MFJ-266B HF/VHF/UHF Antenna Analyzer
Instruction Manual
2012 MFJ Enterprises, Inc.
Version 1D
13
7.2 Field Strength Measurement
The field strength function works in conjunction with the counter mode
to display Relative RF-input Level (REF FS). Any external antenna that
yields a usable signal level may be connected to the analyzer’s antenna
jack to serve as a pickup device. The usable signal range is around 30-dB
(30-mV to 1-V rms). Note that the display reading is a RMS level taken
directly from the MCU detector, so it must be multiplied by 1.414 to
obtain a peak AC value (V-rms x 1.414 = V-p, conversely V-p x .707 =
V-rms). Also, despite the display's 0.1 mV resolution, readings will be
approximations rather than precise values because of detector non-
linearity.
The Danger - High FS display warning means a dangerously strong
signal is being applied and the level should be reduced immediately.
Also, interference greater than 100 mV will almost certainly cause
inaccurate SWR measurements when in Analyzer mode.
7.3 Stimulus Generator as a Signal Source
When operated in Analyzer mode, the MFJ-266B generates a +2 dBm
CW carrier (2 mW). See section 3.6 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. Second-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 2-mW signal.
7.4 Measuring Unknown Capacitance
To measure capacitance, connect the unknown component to the
Antenna connector (usable range is from approximately 15 pF to 1200
pF). To enter the Capacitance mode, begin with the analyzer turned off,
then press and hold the Up button while pressing the PWR switch (see
Section 3.6). The screen will display the approximate value of the
unknown capacitor in pF along with the stimulus frequency where the
measurement is being made. Note that you will not have full control over
stimulus-frequency Band selection in this mode. Of the bands offered,