Vectronics SWR-584C User Manual download pdf (Page 26)

SWR-584C Instruction Manual HF/VHF/220MHz SWR Analyzer

• Voltage at the center of the resonance becomes high, causing severe arcing.

• Current in the windings becomes very high, resulting in severe heating.

To test for self-resonance:

[ ] Install and test the choke in its normal operating location to incorporate stray capacitance.

[ ] Disconnect any choke leads leading to associated circuitry.

[ ] Connect the analyzer to both ends of the choke using a short 50-Ohm jumper.

[ ] Set the analyzer for its default

R&X function in the Basic menu.

[ ] Tune the

VFO to slowly sweep the choke's target operating range (specific band, etc).

[ ] Looking for impedance dips. These identify series-resonant frequencies.

When a low-impedance dip is detected, move a small insulated screwdriver blade along the

choke windings to find a point where the series-resonate impedance changes suddenly. This

jump identifies the location where the voltage peaks, and it's the spot where adding or

subtracting even a tiny amount of capacitance will have the greatest effect. To shift the

resonance off the critical frequency (or out of the band), try removing turns to reduce

capacitance -- or add a capacitive stub. Note that even a small change in capacitance has a

much more impact than making a small change in inductance because the L to C ratio is very

high.

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Vectronics SWR-584C User Manual Page 26