64 Keysight FieldFox Handheld Analyzers Service Guide
Theory of Operation
Measurement Group
5-
SA RF Section
An external RF input signal can be analyzed when connected to the Port 2 SA
RF Input connector. Before the input signal is mixed, the signal will go through
the input attenuator and optional internal preamplifier.
The input attenuator default setting from the factory is 10 dB. The input
attenuator is used to control the amount of power at the input of the 1st
converter. Changing the input attenuator value can improve the dynamic range
of the instrument and reduce internally generated distortion products.
When the optional internal preamplifier is turned on, the displayed average
noise level of the instrument is improved. This occurs because the noise figure
of the overall system is improved. Improving the displayed average noise level
of the system enables the user to analyze low level input signals.
The 1st, 2nd and 3rd converters are used to downconvert the input signal to a
final I.F. of 33.75 MHz. That I.F. is fed to the ADC on the A5, System board. This
final I.F. on the output of the ADC can be measured at the IF Out SMB (m)
connector on the side of the instrument. Refer to “Verifying the 33.75 MHz I.F.
Output” on page 49.
The frequency bands for the SA circuitry on the RF board are listed below:
Table 5-3 Frequency Bands - SA RF Section
N991xA, N992xA, N993xA
Band Instrument
Start Stop
1 0.030 15.000
2 15.000 500.000
3 500.000 1366.250
4 1366.250 2600.000
5 2600.000 3900.000
6 3900.000 7500.000
7 7500.000 9500.000
8 9500.000 12300.000
9 12300.000 15700.000
10 15700.000 16300.000
11 16300.000 19500.000
12 19500.000 23000.000
13 23000.000 23734.000
14 23734.000 25500.000
15 25500.000 26500.000
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