MFJ MFJ-213 - Advanced Functions; Stimulus Generator as a Signal Sourc

$i
MFJ-213
HF/VHF/UHF
Antenna
Analyzer
Instruction
Manual
isolation
between
the
feedline
and
the
antenna.
Isolation
problems
typically
occur
when
unbalanced
coax
line
is
connected
directly
to
a
balanced
element
such
as
a
dipole
or
a
loop,
and
the
outer
surface
of
the
coax
shield
literally
becomes
a part of the antenna.
If the length
of the shield
happens
to
presents
a
low
impedance
path,
it
can
load
the
element
significantly
and
shift
the
minimum-SWR
frequency
unpredictably.
It
will
also
introduce
needless
mismatch,
divert
transmitted
RF back
toward
the operating
position,
causing
RFI
problems
in
the
residence,
and
increase
unwanted
noise
pickup
in
receive
mode.
The
best
way
to
decouple
the
outer
surface
of
the
shield
from
the antenna
element
is with
a balun.
Current-type
baluns
work
best because
they
have
higher
power-handling
capability
and less loss than
other
types.
An
effective
current
balun could
be
as
simple
as
a
few
loops
of
coax
taped
together
at the feedpoint,
but for best
common-mode
rejection,
a Guanella-
style
balun
wound
on a ferrite
core
is recommended.
7.0 ADVANCED FUNCTIONS
Here are some of the MFJ-213 advance functions. Note that some of these
procedures involve connecting component leads to the unit's Antenna
connector. For these connections, we suggest making up a very short UHF-
male coaxial pigtail or obtaining a UHF dual binding post adapter to prevent
damage the center-contact of the analyzer connector.
7.1 Stimulus Generator as a Signal Source
When operated in Analyzer mode, the MFJ-213 generates a 0 dBm CW
carrier (1 mW). See section 3.1.1 for setup procedures. Output will vary
slightly, depending on frequency and operating voltage, but typically holds
to within 1-2 dB of the rated power level over the analyzer's frequency
range. Harmonic suppression averages -20 dBc. A quarter-wave stub or low-
pass filter may be installed if greater harmonic suppression is required for a
specific application. Frequency stability and carrier purity are sufficient for
testing filters, mixers, low-power amplifier stages, and for checking antenna
patterns when a range antenna is connected to the analyzer output. The
stimulus generator may also be used for producing lower-level signals with a
suitable precision RF attenuator installed in line. When connecting the
generator directly to active circuitry, always insert a coupling capacitor to
prevent DC voltages from back-feeding into the bridge circuit and destroying
the detector diodes. Also, avoid connecting the stimulus signal directly to
sensitive preamps or receiver circuits that could be damaged by an un-
attenuated 1-mW signal.
Version 1 i © 2012 MFJ Enterprises, Inc