Vectronics SWR-584B - Manual (Page 13)

SWR-584B Instruction Manual HF/VHF SWR Analyzer
13
“Inductance in uH” is the third mode, and measures inductor values in microhenries (uH) at an adjustable
frequency. Normal measurement range is from less than .1 uH to a maximum of 60 uH. Inductance is calculated
using measured reactance (X) and operating frequency.
The SWR-584B becomes inaccurate measuring reactance below 7 ohms or above 650 ohms. If component
reactance is in the inaccurate range, “L(X<7) [X]” or “L(Z>650)” will be displayed. An inductance value will
not be displayed if measurement range is questionable.
To measure inductance:
1.) Turn the SWR-584B on and step the mode switch through until the “Inductance in uH” display appears.
2.) Connect the inductor across ANTENNA connector with the shortest leads possible, or with the lead length
normally used in the working circuit.
3.) Adjust to a frequency as close as possible to the working frequency, but one that does not produce a range
warning. L(Z>650) is one warning, and L(X<7) is another. L(X=0) indicates the inductor appears as a near
perfect short to the SWR-584B, and indicates frequency is too low or the inductor too small to measure.
When measuring an inductor, the displayed inductance value will sometimes change with test frequency. This
happens because of stray capacitance in the inductor, and in wires to the “ANTENNA” connector. At radio
frequencies inductance often changes with frequency, and is often different from dc or low frequency ac values.
The IMPEDANCE meter will indicate reactance (X in ohms) of the inductor.
Note: Lead length and placement, as well as inductor design, will affect inductance readings and in-
circuit performance. With increasing frequency, measured inductance usually increases. At
some frequency an inductor often becomes an “open” circuit, with infinite reactance. At others
it becomes a short.