How to Use the MFJ 259D
Keith Greiner
© May 20, 2026
This page describes how to use this Smith Chart tool if you have readings from an MFJ 259 series of SWR analyzers. The MFJ 259D in this image shows the complex impedance of the load as well as both digital and analog SWR and impedance values.
The image, below shows an MFJ 259D while it is analyzing the same magnetic loop antenna as is described in the text in the section on how to use this chart tool. Here, we see a frequency of 14.040 MHz, and SWR of 1.9, and a complex impedance of R = 95 and X = 10. The total impedance is calculated using the Pythagorean theorem and is:
Z = (R^2 + Xj^2)^0.5.
In words, Z is equal to the square root of the sum of R squared plus X squared. Z = 95.52.
The impedance meter reads 100, which is about as accurate as a small meter can provide. It’s not identical to the values from the NanoVNA, but is close enough, and is a natural outcome of measurements made by one device vs. another
Figure 1. MFJ 259D.
So, the complex impedance from the MFJ 259D is R+jX = 95+j10 = 95.5.
Open the 50-ohm page on this site, and enter the frequency, resistance and reactance.
Figure 2. Selection from 50-ohm Smith Tool.
The tool returns two solutions:
Solution 1:
Beginning with the transmitter source (“Src”) on the left, then we have a series inductance of 0.544 µH and a shunt capacitor of 125.6853 pf, and then the load ( “Ld”) which is the measured complex number from the MFJ 259D. Another possible configuration is to have the inductor on the load side, but that is another solution that has other match values.
Figure 3. L-network with series inductor and shunt capacitor.
Solution 2:
Beginning with the transmitter source (“Src”) on the left, then we have a series capacitor of 236.2331 pf and a shunt inductor of 1.2743 µH, and then the load ( “Ld”) which is the measured complex number from the MFJ 259D. Another configuration is to have C1 on the load side, but that is another solution that has other match values.
Figure 4. L-network with series capacitor and shunt inductor..
The following is very important: If you compare the output from this Smith Chart tool and the above diagrams with the input fields from https://onlinesmithchart.com , remember these in this calculator are in the opposite direction compared to the online Smith Chart site. On that site, the box described as “Black Box” is the Load, and is the measured value transferred from the MFJ 259D.