Operation
3-12.
Input
Attenuation.
The
input
attenuator
is
connected
between
the
RF
INPUT (.01--·18 GHz)
and
First Converter. The
attenuator
should
be
set
to
reduce
the signal level
at
the
attenuator
output
to
-10 dBm average (signal compression level). The
maximum
input
level, for each
position
of
the
attenuator
control,
for less
than
1 dB signal com-
pression,
is
indicated in red on
the
attenuator
control
dial. Unless
extra
sensitivity· is required, at
least
10
dB
of
input
attenuation
should
be
used.
This
provides a 50-ohm
termination
for
currents
at
the
IF
and LO frequencies
that
appear
at
the
mixer's
input
port.
With
the
input
attenuator
set
to
0
dB,
the
RF
INPUT is a de
block,
capable of
withstanding
± 20 volts. In
other
attenuator
posi-
tions
the
input
is a
de
return
to
ground
of
about
50-ohms and is capable
of
handling ±
400
rnA (see
CAUTION). When
in
the
0 dB
position
the
input
impedance is greater
than
50 ohms. This
may
cause
some mismatch,
VSWR. and display amplitude
variation as
the
input
frequency changes.
Care must
be
taken when
applying
de
voltage
to
the
RF
INPUT
of
the
analyzer.
Do
not
change INPUT ATTENUATION
setting while
de
is applied. Apply only
de
voltages with rise time less
than
10
6
volts
per
second and
current
with
rise
times
less
than
2 x
10
4
amperes
per
second.
Do
not
exceed
±20
volts de or
1.0
volt
ac
peaks.
3-13. Mixer Overload Characteristics.
The
input
mixer
will provide absolute calibration
at
signal
levels
up
to
-10
dBm,
incident
on
the
mixer.
Smaller signal levels will generally
be
necessary for
distortion
measurements
to
assure
that
the
meas-
urement
does
not
include
distortion
from
the
8555A
mixer. (See distortion
data
in
Table 1-2
Supplemental
Performance Characteristics.)
3-14. EXT
MIXER Connector. Provides an
output
for
the
2.05
to
3.1 GHz first LO signal. A
de
bias
voltage, adjustable from
the
front
panel, is supplied
to
the
external
mixer
through this
connector.
The
2.05
GHz
IF
signal generated
by
the
external
mixer
is applied
through
this same
connector.
The
HP
11517
A Waveguide Mixer is
recommended
as an
accessory along with Waveguide
Adapters
11518A,
11519A
and
11520A
for use over
the
12.4
to
40
GHz frequency range. Maximum
input
power
for
less
than
1 dB signal compression is typically .03
mW
peak for
the
11517
A.
To
protect
the
external
mixer
diode,
inputs
should never
exceed
1 milli-
watt.
Terminate
the
EXT MIXER
input
with
the
50-ohm
load supplied when
not
in use. When using
external mixing,
terminate
the
.01-18
GHz INPUT
with
the
50-ohm load
or
set
INPUT ATTENUA-
3-2
Model8555A
TION
to
10
or
20 dB. The
input
attenuator
is
not
in
the
external
mixing circuit,
but
does
control
the
LOG
REF
LEVEL
index
lamps. Amplitude display
accuracy will
be
approximate
with INPUT A TTEN-
UATION
set
to
match
external mixer loss.
3-15.
FIRST LO OUTPUT. A 2.05
to
4.1 GHz
output
from
the
YIG-tuned oscillator
at
a level
of
approximately
+10 dBm. Available
at
a
test
point
and
for
use
with
accessory
equipment.
Terminate
the
FIRST
LO
OUTPUT
with
the
50-ohm
load
supplied
when
not
in use.
3-16.
SECOND
LO
OUTPUT. A
1.5
GHz
output
from
second
LO
at
a
power
level
of
approximately
+9 dBm. Available as a
test
point
and
for
use with
accessory
equipment.
Can
be
used as a
test
signal
with
INPUT ATTENUATION set
to
at
least 20 dB.
Terminate
the
SECOND LO OUTPUT with
the
50-ohm load supplied when
not
in use.
3-17.
Frequency
Scales. Set
of
14
scales selected
by
the
Band Switch Lever. Harmonic
number
(n
=)
associated
with
selected scale is shown
on
left
edge
of
frequency scale.
IF
frequency (550 MHz
or
2.05
GHz being
used)
is shown
on
the
right edge
of
the
scale.
3-18.
LO
Scale. Indicates
the
fundamental fre-
quency
of
the
first LO (YIG). Cursor positioned
by
the
FREQUENCY
control
indicates
the
LO funda-
mental
center
frequency in
the
ZERO
and
PER
DIVISION SCAN WIDTH modes.
3-19. BAND
Scale. Indictes
the
frequency range
of
each
of
the
14
frequency bands. Green
dot
on
the
selected
Frequency
Scale indicates
the
fre-
quency BAND.
3-20. FREQUENCY Control. Coarse
tunes
the
analyzer's
center
frequency in
the
ZERO
and
PER
DIVISION SCAN WIDTH modes.
It
is
a two-speed
control
(push-pull action) providing
normal
or
rapid
tuning.
Do
not
use coarse
tuning
when
analyzer is stabilized (TUNING STABILIZER
ON
and
SC&.'\f
WIDTH
PER
DIVISION
set
to
blue
color-coded numbers). When stabilized, coarse
tuning will cause signal
to
jump
off
CRT screen.
3-21.
FINE TUNE. Three
turn
control
fine
tunes
the
analyzer's
center
frequency in
the
ZERO
and
PER DIVISION SCAN WIDTH modes. Use
FINE
TUNE
control
to
tune
analyzer in stabilized
mode
(see
FREQUENCY
control
above). Provides a
1 MHz
tuning
range
of
the
1st
LO (YIG)
on
fundamental mixing.
3-22.
DISPLAY UNCAL. Warning
indicator
asso-
ciated with BANDWIDTH,
SCAN WIDTH, SCAN
TIME
PER
DIVISION
and
VIDEO
FILTER
controls.
Lamp
lights when control settings are
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