Wavetek 3000 - Output Protection; Option 1 B Circuit Description

OPTION 1B
inserted as needed

by closing the
appropriate remote programming
switches . If remote CW/AM mode
selection is to be used, the instrument
front-panel MODEswitch mustbe placed
in the AM position . Closing the remote
CW/AM switch selects CW mode,

while
opening the switch selects AM mode .
The instrument MODULATION FREQ switch
may be placed in any position as
required .
ReversePowerProtection
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 frontpanel by
the flashing of the UNLEVELED light .
Once the switch is tripped, it will
latch
in the openposition and remain
open untilreset . Also, a combination
of a high mismatch, high output level
(over
.1 V) and changing frequencycan
cause the circuit breaker to trip .
After
removing the RF signal causing
the overload, the switch can be reset
by momentarilyturning the front-panel
AC POWER switch to the OFFposition .
8/1B-2
NOTE
Normal operation of the UNLEVELED
light
is
a
steady glow if the
instrument is unleveled . If
the
circuitbreaker
is
tripped while
the instrument
is unleveled, the
UNLEVELED light
will vary in
intensity instead
of flashing on
and off .
CIRCUIT DESCRIPTION
The Option
1B overall
Schematic
contained
in this section should be
used to follow the circuit description
given below .
Output Protection
With the instrument's AC POWERswitch
in its OFF position, the Protection
Circuitinternal relay, in series with
the RF
output, is in its normally open
position .
This prevents damage to the
attenuators or Output Amplifier if
reverse RF power
is
inadvertently
applied
to the
RF
OUT connector
while
instrument is not in use . As soon as
AC power is applied to the instrument,
IC201 will compare the RF monitor
voltage at J201 to a fixed reference
voltage of approximately 5 volts .

As
long as the RF monitorvoltage is less
than the 5 volt reference, the output
of IC201 will be approximately+17
volts . This positive output from IC201
turns on
the relay driver 
Q201, which
energizes the Protection Circuit relay,
thuscompleting the RF output circuit .
The positive
output
from
IC201 also
turns on
Q202 ; thus effectively
grounding pin
7 of
timer
IC202 which
operates as an
astable
oscillator
.
Withpin 7
grounded, the timer is
inoperative,
and
its output, pin 3, is
high .

The . high output from .IC202 turns
off Q213
and thus prevents anycurrent
flow
to the front-panel UNLEVELED lamp .
If
an external RF signalexceeding

6
VRMS
is applied to the instrument'sRF
OUT connector, the RF monitorvoltage
at J201 will go above 5 volts .

This
will produce a negative outputfrom
IC201, and the feedback provided by
CR202 and R211 willlatch IC201 in this
state .

Thenegative output from IC201
will turn off relay driver Q201 and
cause the Protection Circuit relay to
return to
its normally
open
position, therebyremoving the external
RF signal from the Attenuator
circuitry .
The
negative output from IC201 also
turns off
Q202, thus removing the
ground
on pin 7 of timer IC202, which
allows
the timer to operate as an
astable oscillator . The output on pin
3 of
IC202 then variesbetween 0 and +7
if an external RF voltage of
approximately 6 VRMS or more is
accidentally applied to the
instrument's RF OUT connector, an