Rohde & Schwarz ZPV - Page 33

The
decimal
points
stand
for a
figure
each.
For a
45°
phase
offset,
for
example,
program
PRINT (a)
26:
"PO0450"
and
for
-45°
PRINT £>26:
"PO3150".
2.5.4
Control
Amplifier
Fig.
1
shows
an
example
of
a
simple
control
amplifier
circuit.
C^,
R
x
#
R
y
>
together
with
the
deviation
of
the
FM-DC
signal,
generator,
determine
here
the
gain
and
the
time
constant
of
the
control
loop.
In
the
case
of
hi.gh-Q
crystals,
the
loop
gain
and
the
time
constant
should
preferably
be
switch-
selectable.
The
control,
amplifier
is
driven
from
the
signals
obtained
at
the
ZFV
outputs
CONTR.
AF
and
SWEEP
f
.
The
output
vol
tage
of
the
internal
phase
meter
is
available
at
the
SWEEP
output.
Scale:
0°
corresponds
to
0 V
-1.80°
corresponds
to
approx.
-0.5
V
+1.80°
corresponds
to
approx. +0.5
V.
In
addition,
a
reference
voltage
is
available
at
the
CONTR.
AF
output.
This
reference
voltage
is
proportional,
to
the
reference
value
stored
in
the
ZPV
by
means
of
the
button
f
,
1
REF
STORE
.
Scale:
0°
corresponds
to
5
V
-179*9° corresponds
to
0
V
+179.9°
corresponds
to
10 V.
If
the
two
signals
are
taken
to
an
amplifier
which
matches
the
scales
to
one
another
and
subtracts
the
signals
from
one
another,
a
voltage
is
ob-
tained at
its
output
corresponding
to
the
phase
readout
in
either
the
B/A
LIN/REF
AUTO
or
S21,S12
AUTO
mode.
If a
phase
offset
is
programmed
via
an
IEC
bus
instruction,
the
reference
voltage
at
the
CONTR.
AF
output
changes
accordingly,
e.g.
it
falls
by
1.25
V if
an
offset
of
45°
is
programmed*
R
38535
-
30