A,
Line 2 to TB1-3A and Ground to TB1-
2A.
The 208/240 VAC Main AC Input
connects from the Terminal Block TB1-
1B (Line 1) to the 20 Amp Circuit
Breaker CB1-1, TB1-2B (Ground) to
Chassis Ground & TB1-3B (Line 2) to
the Circuit Breaker CB1-3. Three
MOVs, for surge and transient
protection, are connected to the AC
Lines from the Circuit Breaker, VR1 and
VR3 from the AC Lines to Ground and
VR2 across the AC Lines.
The switched 208/240 VAC Main AC
Input is wired from the Circuit Breaker
Terminal 2 to the L inputs and Terminal
4 to the N Inputs of the (A1 & A2) IEC
Outlet Strips. The E Inputs to both IEC
Outlet Strips connect to Chassis
Ground.
There are four outputs for both the
(A1) and the (A2) IEC Outlet Strips.
On the A1 Outlet Strip, J1 connects to
J14 on the (A1) Exciter #1, J2 connects
to J14 on the (Optional) (A2) Exciter
#1, J3 connects to J8 on the (Optional)
(A3) Exciter Switcher Tray and J4
connects to J2 on the (A4) Variable
Phase/Gain Tray. On the A2 Outlet
Strip, J5 connects to J2 on the (A5)
Variable Phase/Gain Tray, J6 connects
to J8 on the (A6) Metering Panel, J7
connects to J2 on the (Optional) (A7)
Receiver Tray or to the AC Input Jack
on the (Optional) Digital Modulator and
J8 is not used in this System.
4.7 (A2 & A3) 2-3 kW Amplifier
Array (1278-1300; Appendix C)
There are two Amplifier Array
Assemblies in the DT835A 2-3 kW UHF
Solid State Internally Diplexed Digital
Television Transmitter. The (A2 & A3)
Amplifier Array Assemblies (1278-
1300) are identical and configured
according to the output power needed.
Each Amplifier Array contains (A9-A1)
an 8 Way Splitter (ZFSC-8-43), four to