MFJ-259 Instruction Manual
HF/VHF SWR Analyzer
5
Resistance Meter
The resistance meter section of the MFJ-259 will provide resistance readings for the load
connected to the ANTENNA jack. The resistance meter will not give an accurate reading of a
reactive load. For example, if an antenna is resonant at 7.1 MHz and you attempt to measure
the resistance at 7.3 MHz, the resistance reading will not be accurate. To get an accurate
reading the TUNE knob should be adjusted until the lowest SWR reading is obtained. The
point of lowest SWR is generally the point of lowest reactance therefore the most accurate
point to read the antenna's pure resistance.
If the resistance meter indicates 50 ohms but the SWR meter indicates a high SWR the load is
probably reactive. Any time the resistance meter indicates a resistive ratio that disagrees with
the SWR reading the load is reactive. For example: If the resistance meter indicates 25 ohms (
a 2:1 SWR ) but the SWR meter indicates greater than 2:1, the load is reactive.
For the SWR
to be 1:1, the load must be 50 ohms of pure resistance.
The SWR can not be 1:1 if reactance is present or the resistive component is not 50 ohms. If
the SWR meter indicates 1:1 but the resistance meter reads other than 50 ohms you are
experiencing an instrument error.
Frequency Counter
The frequency counter in the MFJ-259 will typically measure frequencies between a few hertz
and 200 MHz. At frequencies above 1 MHz, the frequency counter is sensitive to 600 mV.
Below 1 MHz, the counter is sensitive to TTL input voltage levels (5V peak to peak) with a
square wave input. The counter function is accurate to 1 part per million at room temperature.
WARNING:
The frequency counter has a CMOS input device that can be easily damaged.
To avoid damage to the counter while using the "FREQUENCY COUNTER
INPUT" jack the user must observe the following precautions:
NEVER
exceed 5 volts peak input.
NEVER
apply an input signal with the power
switch off.
To use the frequency counter turn the power "ON" and press the "INPUT" button on the top
panel until a "B" appears in the upper right corner of the counter display. The BNC jack is
now selected for input to the counter.
A basic operational check of the Channel B input on the counter can be made with a short
jumper wire. If a short jumper is placed from the center of the SO-239 connector to the center
of the BNC connector, the output of the MFJ-259 oscillator will be displayed on the counter
readout. The frequency displayed will be the same on both Channel A and Channel B, while
the jumper is in place. This check is useful when a reliable external RF source is not
available.
Input to Channel B may be provided in many different ways. The most common usage is
measuring the transmitter frequency.
Never transmit directly into the MFJ-259, or it may be