Agilent Technologies 4294A Specifications download pdf (Page 45)

Figure 3-8. Specifications of recommended cable (Agilent PN 8121-1218)

3-4-3. Test cable extension

If the required test cable is longer than 1 m, 2 m, or 4 m, it is possible to extend the Agilent supplied

test cable by using the following techniques.

4TP-4TP extension: As shown in Figure 3-9 (a), extension of the four coaxial cables should be connect-

ed together at the end of the extension. The actual connection is as shown in Figure 3-9 (b). An

insulated connection plate must be used in order not to break the 4TP configuration. Four BNC(f)

to BNC(f) adapters (Agilent PN 1250-0080 × 4) are used in this example. This technique can provide

the best accuracy, especially for low impedance measurement. However, in basic 4TP measurement,

its extension length is limited by the measurement frequency. F(MHz) × L(m) ≤ 15 is a typical esti-

mation for extension limitation. For higher frequency measurements and longer extension, the

shielded 2T extension technique, which is described next, should be utilized.

Shielded 2T extension: As shown in Figure 3-10 (a), the 4TP configuration is terminated and the exten-

sion cable configures a modified 3T (shielded 2T). The two outer conductors are connected together

at each end of the cable. This will cancel the magnetic field induced by the inner conductors. This

technique is used in the higher frequency region, up to 15 MHz. The residual impedance of the cable

will be directly added to the measurement result but can be insignificant error source if the DUT’s

impedance is greater than the impedance due to the residuals. For the actual connection, a connec-

tor plate (Agilent PN 16032-60001) supplied with Agilent test cable can be used as shown in Figure

3-10 (b).

Shielded 4T extension: Lower impedance can be measured accurately when the shielded 4T configura-

tion is connected as shown in Figure 3-11 (a). The actual connection is shown in Figure 3-11 (b).

Table 3-2 summarizes the extension techniques and their applicable impedance/frequency range.

3-9

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Agilent Technologies 4294A Specifications Page 45