RADIOBEACON TRANSMITTER
ND500II (125 WATTS) DOUBLE SIDEBAND - NO VOICE
Page 2-11
01 November 2003
reflected power on U9B-5 becomes more positive
than the reference voltage level (established by
resistors R68/R70 and
SWR THRESH
potentiometer
R69) on U9B-6, the output on U9B-7 will go high.
The output voltage level on U9B-7 will depend on the
DC level of the reflected power sample. Capacitor
C17 shapes the transient response time providing a
lower gain by connecting resistor R74 in parallel with
resistor R75 to protect against unwanted fluctuations.
The output on U9B-7 is passed to
SWR cutback
connector J3-2 and applied to a linear attenuator
circuit within the mod driver PWB. When the output
on U9B-7 is high, the input to comparator U9A's
non-inverting gate will be more positive than the
reference voltage level (approximately 0.6V
established by resistor R79 and diode CR11), on
U9A's inverting gate. The output on U9A-1 will go
high. This output is passed to four separate circuits.
One portion of U9A's output will be applied through
resistor R82 and turn on transistor Q11. A ground
control signal will be passed to the
SWR alarm
(remote)
connector J3-3 for external use. Zener
diode CR15, which provides overvolt protection
against transients, will be in-circuit (shorting jumper
E2 installed to short pins 1 and 2) when a Nautel
remote control unit is not used. CR15 will not be in-
circuit (shorting jumper E2 installed to short pins 2
and 3) when a Nautel remote control unit is used.
The output on U9A-1 is also passed through inverter
U7A and passed to diode CR14. When U7A's output
is low (SWR present), diode CR14 will be forward
biased and turn on. A low (ground) control signal will
be passed to
SWR standby
connector J3-5 and
initiates a
standby 2
keyed code indicating a SWR
condition.
The high control signal, representing a high SWR
condition, on the output of U9A-1 will also be passed
through resistor R83 and passed to the SWR alarm
lamp on the front panel. The lamp will turn on
indicating a high SWR condition exists.
A high output on U9A-1 will be applied to
comparator U3C-9, U3C's output will go high,
transistor Q6 will be forward biased and turn on.
The shutdown control circuit will be inhibited and the
subject transmitter will not shutdown when a high
SWR condition is present.
2.2.6.11
Battery Control
: The battery control
circuit is comprised of buffer amplifier U6A,
transistor Q10 and associated components. When the
subject transmitter's power source is being generated
from an AC source, the
battery status
input (J3-7)
will be low. A low will be applied through U6A to
the base of transistor Q10, causing it to be turned off.
The
battery status (remote)
output (J3-8) will be an
open collector. The battery-alarm lamp on the front
panel will be turned off. Zener diode CR10, which
provides overvolt protection against transients, will
be in-circuit (shorting jumper E1 installed to short
pins 1 and 2) when a Nautel remote control unit is
not used. CR10 will not be in-circuit (shorting
jumper E1 installed to short pins 2 and 3) when a
Nautel remote control unit is used.
If the AC power source fails, the
battery status
input
(J3-7) will switch to a high. The output on U6A-1
will go high and transistor Q10 will be forward
biased and turn on. A ground control signal will be
applied to
battery status (remote)
output (J3-8) for
external use. A high will also be applied to the base
of transistor Q3 causing it to be forward biased and
turn on. Transistor Q3 and its associated
components form a pulsing circuit which
momentarily turns on transistor Q6, through diode
CR18, to reset the shutdown circuits when AC power
is restored and the transmitter had been operating
from a DC source (battery). The shutdown circuits
will also be reset if the local
ON/OFF
switch is
toggled off and on, or a remote
on/off
command
(+15V on J4-5) is initiated.
2.2.6.12
Mod% Control
: The mod% control
circuit consists of operational amplifiers U6B/C/D
and associated components. The input on
RF voltage
sample
input (J2-6), a DC voltage proportional to the
intended
carrier level, is applied through the filtering
circuit where the RF carrier frequency will be
removed but the audio information will be passed.
The output of U6D is applied to the non-inverting
gate of U6C, and also through resistor R78 to
100%
mod ref
output (J2-4) and passed to set
100% MOD
potentiometer on the front panel. A peak detector
circuit, comprising U6C, diode CR13, resistor R81
and capacitor C18, detects the peak output on U6D-
14 and applies the DC signal through buffer U6B to
mod %
output (J3-6). When the test switch on the
front panel is set to
MOD-READ
,
the meter will be
connected between the
100% mod ref
line (J2-4) and
