Conversely, if the load is
large, the slave timers U1 and U2 will
Xmt RF from the power amplifier is
stay on (low) for a longer interval.
routed through the energized contacts of
relay K1 of the selected filter via the
Overload Latch. The overload
filter network and through the rf low
latch circuit Q1, Q2 will shut the slave
pass filter and the rf detector to the
timers U1 and U2 off if an abnormally
The rf low pass filter
large load should appear. The large
is an L-C filter network which improves
current flow through R3 will turn Q1 on
the high frequency suppression (above
which will then turn Q2 on, which then
30 MHz) of the selected bandpass filter.
causes Q1 to latch on.
A large voltage
The rf detector generates dc voltages
then appears on the Voltage Feedback
proportional to the forward power (VFWD)
line and turn U1 and U2 off.
and the reflected power (VREFL).
supply remains off until the +28v input
is removed momentarily by switching the
radio off and then back on:
operation is in the reverse direction:
from the antenna tuner through the rf
detector and rf low pass filter, and
through the energized contacts of the
selected filter to the power amplifier.
The power amplifier
boosts the 0.25-watt (nominal) output
from the modulator/demodulator to pro-
This module converts
vide 20 watts (nominal) rf power at the
+28v from the battery (via the control
The module also contains tem-
panel) to +6.5v and +12.5v for use by
perature compensation and overpower pro-
the other modules.
tection circuits which prevent damage
in the event of a malfunction.
tion, the regulated power supply for the
antenna tuner relays is in this module.
conversion from +28v to +12.5v/+6.5v is
performed by the down switchers U3 and
U4 shown in the detail of figure 2-11.
In transmit operation, relays K1 and
A transistor switch (Q) is driven on and
K2 are energized by the Keyline signal
off at a switching frequency of approxi-
from the modulator/demodulator. These
mately 77 kHz.
When the switch (Q) is
relays switch the amplifiers into the
closed, current flows through the
rf path in the transmit mode.
inductor (L) and charges the capacitor
cause +28v Battery to be switched into
When the switch opens, the energy
the system as +28v Battery Xmt.
stored in the inductor (L) is trans-
+28v Battery Xmt is present, switch Q13
ferred into the capacitor (C) via the
conducts and applies +6v Transmit to
The voltage on the capacitor
In receive operation,
(C) is determined by the ratio of closed
the relays are deenergized and the rf
to open time of the switch (Q). The
bypasses the amplifiers.
switch (Q) and diode (D) are integrated
parts of switching regulators U3 or U4.
RF Preamplification. The
The other elements are discrete.
driver stage (T1, Q3, Q6, T2) amplifies
the 0.25-watt Xmt RF to about 2 watts
Switching Frequency. The volt-
using a push-pull amplifier configura-
age feedback from the +12.5v or +6.5v
tion (basically two transistors Q3, Q6
output modulates the on/off periods of
with input and output transformers T1,
timers U1 and U2, respectively.
This stage is powered by +28v
is, if the load is small, the capacitor
The amplification of this
will charge easily and cut the slave