MFJ-269D Instruction Manual LF/HF/VHF/UHF SWR Analyzer
14
4.6
Frequency Counter (Function-5)
The
Frequency Counter
mode is the final Main
Mode function. To access the counter from the opening
menu, press
Mode
four times (or if already in the
Main
menu, step through it until the
Freq. Counter
screen
appears.
Important Note:
Never apply dc or more than 5 volts peak-to-peak
to the BNC
Frequency Counter
Input
jack. In this mode, the
Gate
button controls the counter's time base window. As a general rule the
longer the window, the more accurate the frequency count. The accuracy of this counter is typically
better than 0.05 %. Note that sensitivity of the counter tends to decrease with higher frequency signals.
5.0
ADVANCED OPERATION
5.1
Forward
The advanced mode provides several special functions. Some functions are very useful, such as distance
to fault (HF/VHF) or transmission line length in degrees.
Measurement Notes:
The Advanced menus present data in more "technical" or potentially unfamiliar
terms.
Advanced- 1
includes impedance descriptions such as
Magnitude and Phase of Load Impedance,
Series and Parallel Equivalent Impedance, Reflection Coefficient,
and
Resonance
. Most of these terms
are useful in special applications, such as in adjusting matching stubs, but may not be useful for making
simple antenna adjustments. The advanced menus also contain uncommon terms describing basic SWR,
such as
Return Loss
and
Match Efficiency
. These, also, represent engineering terms that may prove
misleading because "label" may not imply what is actually happening in the RF system. If a concept or
term is unfamiliar to you, it's probably wiser to avoid using it to influence your decision-making until you
understand its full technical meaning.
Information Sources:
A basic understanding of transmission line and antenna behavior and terminology
is very important in understanding Advanced Mode information provided by the MFJ-269D. Many
explanations are available in the ARRL Handbooks, and they probably suffice for most amateur
applications. Avoid unedited or self-edited amateur handbooks or articles, or at least confirm their
accuracy by checking the information against reliable professional sources. For complex questions or
critical information, we recommend using textbooks written, reviewed, and edited by professional
engineers.
Accuracy Notes:
The MFJ-269D contains a 50-ohm bridge, with voltage detectors across each bridge
leg. A twelve-bit microcontroller measures these voltages and, by applying the proper formulas, displays
useful information. The basic calculations are resistance, reactance, SWR, and complex impedance. In
some modes, the system cross checks itself and displays a weighted average of the most accurate
measurement methods, or searches for certain impedance conditions. System resolution is limited mostly
by diode linearity, calibration stability, and external noise or signals.
While we have attempted to make this unit as accurate as possible, most formulas contain squares and
other complex functions. A certain amount of error is unavoidable, especially at high or low impedance
values and especially at higher VHF or UHF frequencies.
5.2
Accessing Advanced Modes
The advanced mode is reached by pressing and holding the
Gate
and
Mode
buttons at the same time for
several seconds. After a delay of a few seconds, a series of
Advanced
messages numbered
1
through
3
appear. When you see the mode you want, quickly release the buttons. If you hold the buttons long
enough, the display will eventually loop back through the MAIN menu and repeat the cycle.