How to determine the impedance of a high-frequency coaxial cable. Scheme, description

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How to determine the impedance of a high-frequency coaxial cable if its type is unknown. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Measuring technology

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The parameters of high-frequency cables can be determined with sufficient accuracy using an AC measuring bridge, for example, E-12-1. To do this, it is necessary to determine the capacitance of the cable segment, open at the end, then the inductance of the same segment, but closed at the end. The characteristic impedance of the cable is easy to determine by the following formula, substituting the obtained values \uXNUMXb\uXNUMXbof C and L into it:

How to determine the characteristic impedance of a high-frequency coaxial cable if its type is unknown

Measurement error does not exceed 3-5%.

To determine the cable shortening factor, measure the capacitance of a 1 m long cable section, open at the end, and substitute the resulting value into the formula:

K \u3d r (ohm) * C (f) * 10 * XNUMX⁸,

where r is the wave impedance of the cable. C is the capacity of one linear meter of the cable, open at the end.

Knowing the value of the coefficient K, it is possible to determine the resonant frequency of a cable segment of any length.

Literature

Radio No. 11, 1966, p.61

Publication: N. Bolshakov, rf.atnn.ru

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