HP 8340b User Manual

Squegging
(^7
GHz)
1.
While
changing
the
instrument
output
power
level, observe
the
spurious
response on
a
spectrum
analyzer.
If
the
frequency
of
the
spur
changes
with
power
level, suspect
squegging.
Refer
to
the
3RD
Bias
adjustments
in
Section
V.
Synthesized Spurs
NOTE:
For
proper
shielding,
the
screws
on
the 20/30
and
M/N
section
covers
must
be
tight.
The
HP 8340B/41B
uses
several
internal oscillators
to
generate
the desired
output
frequency.
All
the
possible
output
frequencies
can
be
described
by
the
following
equation:
Fout
=
k1*F1
+
k2*F2
+
k3*F3
k1,
k2,
and
k3
are
integers
(positive
or
negative)
and
F1, F2,
and
F3
are
the
frequencies
of
the
internal
oscillators. Because F1,
F2,
and
F3
are
phase
locked
to
the
internal
reference
(10
MHz
standard),
they
are
related to
the
reference frequency
by:
F1
=
Ref*l1/J1
F2
=
Ref*l2/J2
F3
=
Ref*l3/J3
The
I's
and
J's
are
integers.
The
combination
of
these shows
the
relationship
of
the
output frequency
to
the
reference
frequency:
Fout
=
Ref*(k1*l1/J1
•+-
k2*l2/J2
+
k3*l3/J3
...)
The
intended
output frequency
is
the
result
of
only
one
set
of
integers
in
the
above equation.
Spurs
are
possible
at
all
other integer
choices.
These choices
are
normally
eliminated
through careful
use
of
filtering,
attention to
signal
levels,
shielding,
etc.
A
Spur Family.
A
spur
family
is
characterized
by
having
the
same
mixing
path
through
the
instru¬
ment.
For
example,
if
the
5th
harmonic
of the
M/N
VCO
is
mixing
with
the
9th
harmonic
of
the 20/30
output,
the
location
of the
spur can
be
predicted
as
the
20/30
frequency
is
changed.
More
spurs
in this
family
can
be
hypothesized,
such as
the
9th 20/30
harmonic
with
the
6th
M/N
harmonic.
The
common
thread
is
that the M/N
VCO
mixes
with
the
20/30
to
cause
a
spur.
Synthesized
spurs
normally
show up
as phase
modulations
of the
YO
frequency.
As
the
spur
fre¬
quency
is
changed
(by
changing
the
carrier
frequency),
its
amplitude
remains
constant
as
long
as
the
offset
from carrier
remains
less
than
the
YO
loop
bandwidth
(50
kHz).
Beyond
the
YO
loop
bandwidth,
the
amplitude
decreases
until
the
spur
is
gone.
Synthesized
spurs
are
called
crossing
spurs,
and
are
possible
when
the
harmonic frequencies
of
any
two
oscillators
are
equal
(5th
harmonic
of
20
MHz
=
4th
harmonic
of
25
MHz).
A
characteristic
of
crossing
spurs
is
that
the
offset
of the
spur
from
the
carrier
changes as
the
carrier
is
moved.
Because
of
this,
there is
a
frequency
at
which the
offset
must
be
zero
(assuming
the
sources
of the
spurs
can
be
tuned
to
this
frequency).
This
frequency
is
called
the
crossing frequency
of
the
spur.
The
ratio of
the
change
in
spur
offset to the
change
in
carrier
frequency
is
called the
order.
Names can
be
assigned
to
the
different
spur
families, such
as type
A,
B,
C1,
C2,
C3,
etc.
Each
of
these
have
a
set
of
defining
conditions to determine
the
crossing
frequencies.
HP 8340B/41B
Assembly-Level
Service
Overall
Instrument
Troubleshooting
A-47

HP 8340b Specifications

General

Brand	HP
Model	8340b
Category	Inverter
Language	English