Incorrect Sweep - HP 8340B Manual

INCORRECT SWEEP
If
the instrument sweeps, as defined above, but the YO
does not
sweep
or the frequency limits
are
incorrect,
check the
two sweep ramps from
the ASS sweep
generator assembly, 20-30 SWP (TP8) and
VSWP (TP10).
The
sensitivities
of these
lines are discussed below.
YO sweeps
widths >5 MHz are derived from VSWP. Note that the instrument sweep width, delta
F, is
related to the
YO sweep width by the harmonic
number
of the band being used. For example,
if
the
instrument
is
sweeping from
8
to
10
GHz, the
instrument
sweep width is
2
GHz. However,
this is the
second harmonic of the YO
—
the
YO
is
actually sweeping from
4
to
5 GHz;
a sweep
width of 1
GHz.
The sensitivity of VSWP
is
+2
volts/GHz of
YO sweep
width.
In the
example
above,
VSWP
should be
a ramp
starting at
zero and
going to
+2
volts.
If VSWP
is correct, look at
PRETUNE (TP3)
on the
A54 pretune/delay
compensation assembly.
It
has
a
sensitivity of
—2.5 volts/GHz of YO frequency.
In the foregoing
example where
the
YO swept from 4
to
5 GHz, PRETUNE
should go from -10 to
-12.5
volts.
If
PRETUNE
is correct, look at
SENSE (TP4)
on
the A55 YO driver assembly. This point has
a
sen¬
sitivity of about —2.34 volts/GHz of YO frequency. If
this is correct, the problem is
most likely
in the
A44 YIG
oscillator assembly.
YO sweep
widths ^5
MHz
are derived from 20-30 SWP.
The
sensitivity of 20-30 SWP
is
related to
YO
sweep width but changes depending upon
the particular
sweep
width selected, as shown
in Table
D-2.
Table D-2. Sensitivity of 20-30
SWP
Line
Sweep Width
5 MHz
^
YO sweep
width
>
500
KHz
500 KHz 2: YO
sweep
width
>
100 KHz
100 KHz
s
YO sweep width
>
10
KHz
10 KHz
^
YO sweep
width
>
1
KHz
5
KHz
^
YO sweep
width
>
500 Hz
500 Hz
2:
YO sweep width
>
100 Hz
Sensitivity
500 KHz/volt
50 KHz/volt
10
KHz/volt
1
KHz/volt
500 Hz/volt
50 Hz/volt
Verify that
VSWP
is
not
sweeping more than 0.0
to 15.0
mV and that
20-30 SWP
is
correct.
If
both of
these
are
correct, the problem
is
most likely
in the 20-30
loop.
HP 8340B/41B
Sweep Generator Assembly-Level Troubleshooting D-25