Keysight NFA Series Noise Figure Analyzers Service Guide 137
RF Section Troubleshooting (N8973B, 74B, 75B Analyzers)
RF Section Description
3. RF input frequencies from 13.6 GHz to 26.5 GHz go through high band
path #2. Refer to Chapter 12, “Block Diagrams” for details.
This signal level can be optimized by either Input Attenuator A or Input
Attenuator B. The signal is then routed to the low band switch, which will
route the signal to the A12 YTF Preselector.
The low band switch is biased by the A15 Front End Control Assembly. The
signal then routes to the A12 YTF Preselector before going to the A13 RF
Front End Assembly. The input switch in the RF Front End Assembly routes
the RF input signal to Mixer #3. The RF input signal is then mixed with the
1st L.O. from the A14 L.O. Synthesizer Assembly in Mixer #3 to a 1st
intermediate frequency of 322.5 MHz. The LO is doubled at tuned
frequencies above 17 GHz. The 322.5 MHz I.F. output is at A13J7 of the RF
Front End Assembly. This is the signal path for N8975B, 26.5 GHz
Frequency Range (for frequencies ≥13.6 GHz). The control voltages and
biasing for these assemblies come from the A15 Front End Control
Assembly.
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