HP 436A - Page 78

~·
Model 436A
Adjustments
ADJUSTMENTS
5-22.
POWER
REFERENCE
OSCILLATOR
LEVEL
ADJUSTMENT
(cont'd)
NOTE
Ensure that the
DVM
input
leads are isolated from chassis
ground when performing the
next
step.
7.
Set
up
the
DVM
to
measure microvolts and
connect
the
positive and negative inputs
leads, respectively,
to
the
V
COMP
and
V
RF
connectors
on
the
rear panel
of
the
432A.
8. Observe
the
indication
on
the
DVM.
If
less
than
400
microvolts, proceed to
the
next
step.
If
400
microvolts
or
greater, press and hold
the
432A
FINE
ZERO
switch and
adjust
the
COARSE ZERO
control so
that
the
DVM
indicates
200
microvolts
or
less.
Then release
the
FINE
ZERO
switch
and
proceed
to
the
next
step.
9.
10.
11.
12.
13.
Round
off
the
DVM
indication
to
the
nearest microvolt
and
record this
value
as
V
0
.
Disconnect the
DVM
negative
input
lead from the
VRF
connector
on
the
432A and
reconnect
it
to
chassis ground.
Set
the
Power Meter
POWER
REF
switch
to
ON
(in)
and
record the indication
ob-
served on the DVM
as
V COMP
.
Disconnect the
DVM
negative
input
lead from chassis ground
and
reconnect
it
to
the
V
RF
connector
on
the
rear panel
of
the
432A. The DVM
is
not
set up
to
measure
V
1
which represents
the
power reference oscillator
output
level.
Calculate the value
of
V
1
equal
to
1 milliwatt from
the
following equation:
v
1 -
v
0
=
v
COMP
-J
(VCOMP
)
2
-
(10"
3
)
(
4R) (EFFECTIVE EFFICIENCY)
where:
V
0
=
previously recorded value
V
COMP
=
previously recorded value
10·
3
=
1 milliwatt
R
=
prev.iously recorded value
EFFECTIVE EFFICIENCY
=
value
for
thermistor
mount
at
50
MHz (traceable
to
the
National Bureau
of
Standards).
14. Remove the Power Meter
top
cover and adjust LEVEL
ADJUST
potentiometer
A8R4 so
that
the
DVM indicates
the
calculated value
of
V
1
.
5-11