User's Manual
2650 Watt VHF High Band Transmitter Chapter 4, Circuit Descriptions
435B, Rev. 0 4-25
occurs, the AGC Control Board generates
a Fault Output at J1 that is connected to
J4 on the Filter/Amplifier Board. The
Fault cuts back the RF Signal level using
the Pin Diode Attenuator Circuit located
on the Filter/Amplifier Board.
The output at J2 of the Phase Shifter
Board is directed to J1 the input jack on
(A2) an enclosure that contains the
filter/amplifier board and the high band
driver pallet.
4.2.2 (A2-A1) Filter/Amplifier Board
(1301178; Appendix D)
The phase controlled output of the Phase
Shifter Board (+7 dBm pk-sync + aural)
is directed to the (J7), the Input Jack of
(A2-A1) a Filter/Amplifier Board
(1301178) which is made up of two
circuits.
The first circuit is a Channel Filter that is
adjusted for the desired Channel
Frequency and bandwidth. The filtered
output is connected to the second circuit
that contains two amplifiers. The RF
connects through a Pin Diode Attenuator
Circuit to an amplifier IC U1. The
amplitude of the RF Signal through the
Pin Diode Attenuator Circuit is controlled
by the voltage applied to J4 the External
Control Jack of the Board. The Jumper
W1 on J5 should be between Pins 2 & 3
which provides for external control thru
J4 of the Gain of the Board and therefore
the Output level of the Tray. The front
panel mounted Gain Pot (R3) connects to
the AGC Control Board and adjusts the
AGC Pin Attenuator Bias Voltage that
connects to J4 on the Filter/Amplifier
Board.
The RF signal, after the Pin Attenuator
Circuit, is amplified by the second
amplifier stage (Q1) to about +12 dBm
pk-sync + aural that is connected to the
output of the board at J2.
4.2.3 (A2-A2) High Band Driver
Pallet (P-10-VHF-H; Appendix D)
The RF output of the Filter/Amplifier
Board connects to J1 on (A2-A2) the High
Band VHF Driver Pallet (P10-VHF-H)
made by Delta RF Technology. The
board contains a RF Power FET that has a
gain of approximately 20 dB.
The RF output of the Board at J2 (+31
dBm pk-sync + aural) connects to J2 of
(A3) a RF enclosure, which contains the
Overdrive Protection Board, the High
Band Amplifier Board and the 3 Way
Splitter Board.
4.2.4 (A3-A1) Overdrive Protection
Board (1198-1601; Appendix D)
The signal is connected to J4 of (A3-A1)
the Overdrive Protection Board (1198-
1601).
The RF Signal is thru connected directly
to J5 the RF Output Jack of the Board. A
sample of the RF on the board is applied
to a diode detector circuit consisting of
CR1 and U1A. The gain of amplifier U1D
is controlled by the Detector Gain Pot
R11 which is set to +.4 VDC as measured
at TP1. The set output level of U1D is
connected to the comparator IC U1B.
The Trip Point for the comparator is
adjusted by R12, typically to 110%
Output Power. When the signal reaches
that level, the Overdrive Protection Board
will cut back the output power of the
Tray and the Red Overdrive LED (DS1)
located on the Board and the Red
Overdrive LED (DS1) mounted on the
front panel will light. Typically the output
power level, will bounce Down, then Up
in level and continue bouncing until the
Output Level is lowered to normal
operating level, 100 %. The Red
Overdrive LED (DS1), the Green Module
LED (DS3) and the Enable LED (DS2)
may blink On and Off during the
bouncing of the output level and is a
Normal occurrence. The greater the
output level is above 110 %, the larger
the bounce.