User's Manual

350-Watt Digital VHF LB Transmitter Chapter 5, Detailed Alignment Procedures
DT325B, Rev. 0 5-2
Remove the Sample Forward Power
connection J4 from the board. The
Output Power Level should drop to 20 %
because of the VSWR Cutback and DS4
should light. The front panel Module
Status LED should not be illuminated.
Reconnect J4 and adjust R59 to begin
cutting back the Output Power Level
when the Reflected Level increases above
20 %. The front panel Meter in the
Power Supply Voltage position is
calibrated to +32 VDC using R86 located
on the AGC Control Board.
5.3.2 (A1-A1) Phase Shifter Board
(1198-1602; Appendix D)
This board has no adjustments on it. The
Front Panel has adjustments for Phase
that are adjusted during the Amplifier
Array Set Up Procedure. With +4 dBm
input typical output is +4 dBm.
5.3.3 (A1-A2) Filter/Amplifier Board
(1198-1606; Appendix D)
This board has a maximum of 15 dB
gain. Typically with +4 dBm input an
output of +16.5dBm is expected. Tune
the channel filter capacitors C20 (input
loading) & C29 (output loading), C23 &
C26 (center frequency) and C24
(coupling) for best response at J6 the RF
output jack of the filter portion of the
board. Set the Voltage Adjust Pot R19
for +24 VDC at the Anode of CR5.
The idling current, no RF Drive applied, of
the Device Q1 is set for 250 mA. To set
the current, remove the RF Drive,
measure the voltage across R16, a 1 Ω
resistor on the Filter/Amplifier Board, and
adjust R13 for .25 Volts. Using Ohms
Law: (E = I x R) : (E = 250 mA x 1 Ω) :
E = 250 mV.
5.3.4 (A2-A1) VHF Low Band
Amplifier Board
(1198-1605; Appendix D)
This board has 20 dB of gain and is
biased for 3 Amps of Idling Current, no
RF Drive applied. To set the Bias,
remove RF Drive and switch the front
panel Current Meter to the I
D
position.
Adjust the Bias Adjustment R4 on the
Amplifier Board for 3 Amps on the meter.
Connect a Spectrum Analyzer to the
Output Jack J2 of the Board and adjust
C1 for peak output. Typical output level
is +38.5 dBm.
5.3.5 (A2-A2) Overdrive Protection
Board (1198-1601; Appendix D)
The RF Input and Output of the board
should be approximately +38.5 dBm
during normal operation.
To set up the Overdrive circuit, check
that the Output Power Level of the
Transmitter is at 100 % and adjust R11,
on the Board, for a reading of .4 VDC at
TP1. Increase the Output power level of
the Transmitter to 120 % and adjust R12
until the Output Power begins to Drop
Off. Return the Output Power Level of
the Transmitter to 100 %.
5.3.6 (A2-A3) 3 Way Splitter Board
(1198-1608; Appendix D)
This board contains no tuning
adjustments. The board takes the +38.3
dBm input and splits it into three equal
+33.3 dBm outputs.
5.3.7 (A3-A1, A2 & A3) VHF LB
Output Amplifier Pallets
(1304348; Appendix D)
These P400-VHF-LB pallets are supplied
by Delta RF Technology, Inc. Refer to
the data sheets in the subassembly
section of this manual for more
information. Each pallet has
approximately 18 dB of gain. With +33.3
dBm input an output of +51.3 dBm is
typical.