User's Manual

300-Watt Digital UHF Transmitter Chapter 4, Circuit Descriptions
DT830A, Rev. 1 4-16
Auto/Manual switch S2 on the front panel
of the tray.
When the S2 switch is set to the Auto
position, the operation of the transmitter
is controlled by the fault circuits and will
stay in Operate even if Operate/Standby
switch S1 is switched to Standby.
With switch S2 in Auto, a low is applied
to one coil in the relay that energizes and
closes the contacts. The closed contacts
apply a low to the green Automatic LED
DS3, causing it to light. The low from the
relay connects to U5A, pin 2; U5D, pin
13; Q21; and Q23. Q21 and Q23 are
biased off, which causes their outputs to
go high. The high from Q21 connects to
the amber Manual LED DS4 on the front
panel, biasing it off, and to Q22, biasing
it on. The drain of Q22 goes low. The low
is applied to J8-7 and this will enable any
remote auto indicator that is connected
to it. The low to Q23 biases it off and
removes the enable to any remote
manual indicator connected to J8-6.
When switch S2 is set to the Manual
position, the operation of the transmitter
is no longer controlled by the fault
circuits; it is controlled by Operate/
Standby switch S1. With switch S2 in
Manual, a low is applied to the other coil
in the relay, which energizes and opens
the contacts. The open contacts remove
the low from the green Automatic LED
DS3 on the front panel, causing it to not
light. The high connects to U5A, pin 2;
U5D, pin 13; Q21; and Q23. Q21 and
Q23 are biased on, causing their outputs
to go low. The low from Q21 connects to
the amber Manual LED DS4 on the front
panel, biasing it on, and to Q22, biasing
it off. The drain of Q22 goes high. This
high is applied to J8-7 and will disable
any remote auto indicator that is
connected to it. Q23 is biased on and
applies a low enable to any remote
manual indicator connected to J8-6.
4.1.10.3 Automatic Control of the
Transmitter
The transmitter control board also allows
the transmitter to be turned on and off
by the presence of video or modulation
to the transmitter when the transmitter is
in Auto. When a video fault occurs due to
the loss of the video or modulation input,
J7-5 goes low. The low is applied through
W1 on J10 to Q16, which is biased off,
and to the red Video Loss Fault LED DS9
on the front panel, causing it to light. The
drain of Q16 goes high and connects to
U5B, pin 5, causing the output at pin 4 to
go low. The low connects to Q18, which
is biased off, causing the drain of Q18 to
go high. The high connects to U3D, pin
12, whose output at pin 14 goes high.
The high connects to U5C, pins 8 and 9,
which causes its output at pin 10 to go
low, and to U5A, pin 1, causing its output
at pin 3 to go low. With S2 set to
Automatic, a low is applied to U5A, pin 2,
and to U5D, pin 13. When U5A, pin 1, is
high and U5A, pin 2, is low, it causes the
output at pin 3 to go low. When U5D, pin
12, and U5D, pin 13, are both low, it
causes the output to go high. When U5A,
pin 3, is low, it biases off Q20 and
removes any pull-down to the Operate
switch. A high at U5D, pin 11, biases on
Q19 and applies a low enable to the
Standby switch; this places the
transmitter in the Standby mode.
When the video or modulation input is
returned, J7-5 goes high. The high is
applied to Q16, which is biased on, and
to the red Video Fault LED DS9, which
goes out. The output of Q16 goes low
and connects to U5B, pin 5. If there is no
receiver ALC fault, U5B, pin 6, is also
low, which causes the output at pin 4 to
go high. This high connects to Q18,
which is biased on, and causes the drain
of Q18 to go low. The low connects to
U3D, pin 12, whose output at pin 14 goes
low. The low connects to U5C, pins 8 and
9, which causes the output at pin 10 to
go high, and to U5A, pin 1. With
Auto/Manual switch S2 in Auto, a low is
applied to U5A, pin 2, and to U5D, pin