(E4446A, E4447A, E4448A); Rf Section Description (E4446A, E4447A, E4448A) - Agilent Technologies PSA Series Service Manual

RF Section Description

(E4446A, E4447A, E4448A)

Purpose
The RF front end section converts input signals to a 3
This section contains assemblies which generate Local Oscillator (LO)
signals and assemblies which use the LO signals to mix the RF Input
and the subsequent IF signals. Assemblies in the RF section also
provide attenuation and circuit protection, gains and trigger signals,
and a path for the 50 MHz calibrator signal.
RF Block Diagram (E4448A Example)
Refer to the E4446A/E4447A/E4448A Overall Block Diagram
NOTE
throughout this procedure. The block diagram outlines instrument
settings and input power levels to obtain the measured levels in this
procedure.
The 3 Hz to 50 GHz RF input signal first enters the input attenuators,
A14 and A15. The input attenuators provide 0 to 70 dB attenuation in
2 dB steps. The A14 Attenuator contains a switch that allows the
−25 dBm, 50 MHz calibrator signal to be switched into the signal path
for amplitude calibration. The E4446A, E4447A, and E4448A do not
have a DC blocking cap in the signal path. Therefore, the first mixer
can easily be damaged if DC is present.
The attenuated input signal enters the A19 SBTX/RYTHM assembly,
where a switch at the input of the SBTX (switched Barium-tuned
filter/mixer) routes the signal through the SBTX or to the RYTHM
assembly. Switches in the SBTX and RYTHM sub-assemblies route the
input signal to one of three mixing paths:
• If the signal frequency is 26.8 GHz to 50 GHz, the signal goes
• If the signal frequency is 3 GHz to 26.8 GHz, the signal is routed
Chapter 4
through the tracking preselector and mixer in the SBTX where it is
down-converted to 3.9214 GHz and sent to the A30 First IF
Amplifier (FIFA). The output of the FIFA is connected through a
3.9214 GHz bandpass filter to the second mixer on the A20 Lowband
assembly. The second mixer converts the signal to 321.4 MHz.
through the 27 GHz low pass filter cable to the RYTHM (routing
YIG-tuned harmonic mixer) where it passes through a YIG-tuned
filter. The YIG-tuned filter tracks the displayed input signal as the
instrument sweeps and removes spurious signals such as images
and multiples. Next the signal is down-converted to the 321.4 MHz
IF using the harmonically-pumped mixer. The IF signal is then sent
to the A10 Third Converter.
Troubleshooting the RF Section (E4446A, E4447A, E4448A)

RF Section Description (E4446A, E4447A, E4448A)

rd
IF of 21.4 MHz.
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