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156 Chapter 4
Making Measurements
Using Baseband I/Q Inputs (Option B7C)
Selecting Input Probes for Baseband Measurements
The selection of baseband measurement probe(s) and measurement
method is primarily dependent on the location of the measurement
point in the circuit. The probe must sample voltages without imposing
an inappropriate load on the circuit.
The following four measurement methods may be used with baseband
I/Q inputs:
•
50 Ω Unbalanced - This is the measurement method of choice if single
ended or unbalanced baseband I and/or Q signals are available in
50
Ω coaxial transmission lines and are terminated in a coaxial
connectors. Adapters necessary to convert to a 50
Ω BNC male
connector must be of 50
Ω impedance. The methods are as follows:
— I only measurement using one single-ended probe connected to
the I input connector
— Q only measurement using one single-ended probe connected to
the Q input connector
— I/Q measurement using two single-ended probes connected to the
I and Q input connectors
•
600 Ω Balanced - This is the measurement method of choice if
balanced baseband signals having a 600
Ω impedance are available.
The methods are as follows:
— I only measurement using one differential probe or two
single-ended probes connected to the I and I inputs
— Q only measurement using one differential probe or two
single-ended probes connected to the Q and Q inputs
— I/Q measurement using two differential probes or four
single-ended probes connected to the I, Q, I, and Q input
connectors