MFJ-225 – sign of reactance

The MFJ-225 is a recent antenna analyser from MFJ.

An important attribute of such devices is their ability or not to measure the sign of reactance.

Review of the MFJ-225 manual lists features like “Complex impedance (R and X)” which might trick buyers into thinking that it can measure X, but in fact it can only measure the magnitude of X (which is usually written as |X|), and “Phase (0-180°)” which is wrong, it measures the magnitude of Phase |Phase|.

In fairness, deep in the manual is the statement:

8.5 Sign Ambiguity (±j): Most handheld analyzers, including the MFJ-225, lack the processing capability to directly calculate the reactance sign for complex impedance (Z = Rs ±j).

A cleverly crafted statement to hide behind  a claim about “most handheld analysers” which is arguably untrue. It doesn’t matter when some or most cannot display sign of reactance, the simple fact is that if you want a handheld instrument that does correctly measure the sign of reactance, there are plenty available. The one unequivocally true part of the statement is simply:

The MFJ-225 does not display the sign of reactance or the sign of Phase.

So you might ask why then the front panel annotation is not |X| instead of X, |Z| instead of Z,  and |Phase| instead of Phase. It is misleading, either dishonestly so or just honest incompetence.

Links / references