Keysight NFA Series Noise Figure Analyzers Service Guide 203
RF Section Troubleshooting (N8976B)
RF Section Description
A9 Input Attenuator A
This assembly has two 2 dB attenuator sections, a 6 dB attenuator section, and
a cal signal input port.
A10 Input Attenuator B
This assembly has a total of 60 dB of attenuation to control the signal level into
the Low Band Switch assembly. There is a 10 dB, 20 dB, and 30 dB section in
the A10 assembly. Total input attenuation with the A9 and the A10 combined is
60 dB in 2 dB steps).
A11 Low Band Switch
This assembly operates across the entire frequency range of the analyzer. The
switch has 3 main functions:
— Switch RF input frequencies from 3 Hz to 3.59 GHz RF Output to A13 RF
Front End Assembly.
— Switch input frequencies from 3.6 GHz to 44 GHz Millimeter-Wave RF
Output to A12, YTF Preselector.
— Contains standard optional high band preamplifier, which has a typical gain
of 35 dB to 40 dB and a noise figure from 9 to 23 dB up to 44 GHz.
A12 YTF Preselector
The YTF Preselector is used for input frequencies greater than 3.6 GHz. Signals
less than 3.6 GHz bypass the YTF assembly and are routed to the low band
input of the A13 RF Front End Assembly. The YTF Preselector is a YIG tunable
bandpass filter whose main purpose is to track the input signal and to filter out
unwanted spurious or image response signals. The YTF Preselector has a 3 dB
bandwidth greater than 40 MHz and an insertion loss of ~ 6.5 dB.
The preselector requires centering for optimum amplitude accuracy. The Auto
Align routine will perform a rough centering during the preselector two point
tuning algorithm. However, when troubleshooting, press Amplitude, Signal
Path, Presel Adjust to manually center the preselector.
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