HP 70000 series, User Manual

Page: 415 / 447

P
in
= 10logKTB + N
o
where
P
in
is inherent average noise , in dBm
K is Boltzmann's constant, in joules
T is absolute temperature , in K
B is equivalent IF bandwidth, in Hz
N
o
is analyzer noise gure (the contribution of the active elements) in dB .
From this denition, we can see that the inherent average noise is bandwidth dependent.
Because of the power relationship above , a decade decrease in bandwidth results in
10-dB-lower noise level and consequently 10-dB-better sensitivity . When measuring
inherent average noise level, a video lter with a bandwidth much less than the IF
bandwidth should be inserted into the output circuit and the analyzer input should be
terminated with its characteristic impedance .
service-request mask
See status-byte register.
signal resolution
Ability of the analyzer to resolve two real signals present at its input. Closely spaced
signals are more dicult to resolve than widely spaced signals . Several factors , such as the
nal IF bandwidth and the shape factor , aect resolution. See resolution bandwidth and
bandwidth shape factor.
single-sweep mode
Spectrum analyzer sweeps once on demand when trigger conditions are met. Each sweep is
initiated by pressing
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
SINGLE SWEEP or executing TS or FETCH programming command.
slave
See address map.
softkeys
Keys that surround the display area.
source
Components in syntax diagram on which function operates .
span
Equals the stop frequency minus the start frequency and determines the calibration of the
horizontal axis of the spectrum analyzer .
spectrum analyzer
The spectrum analyzer presents the energy distribution of a signal as a function of
frequency . Typically , measurement results are displayed in a coordinate system where the
X and Y axis represent frequency and amplitude , respectively . The modular spectrum
analyzer , however , can operate and store measurement results without a display .
There are two types of spectrum analyzers , real-time and nonreal-time . A real-time
spectrum analyzer is tuned to the entire spectrum at once . Thus , it responds to changes in
signals as they occur . A nonreal-time analyzer , also known as a scanning analyzer , is tuned
to a single frequency at a given instant in time . So , to analyze several signals it sequentially
scans through them one at a time . Because it must wait to tune to a particular frequency , it
is not a real-time analyzer and the phenomenon under test must be repetitive or it may not
be detected. Scanning analyzers are usually the superheterodyne receiver type in which the
rst local oscillator (LO) or some IF is swept. Hewlett-P ackard modular spectrum analyzers
are superheterodyne receivers with a swept rst LO .
Glossary-16