Wavetek 3000 Instruction Manual page 193

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 MODE switch must be 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 .
Reverse Power Protection
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 output 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 to the OFF position .
8/1B-2
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
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 POWER switch
in its OFF position, the Protection
Circuit internal 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 monitor voltage 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,
thus completing 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 .
With pin 7
grounded, the timer is
inoperative, and its output, pin 3, is
high .
The . high output from .IC202 turns
off Q213 and thus
prevents any current
flow to the front-panel UNLEVELED lamp .
If an external
RF signal exceeding 6
VRMS is applied to the instrument's
RF
OUT connector, the RF monitor voltage
at J201 will go above 5 volts . This
will produce a negative output from
IC201, and the feedback provided by
CR202 and R211 will latch IC201 in this
state . The negative output from IC201
will turn off relay driver Q201 and
cause the Protection Circuit relay to
return to
its normally
open
position, thereby removing 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 varies between 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