HP 54750A, User Manual, Page: 438 / 478

How the Instrument W orks
System Architecture
Probe types
There are two common types of probes suitable for use with the HP 83480A,
54750A. Each type has dierent loading eects . There is the low-impedance
resistive divider probe , like the HP 54006A, and there is the active probe ,
like the HP 54701A. A third type of probe , the compensated high resistance
passive divider probe , is designed for use with 1 M inputs and is not suitable
for use with the HP 83480-series digital communications analyzer .
Resistive divider probes Resistive divider probes are designed for analyzers with a 50 input
impedance . The tip of the probe has a 450 or 950 series resistor . The
cable is designed for a 50 transmission line . Because the cable is terminated
in 50 at the analyzer input, it looks like a purely resistive 50 load when
viewed from the tip . Therefore the resistive divider is at over a wide
range of frequencies , limited primarily by the parasitic capacitance and
inductance of the 450 or 950 resistor and the xture that holds it. The
input resistance of the probe to the circuit under test is either 500 or 1 k.
Figure 13-10. Resistive divider probe.
13-18