Service manual

8 165
Theory of Operation
SOURCE THEORY
8. Theory of Operation
SOURCE THEORY
The source group generates all analog signals in the 4294A, a phase-locked test signal(fm)
to the device under test, a DC bias signal to the device under test, IF signals for the
transducer group and the vector ratio detector group, and a sampling signal for the A-D
converter on the vector ratio detector.
Figure 8-4 Source Group Simplified Block Diagram
The source group consists of the following assemblies:
• A7 Synthesizer
• A2 Hc Amp.
• A60 High Stability Frequency Reference (Option 1D5)
A7 Synthesizer
The A7 synthesizer provides the following signals:
• 240MHz signal : is supplied to the A2 and A6.
• 240MHz + fm, where fm is a test frequency of 40Hz to 110MHz: is supplied to the A2
and A6.
• fIF (230kHz/250kHz): is supplied to the A6 through the A20.
• fm+fIF: is supplied to A5 and A8.
• 4fIF (4x230kHz/4x250kHz): is supplied to the A6 through the A20.
• 4x(230-5)kHz/4x(250+5)kHz: is supplied to the A8 through the A20.