Wavetek 3000 - Option 1 A Circuit Description

OPTION lA
After removing
the RF signal causing
the overlaod, the switch
canbe reset
by momentarily turning the front-panel
AC POWER switch off .
Normal operation of the UNLEVELED
lamp is
a steady glow if instru-
ment is unleveled
. If the
RF
circuit breaker is
tripped while
the instrument is
unleveled, the
UNLEVELED lamp will vary in
in-
tensity instead of flashing
on and
off .
CIRCUIT DESCRIPTION
Figure8/lA-1 is a block
diagram of RF
Level ProgrammingOption 1A .
Refer
to
this diagramand the appropriate sche-
matics in section 6 to follow the circuit
information contained in this Section .
ReversePower Protection Circuit
The ReversePower Protection circuitry
is located in the Programmable Attenautor
and in AttenuatorDrivemodule M41A-1
.
With
the instrument's AC
POWER switch
turned
off, the Protection
Circuit internal
relay, in series with the
RF output, is
in its normally open position . This
prevents damage to the Attenuator
or
Output Amplifier
if reverse power
is
inadvertently applied to the
RF OUT
connector while instrument is not in use .
As soon as AC power is applied to instru-
ment, the comparator, IC1, will compare
the RF monitor voltage to a fixed
reference
voltage of approximately 5
volts
. As
long as the monitor voltage
is less than
the
5
volt reference, the
comparator output
will be approximately
+17volts .

This positive output turns
on relay driver Q1, which energizes the
Protection Circuit relay, thus completing
the RF output circuit .
The positive outputfrom TC1 also turns
on Q2 ; thus effectivelygroundingpin 7
o£
timer IC5, whichoperates as an astable
oscillator .

Withpin 7 grounded, the
8/IA- 4
NOTE
timer is inoperative and
its output at
pin
3
is "high" . The
"high"
output
from
IC5
turns off Q3 and thus
prevents the
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 monitorvoltagewill go
above 5 volts .
This will produce a
negative output from
IC 1, andthe feedback
provided by the negative
latch diode and
resistor will latch IC1 in
this state .
The negative output from ICI
will turn
off relay driver Q1 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
fromcomparator IC1
also turns
off Q2, thus removing the
groundfrom pin 7 of
timer IC5, which
allows the timer to oscillate . The output
at pin 3 of IC5 them varies
between
0
and
+7
volts . As the output
swings down toward
0,
Q3
turns on and suppliescurrent to
the front-panel UNLEVELED lamp ;
then,
as the outputrises toward
+7
volts, Q3
turns off and prevents current flow .
This on/offcycle of Q3 causes the
UNLEVELED lamp to flash .
The comparator cam be
unlatched _by
momentarilyremoving AC
power to the
instrument after the external
RF signal
is removed .
Front-Panel RF Level Control
WhenOption lA is installed, the
RF output
level is
adjustable over a range of 110
dB (+13
dBm
to -97
dBm) as follows : The
output can be
reduced 10 dB by level
program relay K2 on Meter
Board
B005 .
The ProgrammableAttenuator
provides
another 90 dB of attenuationin 10 dB
steps, and the OUTPUT
VERNIER provides
continuousadjustment of the outputlevel
over a 10 dB range .
These combine to
provide a
total attenuation of 110 dB .