Wavetek 3000 Instruction Manual page 202

INTRODUCTION
Option 3 is a circuit breaker in the
RF output system of the instrument . This
prevents damage to the RF output system
in the event that large RF signals are
fed into the
signal generator while
testing a transceiver . In addition to
the RF protection, the option contains
a DC block which will prevent damage to
the Attenuator if the RF output is con-
nected to a circuit operating at
a DC
potential .
SPECIFICATIONS
Frequency Range
1 to 520 MHz
Insertion Loss*
< .2 dB
VSWR**
< 1 .15
Trip Time
< 2 msec
RF Trip Level
_ .7 W
Max RF
50 W
DC Blocking Voltage
100 Volts
* This loss is calibrated out when module
is installed in the signal generator .
** The VSWR of the generator is increased
to <1 .25 when this module is installed .
OPERATING INSTRUCTIONS
If an external RF voltage of approximate-
ly 6 VRMS
or more is
accidentally ap-
plied to the instrument's RF output con-
nector, an internal switch in series with
the RF output will open .
This prevents
damage to the instrument's Attenuator
or Output Amplifier .
This open switch
will be indicated on the front panel by
the flashing of the UNLEVELED light .
Once the switch is tripped, it will
latch in the open position and remain
open until reset . Also, a combination
of a high mismatch, high qutput level
(over .1 V) and changing frequency can
cause the circuit breaker to trip .
After
removing the RF signal
causing
the overload,
the switch
can be reset
by momentarily
turning the front-panel
AC POWER switch off .
THEORY OF OPERATION
.
OPTION -3
RF OUTPUT PROTECTION
NOTE : Normal operation of,the UNLEVELED
light is a steady glow if the instrument
is unleveled . If the circuit
breaker
is tripped while the
instrument is un-
leveled, the UNLEVELED light will
vary
in intensity instead of flashing on and
off .
Figure 8/3-1 is a block diagram of the
RF circuit breaker . This block dia-
gram, along
with the M35-1 Schematic,
should be used to follow the informa-
tion contained in this section .
With the instrument's
POWER switch set
to the
OFF position, relay
Kl is in
it's normally open position .
This pre-
vents any damage to the instrument while
it is not in use .
As soon as AC power
is applied
to the instrument, ICI will
compare the voltage
from RF
monitor
CRI to a fixed reference voltage of ap-
proximately 5 V.
As long as the output
of the
monitor is less than the
5 V
reference
voltage, the output of
ICI
will be approximately +17 V .
This pos-
itive output from IM turns on the relay
driver, Q1 .
This engerizes
relay K1,
thus completing the RF output circuit .
The positive output from IC1 also turns
on Q2 .
This effectively grounds pin 7
of timer IC2,
which is being operated
as as astable oscillator .
With pin 7
grounded, the timer is inoperative, and
its output, pin 3, is high . The high out-
put from IC2 turns off Q3 . This prevents
any current flow to the
front-panel
UNLEVELED light .
If an external RF signal exceeding 6 VRMS
is applied to the instrument's RF out-
put connector, the output
from monitor
diode CR1 will go above 5 V .
This will
produce a negative output from IM The
positive feedback provided
by R7 will
latch IC1 in this state .
The negative
output from IC1
will turn off relay
driver Q1 . This causes relay K1 to re-
turn to its normally open position, re-
8/3-1