User's Manual

2650 Watt VHF High Band Transmitter Chapter 5, Detailed Alignment Procedures
435B, Rev. 0 5-11
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 R20 (two 1Ω
resistors in parallel on the filter/amplifier
board) and adjust R13 for .125 volts
(using Ohms’ Law: [E=I x R] : [E=250
mA x .5 Ω] : E=125 mV).
5.2.4 (A2-A2) VHF High Band
Amplifier Board (P10-VHF-H;
Appendix D)
This board is supplied by Delta RF
Technology, Inc. Refer to the data
sheets in the subassembly section of this
manual for more information. The board
has approximately 19 dB of gain and the
output is typically +31 dBm.
5.2.5 (A3-A1) Overdrive Protection
Board (1198-1601; Appendix D)
The level of the RF input and output of
the (A3-A1) overdrive protection board
(1198-1601) should be +31 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 110%, sync only, and adjust R12 until
the output power begins to drop off.
Return the output power level of the
transmitter to 100%.
5.2.6 (A3-A2) VHF High Band
Amplifier Board (P200-VHF-H;
Appendix D)
This board is supplied by Delta RF
Technology, Inc. Refer to the data
sheets in the subassembly section of this
manual for more information. The board
has approximately 14 dB of gain and the
output is typically +45 dBm.
5.2.7 (A3-A3) 3 Way Splitter Board
(1301161; Appendix D)
This board contains no tuning
adjustments. The board takes the +45
dBm input and splits it into three equal
+40 dBm outputs.
5.2.8 (A4-A1 thru A3) VHF Output
Amplifier Pallets (P400-VHF-H;
Appendix D)
These boards are supplied by Delta RF
Technology, Inc. Refer to the data
sheets in the subassembly section of this
manual for more information. Each
board has approximately 13 dB of gain
and the output is typically +53.3 dBm.
5.2.9 (A5-A1) 3 Way Combiner
Assembly (1301157; Appendix D)
There are no adjustments to the (A5-A1)
3 way combiner assembly. The three
+53.3 dBm inputs are combined to
produce the 750 watts peak of sync +
aural output (+57.8 dBm) at the RF
output jack J5 of the combiner.
J5 of the combiner connects to J2 the RF
Output Jack of the VHF Amplifier Tray.
5.2.10 Calibration of the Visual Plus
Aural Output Power and VSWR
Cutback of the VHF amplifier tray
Check that a dummy load of at least 750
watts is connected to the output of the
tray that is to be calibrated. Place switch
S1 on the AGC control board in the
Manual position before beginning the
setup.
To adjust the visual output power levels:
1. Remove the J16 cable from (A5) the
sync tip clamp/modulator board
(1265-1302) in the exciter tray. Set
Manual AGC switch S1, on the (A13)
AGC control board (1142-1601) in the
VHF amplifier tray, to the Manual
position.
2. Connect a sync and black test signal
to the video input jack of the remote