E8257D/67D, E8663D PSG Signal Generators Service Guide 141
Troubleshooting
Overall Description
Leveling during ramp sweep (Option 007)
In ramp sweep mode, a sweep compensation reference voltage is routed from
the A9 YIG Driver assembly to the A10 ALC to improve leveling during sweep
operation. The A18 CPU controls the ALC reference correction DAC on the
A9 YIG Driver.
Analog Modulation (Option UNU Standard Pulse, UNW Fast Pulse,
UNT AM/FM and Phase Modulation)
All modulation functionality is license keyed. Without a license key entered into
the instrument, the instrument will not provide any pulse, amplitude,
frequency, or phase modulation. Two levels of pulse modulation performance
are offered. Pulse Option UNU provides pulse widths of 150 ns or greater for
frequencies at or above 3.2 GHz, 500 ns or greater for frequencies below
3.2 GHz, and with ALC off or in search mode, 1 ns or greater for frequencies at
or above 3.2 GHz, and 2 ns or greater for frequencies below 3.2 GHz with ALC
on. Pulse option UNW provides pulse widths of 20 ns or greater for all
frequencies with ALC off.
The RF can be modulated using either external or internal signals from the A11
Pulse/Analog Generator. The A11 Pulse/Analog Generator includes a pulse
generator and a numeric synthesizer that provides AM, FM, PM, and pulse
modulation capabilities. For better phase modulation control, the internal
generator is tied to the A7 Reference 10 MHz.
Internally generated signals up to 1 MHz can be switched to the LF Output
BNC on the front panel.
A11 Pulse/Analog output signals are routed as follows:
Digital Modulation
Digital I/Q modulation is generated on the A8 Lowband Vector Output and A35
3–20 GHz I/Q Modulator assemblies. The A13 I/Q Multiplexer routes the I/Q
modulation to the A8 and A35. The source of the modulation may be provided
externally via the front panel I/Q inputs or via the rear panel Wideband I/Q
(Option 015) inputs. For signal generators with Option 601 or 602, the internal
A14 Baseband Generator may be used as the source of the I/Q modulation.
The A13 I/Q Multiplexer also routes the baseband I and Q, along with their
inverses, to the rear panel.
Modulation Type Routed to
Amplitude A10 ALC
Pulse A30 Modulation Filter
A8 Output
A36 Quadraplier
A37 Upconverter
Frequency and Phase A6 Frac–N
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