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TM
11-5820-919-40-1
Conversely,  if  the  load  is
timer  off.
Transmit/Receive
RF
Processing.
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
antenna  tuner.
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.
The  power
and  the  reflected  power  (VREFL).
supply  remains  off  until  the  +28v  input
is  removed  momentarily  by  switching  the
Receive
Operation.
Receive
radio off and then back on:
operation  is  in  the  reverse  direction:
from  the  antenna  tuner  through  the  rf
AMPLIFIER/COUPLER
UNIT.
detector  and  rf  low  pass  filter,  and
through  the  energized  contacts  of  the
POWER
AMPLIFIER
selected  filter  to  the  power  amplifier.
General.
The  power  amplifier
POWER
SUPPLY
boosts  the  0.25-watt  (nominal)  output
from  the  modulator/demodulator  to  pro-
General.
This  module  converts
vide 20 watts (nominal) rf power at the
+28v  from  the  battery  (via  the  control
The  module  also  contains  tem-
antenna.
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.
In addi-
tion, the  regulated  power  supply  for  the
Down  Switching.
The  actual
antenna  tuner  relays  is  in  this  module.
conversion  from  +28v  to  +12.5v/+6.5v  is
performed  by  the  down  switchers  U3  and
Transmit/Receive
Operation.
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.
They  also
inductor  (L)  and  charges  the  capacitor
cause  +28v  Battery  to  be  switched  into
When  the  switch  opens,  the  energy
(c).
the system as +28v Battery Xmt.
When
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
diode  (D).
In  receive  operation,
various  circuits.
(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.
That
This  stage  is  powered  by  +28v
T2).
is, if the load is small, the capacitor
Battery.
The  amplification  of  this
will  charge  easily  and  cut  the  slave


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