138 E8257D/67D, E8663D PSG Signal Generators Service Guide
Troubleshooting
Overall Description
In 20 GHz vector models, the output of the A30 Modulation Filter is routed to
the A24 Highband Coupler and A25 Highband Detector, then through the AT1
attenuator to the front panel RF output connector.
In 32 and 44 GHz models, the A35 3–20 GHz I/Q Modulator routes two signals.
One signal goes to the A27 40 GHz Doubler. The second signal goes to the IQ
input of the A37 Upconverter. The output of the 40 GHz Doubler is then routed
to the LO side of the A37 Upconverter.
Lowband Path – Frequencies Below 3.2 GHz
For frequencies below 3.2 GHz, the YIG oscillator output is tuned between 4
and 8 GHz. In analog models and 20 GHz vector models, the YIG oscillator
output is routed to the A29 20 GHz Doubler microcircuit, where a portion of the
signal is coupled off and routed to the A6 Frac–N. In vector models with output
frequencies > 20 GHz, the A39 Coupler is added at the YIG oscillator output to
couple the signal to the A6 Frac–N. A divider on the A6 Frac–N divides the 4 to
8 GHz signal to a frequency between 250 MHz and 3.2 GHz. This signal is then
routed to the A8 Output assembly where it is amplified, filtered and modulated.
Frequencies below 250 MHz are generated on the A8 Output by mixing the
output signal from the A6 Frac–N (between 1000 and 750 MHz) with a 1 GHz
LO from the A7 Reference. In vector models, the A8 Output also contains the
I/Q modulation circuit.
Option UNW (improved pulse performance below 3.2 GHz) adds a fast pulse
modulator after the A8 Output. Option 1EH (reduced harmonics below
3.2 GHz) adds a filter assembly (A38 Low Band Switch Filter) after the
A8 Output. If Option UNW is installed, 1EH is installed after the A8 Output and
before the UNW assembly.
The 100 kHz to 3.2 GHz signal is routed to the A23 Lowband Coupler/Detector,
and then switched into the highband path by a switch in the A30 Modulation
Filter microcircuit. From this point, the low frequency signals flow to the front
panel through the highband path.
The A43 Amp Filter assembly is added to the low band RF path. The RF signal
flow goes from the A8 Output board into the A43 Amp Filter and then into the
A23 Low Band Coupler. The A43 Amp Filter induces the circuitry for Options
UNU and UNW for frequencies from 250 MHz to 3.2 GHz, Option 1EH, Option
007, Option 1EU, and a divider circuitry used with Option UNX.
The following paragraphs apply to E8257D instruments without Option 1EU, with
serial prefixes < US4928/MY4928/SG4928, and all E8267D & E8663B instruments.
The following paragraph applies to E8257D instruments with Option 1EU and all
E8663D instruments.
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