HP 8591C, Руководство пользователя, Страница: 265 / 373

Test Descriptions
Carrier-to-Noise Ratio Test Description
More about the
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Screen
The
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screen is intended to explain how the carrier-to-noise result is calculated and to
assist you in making sure this result reflects the actual carrier-to-noise on the signal being measured.
To assist you in adjusting the input level, the
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screen has several messages instructing
you to raise or lower the input level and try the test again. In addition, when conditions warrant it,
other message prompts suggesting preselection or other actions can appear on this screen. These
messages only occur when the analyzer noise-near-noise correction is correcting more than 3 The
messages are as follows:
Raise Input
This message appears when there is a need to raise the cable noise level and more input power
can be tolerated without overload.
or Reduce Input Levelxtoy
This message may appear as an alternative to raising the input level. It appears when it may be
possible to reduce the input power a small amount but just enough to cause the analyzer to switch
its internal 10 attenuator down by 1 step. This has the effect of raising the input level by
10 less the number of the input level was reduced by. Try this when raising the level is
inconvenient or impossible for some reason. Alternatively, when this message appears it signals that
it may be possible to not change the level at all, but to
the test and reduce the attenuator
manually using the keys on the 2nd C/N menu.
Preselect Input Signal:
This message appears when there is no longer any headroom to raise the level before overload
occurs, but there is still need to raise the cable noise level and there is significant channel loading
present.
Raise level10 re-entertest, turncarrieroff, reduce
attenuator:
This message appears when a preselected signal requires increased noise level but the single carrier
present will overload the analyzer. This message suggests that you raise the input level above
overload, let the analyzer measure the carrier level, then turn the carrier off to eliminate the
overload while noise is being measured.
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