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Troubleshooting
RF Path Description (Frequency Generation, Level Control, and Modulation)
A30 Modulation Filter
Because one function of the A30 Modulation Filter is to switch the highband and lowband frequency
paths to a common path, the output frequency range of the A30 Modulation Filter is 100 kHz to
20 GHz. For frequencies >3.2 GHz, the A30 Modulation Filter provides amplitude and pulse
modulation circuitry, power level control, and filtering. Frequencies <3.2 GHz are simply switched
through the A30 Modulation Filter, and are not filtered or modulated.
The highband ALC diode provides level control and amplitude modulation. With no bias applied to
the ALC diode, output power is at maximum power level. In pulse operation, the pulse diode must
be biased on for the RF signal to pass through. When the A11 Pulse/Analog Modulation Generator
is not installed:
•If the instrument does have modulation capabilities, the pulse diode is turned off and there is no
RF output.
• If the instrument does not have modulation capabilities, circuitry on the A30 Modulation Filter
biases the pulse diode on.
In 20 GHz signal generators, the A30 Modulation Filter output is routed to the A24 Highband
Coupler and A25 Highband Detector. In 40 GHz instruments, two outputs from the A30 Modulation
Filter are routed to the A27 40 GHz Doubler, as follows:
• One output routes frequencies ≤20 GHz to a bypass switch.
• One output routes 10 to 20 GHz frequencies to the 40 GHz Doubler circuit.
A27 40 GHz Doubler (Analog Models Only)
The 40 GHz Doubler generates frequencies >20 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. The 40 GHz output is routed to the A24 Highband Coupler and
A25 High Band Detector.
A23 Lowband Coupler/Detector, A24 Highband Coupler, and
A25 High Band Detector
The coupler couples off a portion of the RF signal so it can be 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 digital instruments, the A24 Highband Coupler and A25 Highband Detector
are located after the A30 Modulation Filter; in the 40 GHz analog model, they are located after the
A27 40 GHz Doubler. The output of the A24 Coupler is routed to either the optional attenuator or
the RF output connector.
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.
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