User's Manual

3300-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions
335B, Rev. 0 4-23
J8-37 for the connection to a remote
VSWR cutback indicator.
4.1.8.8 Receiver ALC Fault
If a receiver tray is part of the system, a
sample of the ALC voltage from this tray
is connected to J8-11 on the transmitter
control board. If the receiver is
operating normally, the ALC level that is
applied to U3C pin 9, remains below the
trip level set by R35; as a result, the
output at pin 13 stays high. The high is
applied to the red ALC Fault LED DS8,
which is off. The high also connects to
U3A pin 2, and to Q15. Q15 is biased on
and the drain goes low. The low
connects to U5B, pin 6. In addition, U5B
normally has a low that is connected to
U5B, pin 5, and produces a high at
output pin 4. The high is wired to Q18,
which is biased on, and makes its drain
low. The low connects to U3D pin 12,
which, because the level is below the
preset, the output at U3D pin 14 goes
low. A low at this point indicates a no-
fault condition. The high that is
connected to U3A pin 2, causes its output
to go low. The low is connected to Q25,
which is biased off. The low is removed
from J8-12, which will not light any
remote receiver fault indicator that is
connected to it.
If the receiver malfunctions, the ALC
level applied to U3C pin 9 goes high. This
is above the level set by R35 and causes
the output at pin 13 to go low. The low
is applied to the red ALC Fault LED DS8,
which lights. The low also connects to
U3A pin 2 and to Q15. Q15 is biased off
and the drain goes high. The high
connects to U5B pin 6 that produces a
low at output pin 4. The low is wired to
Q18, which is biased off and makes its
drain go high. The high connects to U3D
pin 12 and, because the level is above
the preset, the output at U3D pin 14
goes high. A high at this point indicates
a fault condition that switches the
transmitter to Standby. The low
connected to U3A pin 2, causes its output
to go high. The high is connected to
Q25, which is biased on and causes the
drain to go low. The low is connected to
J8-12, which can light any remote
receiver fault indicator that is connected
to it.
4.1.8.9 Metering
The front panel meter connects to J3-1
(-) and J3-2 (+), the output of switch S3,
on the transmitter control board. The
front panel meter has seven metering
positions, which are controlled by S3.
They are the Audio level, Video level, %
Aural Power, % Visual Power, %
Reflected Power, % Exciter Power, and
ALC level. A sample of the video
connects to the board at J5-4 and is
connected through the video calibration
pot R20 to position 6 on front panel
meter switch S3. An audio sample enters
the board at J5-6 and is connected
through audio calibration pot R19 to
position 7 on front panel meter switch
S3. A reflected sample connects to the
board at J2-9 and is connected through
buffer amplifier U1B and 100Ω resistor
R84 to position 3 on front panel meter
switch. A visual sample connects to the
board at J2-5 and is connected through
buffer amplifier U1D and 100Ω resistor
R86 to position 4 on the meter switch.
The aural sample connects to the board
at J2-7 and is connected through buffer
amplifier U1C and 100-watt resistor R85
to position 5 on the front panel meter
switch. An exciter sample connects to
the board at J2-3 and is connected
through the buffer amplifier U1A and the
100Ω resistor R87 to position 2 on the
front panel meter switch. An ALC sample
connects to the board at J6-1 and is
connected through the buffer amplifier
U2C and the ALC calibration pot R15,
which adjusts the output of U2A pin 1,
and through the 100Ω resistor R18 to
position 1 on front panel meter switch.
Typical readings on the meter are:
• Video = 1 Vpk-pk at white
• % Reflected = < 5%
• % Visual power = 100%