Tektronix WFM 601i, User Manual

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Installation
WFM 601i Serial Component Monitor
1–15
WFM 601i
Serial
Router
Serial Video
Output Signal
Serial
Sources
Normal
Through
Patch Panel
Figure 1-9: Monitoring serial digital signals around a routing switcher.
The WFM 601i uses passive loop-through serial inputs, similar in concept to
those commonly found in baseband video equipment. Accordingly, the
loop-through must be terminated externally. It is important that this external
termination meet accuracy and return loss requirements.
If the instrument is installed to monitor an operating link, with the serial source
on one side of the loop-through and the destination receiver on the other side, the
destination receiver (and the cable between it and the loop-through) serves as the
termination. This is the preferred monitoring connection because the
performance of the entire serial path can be inspected. The return loss of the
WFM 601i is sufficiently high that, in most cases, the system return loss will be
set by that of the destination receiver.
In cases where the WFM 601i is placed at the end of a link, a bnc termination
must be installed on the other side of the loop-through. This connection might be
used to measure a source, for example. The termination must be 75
, and its
return loss should exceed 25 dB from 10 kHz to 270 MHz. It is preferable that it
be dc coupled (good return loss extends to dc). The terminators supplied with the
WFM 601i (P/N 011–0163–00) are recommended. Be aware that good return
loss at baseband video frequencies (dc to 6 MHz) does not guarantee good high
frequency return loss.
Line Termination