160 E8257D/67D, E8663D PSG Signal Generators Service Guide
Troubleshooting
RF Path Description (Frequency Generation, Level Control, and Modulation)
A36 Quadraplier (Analog Models > 40 GHz)
The A36 Quadraplier is installed after the A25 20 GHz Modulator and before
the A24 High Band Detector Coupler. The A36 Quadraplier provides an input to
a through path for signals from 250 kHz to 20 GHz and an input a doubler path
for frequencies >20 GHz. The doubler path contains 2 doublers, on to
generator frequencies up to 40 GHz, and a second to generate frequencies
above 40 GHz. For frequencies > 20 GHz to ≤ 40 GHz, the doubler output is
switched to a path containing ALC and pulse modulation circuitry and then to
the A36 Quadraplier’s output. For frequencies > 40 GHz, the 20 to 40 GHz
doubler output is switched to the second doubler and another ALC and pulse
modulation control circuit before going to the A36 Quadraplier’s output.
Two prelevel detectors in the A36 Quadraplier provide feedback to the A30
Modulation Filter/ALC modulator to control the power into the A36
Quadraplier. One pre–level detector is located in the 20 GHz to 40 GHz path,
and the other is located in the > 40 GHz path. The ALC modulator drive signal
from the A10 ALC board is routed to the A36 Quadraplier to control the power
level and provide AM modulation. Depending on the frequency, the ALC
modulation drive is switched to the A30 Modulation Filter, the
A36 Quadraplier’s 20 to 40 GHz path, or the A36 Quadraplier > 40 GHz path.
A37 44 GHz Upconverter (Vector Models > 20 GHz)
The A37 Upconverter’s main function is to be a mixer and to generate
frequencies > 20 GHz. For frequencies less than 20 GHz, the A35 3–20 GHz I/Q
Modulator output is routed through the A37 Upconverter to the A30 3–20 GHz
Modulation Filter, then through the upconverter to it’s output.
For frequencies > 20 GHz, the output of the A35 3–20 GHz IQ Modulator is
routed to the A37 Upconverter and switched to the IF (IQ) input of the mixer.
The 40 GHz Doubler output is routed to the A37 Upconverter and connected to
the LO input of the mixer. The upconverter’s mixer LO frequency is always four
times the IF frequency. The desired RF output signal from the mixer will be
either the sum frequency (LO+IF) or the difference frequency (LO–IF). For
frequencies between 20 an 28.5 GHz the difference frequency is used. Without
correction the difference frequency mixing products will invert IQ, FM, and
phase modulation. For example, an increasing frequency FM mixer input signal
will produce a decreasing frequency FM mixer output signal. When operating
in the > 20 GHz and < 28.5 GHz frequency range, the PSG automatically
corrects internal and external IQ, FM, and phase modulation signals. However,
the PSG does not correct I and Q input signals from the rear panel for Option
015 (Wideband IQ) inputs. To maintain the correct phase relationships in this
frequency band, the I and Q wideband inputs at the signal generator’s rear
panel must be reversed.
Instruments with Option 015 route the rear panel wideband IQ inputs directly to
the IQ modulator. Swap the I and Q signals when using the rear panel wideband
IQ inputs at RF > 20 GHz and < 28.5 GHz.
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