HP 70427A User Manual page 473

Overview
Looking at the Block
Diagram
Block Diagram
HP 70428A opt 002 Microwave Deck Assembly
HP 70428A opt 002 Microwave Deck Assembly
The HP 70428A opt 002 Microwave Source has two microwave outputs, the
microwave step reference function output generated by the HP 70428A deck
circuitry, and the frequency up-converter output. The frequency up-converter
mixes the microwave stepped reference with an external RF Source between
120 MHz and 900 MHz to produce continuous frequency coverage from 2.4
GHz to 26.5 GHz. The second YTF then selects the desired mixer sideband,
and rejects the unwanted sideband, and the LO feedthrough. The filtered
output is finally amplified to the desired output level by a second set of GaAs
amplifiers.
2.4 GHz to 25.8 GHz Microwave Stepped Reference
The 2.4 GHz to 25.8 GHz step reference output is identical to the main
output of a HP 70428A Stepped Source. The output is made available to the
front panel via a DC to 26.5 GHz SPDT switch connecting it to the step
reference output amplifier. The step reference output is necessary for
calibration of the step reference output level into the up-conversion mixer
LO port. This output has slightly lower noise than the upconverter's output,
and is available at the μW LO connector when the module is in source mode.
Microwave Upconversion Mixer
The upconversion mixer multiplies the external RF input with the stepped
microwave reference source to produce upper and lower sidebands at the RF
input frequency rate on the microwave stepped reference.
The mixer LO port is connected to the step reference output amplifier via the
SPDT, DC to 26.5 GHz switch connected to the step reference output
amplifier. The reference output level into the mixer is +10 dBm.
The mixer is operated with the IF port being used for the RF signal input. It
is specified for a frequency range of 120 MHz to 900 MHz, with an input
module level of +5 dBm. A 10 dB attenuator is added to RF input path to
protect the mixer diodes from burn-out caused by accidental DC voltage
input or electrostatic discharge (ESD).
The mixer RF port is used for the microwave signal output. It is terminated
with a 3 dB attenuator between the RF port output and the second YTF used
to select the desired mixer sideband. It is necessary to terminate the RF port
to prevent signals reflected by the YTF from causing mixer un-flatness and
mixer spurs.
13-38 HP 70427A/HP 70428A User's Guide