Vector-LP Radio Beacon Transmitter Technical Instruction Manual
Page
6-5
Section 6 Theory of Operation
Issue 1.1
The ac input is applied through 10 A circuit
breaker U5 and line filter U6. The ac voltage
for the RF power stage (RF power modules
A12 and A13) passes through thermistor RT1
and choke L1. Thermistor RT1 limits the
inrush current to the RF power modules.
Choke L1 improves the power factor on the
ac lines applied to the RF power modules.
The ac input is also applied to ac-dc universal
power supplies U2 and U3 (U3 optional, for
dual side transmitters), which convert the ac
voltage to low level dc voltages. The ac input
voltage is also applied to the interface PWB
(A11) for sampling by the control/monitor
stage.
Dc voltage is applied from an external 24 V or
48 V battery connected to A16TB1. The dc
voltage is fused by F1 and applied to rectifier
U8 and line filter U7 before being distributed
to dc-dc universal power supply U10 and
battery boost PWB A16A1. The battery boost
PWB boosts the dc voltage and applies it to
the RF power stage via rectifier U9.
6.3.1 Interface PWB
See Figures SD-1 and SD-21. The interface
PWB (A11) provides an interface between the
ac-dc power stage and the rest of the
transmitter. It also contains voltage regulators
(U1 and U2) that provide 9 V for the optional
modem (via E5 and E6) and 24 V (limited to
1A) for the ATU (via E3 and E4). It also
provides a dc sample of the ac input voltage
to the control/display PWB as an aid in
determining if the ac input source is at an
acceptable level.
6.3.2 Ac/Dc Universal Input Power
Supplies
See Figure SD-1. The ac/dc universal input
power supplies [U2 (side A) and U3 (side B,
if used)] are 110 W, universal ac input,
multiple dc output power supplies. The
transmitter’s ac input is applied to U2 and
U3 and the regulated 24.5 V, 15.6 V, 5.6 V
and -15.5 V supplies are provided on the
output. The outputs are applied through the
interface PWB to the remaining functional
blocks of the transmitter.
6.3.3 Battery Boost PWB (optional)
See Figures SD-1 and SD-25. The battery
boost PWB is a boost type switching power
supplies that provide a regulated B+ supply
voltage to the transmitter when a 24 V or
48 V battery is acting as the power source.
A 24 V or 48 V supply is applied to the drain
of switching FETs Q4 and Q5 through
inductors L1 and L4. The gate of FETs Q4
and Q5 is driven with square wave pulses
from pulse width modulation switching power
supply controller U4 through push-pull buffer
stage Q6/Q7. U4 is a fixed-frequency, pulse
width modulation control circuit,
incorporating the functions required for the
control of a switching power supply. The
device contains an internal sawtooth
oscillator that is set to a nominal frequency
of 100 kHz by external components R22 and
C14. The output pulse width modulated
control pulses to the gate of FETs Q4 and Q5
are generated by the comparison of this
sawtooth waveform with a feed-back voltage
sample from the output (CR6-cathode) and
the bias voltage created from the in-circuit
resistors selected by the
Battery Select 1
(J1-18) and
2
(J1-19) inputs.
The resultant variable pulse width, 100 kHz
square wave at U4-8 (
E
) is applied to the
gate of FETs Q4 and Q5 (through Q6/Q7)
and turns it on and off with the appropriate
pulses to maintain the desired set dc output
voltage.
The
Battery Select 1
and
2
inputs, applied
from the control/monitor stage, change the
level of
Battery Boost (B+)
voltage based on
the transmitter’s power level. See Table 6-1
for the logic levels.
Table 6-1:
Battery Select Logic
B+ Voltage
VR250 VR125
Battery
Select 1
Battery
Select 2
79 V
55 V
0
0
136 V
97 V
0
1
236 V
167 V
1
1
Invalid Invalid
1
0
