Text preview for : 5991-4702EN Introduction to the FieldFox RF Analyzer - Application Note c20141027 [11].pdf part of Agilent 5991-4702EN Introduction to the FieldFox RF Analyzer - Application Note c20141027 [11] Agilent 5991-4702EN Introduction to the FieldFox RF Analyzer - Application Note c20141027 [11].pdf
Back to : 5991-4702EN Introduction | Home
Keysight Technologies
Introduction to the FieldFox RF Analyzer
University Engineering Lab Series - Lab 1
Application Note
Introduction
The Keysight Technologies, Inc. FieldFox RF analyzers are a new generation of portable,
handheld instruments which provide a variety of powerful functions all within the same
unit. They combine a precision microwave/RF swept frequency source with a tuned phase-
sensitive receiver which can be configured by embedded software to create the traditional
microwave/RF instruments such as a spectrum analyzer (SA), a network analyzer (NA),
or a cable-antenna test (CAT) system. Other functions which use the same microwave/RF
platform can also be installed as software packages, such as an RF power meter (PM), and
vector voltmeter (VVM). The FieldFox also features very high accuracy measurements with
greatly simplified calibration and a wide variety of connectivity options that allow the instru-
ment to be controlled and monitored remotely.
2
A quick overview
The Keysight N9914A is the 6.5 GHz version of the FieldFox, and its operating
range is from 30 kHz to 6.5 GHz for the CAT and VNA modes, and 9 kHz to 6.5 GHz
for the SA mode. Other models are available with frequency ranges up to 26.5
GHz. The embedded computer and controller runs a version of Windows CE, so
its boot up and shut down bears some resemblance to these systems. When the
FieldFox is first turned on, the Windows CE operating system is the first thing that
initializes. The microwave/RF source and receiver are controlled by applications
that run under this Windows CE operating system. The N9914A referenced in
this lab includes three main software applications: a cable-antenna test (CAT), a
network analyzer (NA), and a spectrum analyzer (SA). When FieldFox is first turned
on, the CAT application is normally loaded and launched first, so this is the starting
application that the user will first see upon a cold-start power up.
The front panel of the Keysight FieldFox is shown in figure 1. The power switch
is the prominent bright white button located in the lower left of the front panel.
Pressing this button once will turn on the instrument and start its boot up routine,
ultimately ending up in the CAT application. When turned on in the run mode, the
power LED below the power button will glow green. Turning the instrument off is
a little more complicated. Pressing the power button once will not turn the instru-
ment off, but instead move it into a standby mode in which the computer memory
remains loaded with its current contents, but the RF systems, display, and user I/O
are shut down to conserve power. The standby mode can be recognized by the
blank display but the power LED will flash yellow. Pressing the power button again
will move the instrument from standby to run mode, with the power LED glowing
green. The power up from standby mode is considerably faster than that from a
complete off state, since all of the operating system and applications are already
loaded into memory. To turn the instrument completely off, from the run
mode, the power button must be pressed and held down for about 5
seconds. The power LED below the power button will blink and then
extinguish to indicate that FieldFox is completely off.
The FieldFox is a battery-powered device to make it portable. The run
time depends upon how the unit is being used, but generally about
three hours can be expected from a full charge. If the FieldFox is being
used in a lab, it is generally a good idea to plug it into the DC charger
just to insure that the batteries do not run out during a lab session. The
battery pack is a four-cell Li-ion cartridge which slides into the FieldFox
through a cover slot on the lower right hand side of the instrument.
For normal use, there is no need to access the battery. The battery is
charged using the 15 Volt DC external power supply which plugs into a
standard 120 VAC receptacle. The external power supply plugs into the
FieldFox through the third rubber-sealed port from the top on the left
side of the instrument. This is located right underneath the nylon carry-
ing strap. When the battery is being charged, the power LED below the
power button will slowly pulse yellow. Complete recharging of a spent
battery usually takes about two hours. When FieldFox is running, the
display will show a battery icon at the top of the screen with a set of
bars which indicate the battery's charge status. Be aware that the bat-
tery may need to be recharged with only half of the bars still showing.
Figure 1. Front view of the Keysight FieldFox N9914A
3
The FieldFox is a two-port instrument, which means that it
has two primary connections to the device or system that
it will make measurements on. These are denoted port 1
and port 2, and shown in figure 3. The two ports get used
in different ways depending upon the application that is
running. For the CAT, the cable is connected only to port 1.
For the NA, both port 1 and port 2 are used together. For
the SA, the signal to be analyzed is
connected only to port 2.
The two ports on the FieldFox use Type-N RF connectors,
the most commonly used connector on RF instrument front
panels with frequencies of 18 GHz or less. These are rug-
ged and precision RF coaxial connectors, but their physical
size makes them somewhat awkward for use in the lab.
All of the laboratory experiments in this lab are designed to Figure 2. The FieldFox connected to its DC power supply
use the smaller and more easily handled SMA connectors.
Each of the laboratory kits for FieldFox contain coaxial adapters to convert the
Type-N (female) connectors on the FieldFox to SMA (female) connectors. As much
as these will be used, it is good practice to simply leave these adapters on the
FieldFox ports, as shown in figure 3. Instances may arise in which BNC connectors
are required to connect the FieldFox to an experiment or design project. The lab
kits also include a pair of Type-N (female) to BNC (female) adapters which can be
exchanged for the Type-N to SMA adapters when needed.
Beyond the power button, the second-most important button on the FieldFox front
panel is the Mode button located in the upper left of the keypad area. The Mode
button has a white rectangle on it to make it easier to find. The Mode button
allows selection of which software measurement application is currently running.
Pressing the Mode button assigns the installed applications to the FieldFox soft
keys, the six buttons located just below the display. The current configuration
of the FieldFox's Mode button will label the left three soft keys as CAT/ NA/SA.
Pressing one of these soft keys will launch that application. If the application has
not been loaded into memory yet, pressing one of these soft keys will load the
application and then launch it. Once an application has been loaded into memory,
launching it again from the Mode selection is quite fast.
Next in order of importance is the Measure button, also the
number "1" key on the keypad. Pressing this button brings
up a selection of pre-programmed measurement functions on
the soft keys. In some cases the right most soft key provides a
More/Back function for additional measurement functions. For
example, for the CAT application, the Measure button will bring
up the measurement functions of Distance-To-Fault (DTF) (dB),
Return Loss & DTF, Return Loss (dB), VSWR, DTF (VSWR),
Cable Loss (1-port), Insertion Loss (2-port), and DTF (Lin).
One of the measurement options will always be selected, and
that selection will appear in black background while the other
choices remain in blue background. The default wake-up state
for FieldFox is the CAT application with the Return Loss (dB)
Figure 3. Top view of the FieldFox connection ports with the SMA adapters
measurement function. attached
4
A practice cable measurement
This exercise will give some practice in setting up the FieldFox for making a cable
measurement and in the process provide some familiarization with the operation
and menu structure of the instrument.
Return loss (RL) is one of the most fundamental of RF and microwave system
measurements. Stated most simply, the instrument sends out a test signal and then
measures how much of that test signal returns. The strength of the returned signal
is expressed as a ratio relative to the strength of the original test signal which was
sent out. This makes decibels the most natural unit for expressing return loss. If 1
mW of power were sent out as a test signal, and if 0.5 mW of that test signal was
then returned, the return loss would be
Return Loss (RL) =
Preturn 0.5 mW 1