A23 Lowband Coupler/Detector, A24 Highband Coupler, And A25 High Band Detector; A27 40 Ghz Doubler (Analog 40 Ghz Models And Vector 44 Ghz Models); A29 20 Ghz Doubler - Keysight Technologies E8257D Service Manual

Troubleshooting
RF Path Description (Frequency Generation, Level Control, and Modulation)
A23 Lowband Coupler/Detector, A24 Highband Coupler, and
A25 High Band Detector
The coupler couples off a portion of the RF signal which is then detected and
used to monitor the RF output power level. The detector converts the coupled
RF signal to a dc voltage that is routed to the A10 ALC, where it is compared to
a reference voltage and integrated. The integrated output provides the ALC
diode bias.
The A23 Lowband Coupler/Detector is used for frequencies ≤2 GHz; the A24
Highband Coupler and A25 Highband Detector are used for frequencies
>2 GHz.
In 20 GHz analog and vector instruments, the A24 Highband Coupler and A25
Highband Detector are located after the A30 Modulation Filter. In 40 GHz
analog models, the A24 Highband Coupler and A25 Highband Detector are
located after the A27 40 GHz Doubler. In models with output frequencies
above 40 GHz, the A24 Highband Coupler and A25 Highband Detector are
located after the A36 Quadraplier. In vector models with output frequencies
above 20 GHz, the A24 Highband Coupler and A25 Highband Detector are
located after the A37 Upconverter. The output of the A24 Coupler is routed to
either the attenuator (the attenuator is optional for the analog models and
standard for the vector models) or the RF output connector.
The A23 Lowband Coupler/Detector is located at the end of the lowband path,
prior to the A30 Modulation Filter, where the low band signal is switched into
the high band path. Because the A23 Lowband Coupler/Detector is a single
unit, the coupler and detector must be replaced together; the A24 Highband
Coupler and A25 Highband Detector are separate units that you can replace
independently.
A27 40 GHz Doubler (Analog 40 GHz Models and Vector 44 GHz
Models)
The 40 GHz Doubler generates frequencies from 20 to 40 GHz. The doubler has
two inputs from the A30 Modulation Filter. One input routes frequencies
≤20 GHz to a bypass switch, and the other input routes 10 to 20 GHz signals to
the 40 GHz Doubler. After doubling, band pass filters eliminate unwanted
harmonics. In analog models, the 40 GHz output is routed to the A24
Highband Coupler and A25 High Band Detector. In vector models, the
A27 40 GHz Doubler output is routed to the LO input of the A37 Upconverter.

A29 20 GHz Doubler

The A29 20 GHz Doubler provides RF signals to the:
— synthesis loop (described on
— low (< 3.2 GHz) band RF path (to the A6 Frac–N)
— high (> 3.2 GHz) band RF path
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page 147)
E8257D/67D, E8663D PSG Signal Generators Service Guide