HP 8756A How To Use

HP 5343A/5344A
SWP lNTFC A
SWP lNTFC
"T" Con nector
Figure 4. Co nnections for counting sweeper markers
usi
ng sweeper i nt erfa ce.
Suppose you analyze the display of the
HP 8756A in the LK /R measurement we have set
up, and see an anomaly in the trace. You
want to determine the frequency of the
anomaly. To use the sweeper interface
function to do this , you would follow these
instructions :
1. Connect the sweeper interface
cables as shown in figure 4 .
2 .
Make sure that the HP 53445 is not
trying to lock . Both [MANUAL L OC K)
and [AUTO LOC K) keys should be off.
3 . If you are in the NORM locking mode,
activate the sweeper interface
function by pressing [SWP M) on the
HP 5343A. This function is
activated automatically in
SUBHMNC lock . Relock the system by
pressing [ MANUAL L OCK ).
4. To activate marker 1, press [M I] on
the HP 8350B, and use the knob to
position the marker to the anomaly
on the trace . Then press [ SH IFT ]
[M2 )
on the HP 8350B to cause the
counter to count the marker instead
of the lock frequency .
The counter will count the active
marker , indicated by a blinking
light in the corresponding marker
key of the HP 8350B. The active
marker can be anyone of the five
markers , MI-M5. In the example we
activated marker one (MI) , and
moved it t o the anomaly . We can now
read the frequency of interest from
the counter . The system will stop
counting when you press [ SHIFT]
[ M3 ) on the HP 8350B . Using the
[MANU AL LOCK ) key on the HP 5344A,
unlock and then relock the source ,
and the counter will once again
display the start frequency.
QUESTIONS/ ANSWERS
Q: In LK / R, counting the sweeper' s
markers with the HP 5343A takes a long
time and the knob that adjusts the
7
A:
Q:
A:
Q:
A:
marker frequency on the HP 8350B seems
slow in responding. Is there an y thing
I can do about this?
When the HP 53445 comes to a marker
frequency, it stops the sweeper from
sweeping, and counts the frequency .
This measurement takes time . High
resolution measurements take more time
than low resolution measurements, so
the counting can be speeded up if lower
resolution is used . Use the shift key
and the blue resolution settings o n the
counter. Make sure that you are n ot
trying to lock when you enter anything
on the counter . The counter's keys
are disabled if the [ MANUAL LOC K) o r
[ AUTO LOC K) keys are active .
Why does the counter reading jump
around so much while counting marker
frequencies?
The sweeper is sweeping unlocked over a
wide band , and because of its
limitations in residual FM , resolu-
tions greater than about 100 kHz
produce unrealistically precise
counter measurements .
How can I count the stop frequency?
The HP 5344S manual says that I can
count the stop frequency by preSSing
[STOP) [SHIFT) [ M2) on the HP 8350B .
But this does not work.
Because the 8756 System Interface is
operating , this particular function
will be disabled. To count the stop
frequency set the active marker to the
same frequency as the HP 8350B stop
frequency and press [SHIFT ] [ M2 ).
SOBBARMONIC /OFFSET LOC KING
The instructions so far have detailed
operation in no r mal locking mode. This
section contains a description of
subharmonic/offset locking, its advantages
and disadvantages, and instructions on how
to use it.
The MODE switch on the rear panel of the
HP 5344A determines whether the HP 5344S will
operate in normal (NORM) or subhar-
mon i c /o ffset ( SUBHMNC ) locking. There is a
complete description of these modes in the HP
53448 Operating and Service Manual; a brief
description is provided here . In the
normal mode, the counter samples the plug-
in's RF ootput directly, and no offsets or
harmonics are used by the HP 53448. Figure 3
shows a basic transmission measurement
configuration in the normal locking mode.
Note that a power splitter or coupler is
required to sa m ple the RF output, and
external 27.8 kHz modulation is required so
that the counter samples an unmodulated
signal .
If the sweeper plug-in has a re ar panel
AUX OUTPUT (H P 83590 series and HP 86290
series RF plug - ins) , then the HP 53445
subharmonic / offset locking mode can be used
(see figure 5). In this mode the counter

HP 8756A Specifications

General

Brand	HP
Model	8756A
Category	Measuring Instruments
Language	English