Agilent N5161A/62A/81A/82A/83A MXG Signal Generators Service Guide
Troubleshooting
Overall Block Description
1-7
Power Search Mode Operation
Power search mode used with modulation is similar to ALC Off mode. Using pulse modulation as an example, the difference between ALC
Off mode and power search mode is that when power search is first executed, pulse modulation is turned off, and the ALC loop is closed and
leveled. The ALC loop is then opened, pulse modulation turned on, and the integrator output is maintained at the closed loop level. Since
there is no feedback in open loop operation, power can drift over time and with temperature changes.
In power search auto mode, when changes are made in frequency or power, a new search is executed.
If ALC is on during pulse operation, pulse amplitude is maintained by the ALC loop. (See the
N5183A Data Sheet
for pulse width
restrictions.)
Attenuator Option 1E1
The ALC circuit controls power across a finite power range. The Option 1E1 attenuator, added to the RF path after the coupler/detector,
enables the ALC to maintain leveled power over an extend power range. The signal generator performs a separate calibration to remove
losses associated with the attenuator, RF connector, and cables.
Generating Frequencies
>
3.2 GHz
The A3 RF assembly provides a signal to the A7 Micro Deck’s 20 GHz doubler at a frequency range of 2.5 GHz to 5 GHz. Depending on the
desired output frequencies, the 20 GHz doubler will either pass through the > 3.2 GHz to 5 GHz frequency, double the 2.5 GHz to 5 GHz
frequency (for frequencies from 5 GHz to 10 GHz), or double the 5 GHz to 10 GHz frequency (for frequencies from 10 GHz to 20 GHz).
Instruments with Option 532 or 540 have a 40 GHz doubler that doubles the 10 GHz to 20 GHz signals.
Pulse Modulation
Pulse modulation drive for all frequencies is developed on the A3 RF assembly. For frequencies > 3.2 GHz, the pulse modulator diode is in
the Mod Filter on the A7 Micro Deck.
Amplitude Modulation
The AM drive signal is generated on the A3 RF assembly, routed to the ALC assembly on the A7 Micro Deck, and then applied to the ALC
modulation diode in the Mod Filter on the A7 Micro Deck.
A8 Floating BNC Bypass (N5183A)
The A8 Floating BNC Bypass isolation circuit is a filter that minimizes interference caused when external equipment is connected to the
external ALC Input BNC. The circuit isolates DC voltage and high frequency signal components that might be present between different
grounding paths.
A9 Interface Board (N5161A/62A)
The A9 Interface board provides voltages for the front panel LEDs and the LAN Reset hardkey. N5161A/62A front panel operation is
limited to turning the signal generator on, off and/or resetting the remote communication path.
Common Circuitry for the N5181A/82A/83A
Front Panel Hardkeys and Softkeys
Some front panel keys are referred to as hardkeys and are dedicated to specific functions. Hardkeys are used to select the most commonly
used features and to control the display's contrast and intensity.
The front panel keys along the LCD display are referred to as softkeys and are used to select functions; these functions are displayed to the
left of each softkey. When you press a softkey, its displayed functionality is executed. Some softkeys have lower-level menus that are
displayed when you press the softkey.
The front panel hardkeys and softkeys use a row and column configuration. Pressing a key makes a connection between a row and a column;
the A5 CPU interprets the data and performs the appropriate action.
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