Tektronix WFM 601i, Руководство пользователя

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Measurement Applications
3–12
WFM 601i Serial Component Monitor
Measuring Error Rate
The WFM 601i features two methods of determining if a serial video system is
operating error free. The first uses the CRC check-word system documented by
SMPTE RP 165, often referred to as EDH. The second uses a fixed pattern test
signal.
The EDH system computes a CRC check-word for each field of video, and sends
this along with the video in an ancillary data field. At the EDH receiver, a CRC
is calculated for the received field of video, and compared against the transmitted
CRC. If they do not match, then one or more errors have occurred during that
field.
To measure a serial digital link, the source must insert EDH. Any serial repeaters
or processing equipment between the source and the destination receiver (where
the error measurement is being made) must pass ancillary data on the lines where
the EDH CRC is inserted. For 525 line standards this is lines 9 and 272, and for
625 line standards this is lines 5 and 318. If the source does not insert EDH, an
alternate source such as the Tektronix TSG-422 option 1S generator can be used.
This substitution is allowed because the output waveforms of sources are
standardized. The WFM 601i is connected to the regenerated serial output of the
destination receiver. See Figure 3-7.
WFM 601i
A or B Input
Channel
Serial
Source
75
Ω
Termination
Serial
Receiver
Reclocked
Serial Out
(with EDH)
Figure 3-7: Connection for point-to-point error measurements.
Check that the “EDH DET” LED is illuminated on the WFM 601i. This signifies
that EDH information is incoming. Activate the SERIAL STATUS screen. In the
middle portion of the screen, the number of program seconds that contained
errors (errored seconds) is indicated. Error information is separately tabulated for
the active picture area (AP CRC ERR SEC) and the full video field (FF CRC
ERR SEC). An elapsed time indicator gives the total time (days, hours, minutes,
seconds) since the error counter displays were last reset. This makes it possible
to calculate statistics such as percentage errored seconds. Pushing the RESET
soft key will zero both errored seconds readouts and the elapsed time counter.
Error Rate Measurement
with EDH