Agilent Technologies 85032B/E 50 Specifiche Pagina 178

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Troubleshooting and Block Diagrams 8712ET/ES and 8714ET/ES
Category 3 Failures: Inaccurate (but reasonably functional) Measurements RF Network Analyzers
4-36 Service Guide
Checking the Switch Terminations
1. Remove the load and connect a a high quality thru cable between PORT 1 and PORT 2.
2. If the max point of the S22 trace is above 12 dB, there is a port match problem in the
PORT 1 path. The most likely cause is a defective load in the switch. Replace the switch
(refer to “Removing the Switch (ES Analyzers)” on page 3-16). If the problem persists,
replace the A coupler. (Refer to “Removing the Coupler” on page 3-15.)
3. To check PORT 2, press .
4. If the max point of the trace is above 12 dB, there is a port match problem in the
PORT 2 path. The most likely cause is a defective load in the switch. Replace the switch
(refer to “Removing the Switch (ES Analyzers)” on page 3-16). If the problem persists,
replace the B coupler. (Refer to “Removing the Coupler” on page 3-15.)
Additional Troubleshooting Tips
If data is okay with just a through cable connected (after preset), but bad in an application,
check for the following:
Verify that you are looking at the expected measurement; especially check:
data vs. memory or data/memory display
channel 1 vs. channel 2 data trace
channel 1 vs. channel 2 y-axis labels (when both channels are on)
“Rel” vs. “Abs” y-axis scale
system bandwidth
narrowband vs. broadband mode
If testing long cables, slow the sweep time down until no changes are seen.
Make sure the span is not too narrow. This may cause interpolation errors with the default
or full-band calibrations. Perform a user-defined calibration at the desired frequency
range.
Mismatch errors can cause inaccuracies up to a few tenths of a dB. This is usually
noticeable as ripple in a low-loss transmission display, and is typically more noticeable in
an 8712ET/ES than in an 8714ET/ES. Excessive ripple can indicate poor source or input
match. Measure the match using the performance tests. If OK, try using an attenuator or
making an enhanced response calibration to improve match.
MEAS 1
S11 Refl Port 1
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