Large MFJ SWR/Wattmeters
This article is for vision-impaired amateur radio operators interested in high visibility MFJ SWR/Wattmeters—Models 867, 868, and 869. All three models have the same large analog meter design for visibility.
Model 868 tested for this review has a frequency range of 1.8 - 30 MHz. Model 869 has an extended range to 60 MHz and additional features. Model 867 covers VHF/UHF frequencies.
Size and Visibility
The case of the MFJ-868 measures 7.3"W x 6.5"H x 5.5"D. The large meter (Figure 1) has a single red needle. The part of the meter shown in the Figure measures 5.7"W x 3.0"H.
Figure 1. Large meter on the MFJ-868.
Three separate nonlinear power scales are for 20, 200, and 2000 watts full scale. The numerals are high contrast, 0.15" high for the 2 kW scale and 0.12" for the other two.
The nonlinear SWR scale has red numerals that are 0.12" high, and the scale above 3.0 is bright red.
The labels for the controls on the instrument are white letters on black, measuring 0.1" high.
Three of the controls are black buttons. Viewed against the black case, it may be hard to see whether they are IN or OUT, but they are large enough (0.3" diameter) to feel the difference.
A 9 volt battery or an external 12 volt power supply (not included) can be used. To conserve power the meter circuit turns off until RF is sensed. With battery power the two small backlights remain off.
RF Power Measurement
A switch on the Model 868 selects peak or average power, and another selects the forward or reflected direction.
The single needle design may be easier to read than more common cross-needle meters. A calibration step is necessary before measuring SWR: With the RF power source on and the SWR/Set button in the "Set" position, adjust the knob on the front panel for full scale needle deflection. The setting depends on the RF power level. With the button in the "SWR" position, the needle indicates the SWR.
The manual states that the meter has been calibrated at the factory, but it does not specify the accuracy.
A QST reviewer estimated the accuracy at about plus or minus 5% at full scale, compared to a Bird wattmeter. According to the manual the most accurate power readings are in the upper half of each meter scale.
A recalibration procedure requiring a standard reference source and a 50-Ohm dummy load is described in the manual.
The large SWR/Wattmeters by MFJ have high-visibility meter scales.
Peter DeNeef, AE7PD, is an Extra Class amateur radio operator in the U.S. This web site has no ads or conflicts of interest.
Email: HamRadioAndVision "at" gmail "dot" com.