The headroom segment, ^n, indicates to the LA102 that a 0dB sweep may peak at
anything up to ndB. This segment is normally placed immediately before the frequency
sweep segment, and must be positioned after the test level segment (T or V). For
example, if testing a filter which has 0dB gain at 1kHz and +12dB gain at 10kHz, the
following sequence could be used:
T ^+12 U
After receiving this segment the LA102 will ignore the measured test level when
choosing the range to use. If it receives a 0dB sweep it will always choose a range
suitable for measuring ndB, where n is the segment parameter. If the sweep has a
measurement level which is not 0dB then this will be taken into account when choosing
the level. For example consider the sequence:
T ^+12 U-20
This runs a test level segment at 0dB and a frequency sweep at -20dB as well as warning
the LA102 that the system may have a gain of up to 12dB. This means that the sweep at -
20dB could peak at -8dB, so a range suitable for measuring -8dB will be chosen.
Segments with extra headroom built in (eg segment R) will still have this extra headroom.
4.26 Subtract a Reference Curve (\n)
Some measurements will always require the subtraction of a reference curve, and this can
be achieved by using the \n control segment which instructs the LA102 to subtract the
reference curve in memory n. The \n segment must appear after the frequency response
segment, otherwise the subtraction would occur before the frequency response had been
measured (the LA101 only sends this segment once, and if sending a two channel
sequence it will only send it when both frequency sweeps have been run). Some care
should be taken when using this segment to ensure that the correct reference curve is
stored in memory n before the sequence is received, and that LA102 configuration C1 is
set.
4.27 Equivalent ! Segments
Most test segments can be defined using the ! segment to generate the FSK, followed by
the necessary tones. The equivalent ! segment definitions are listed below, primarily
because this format provides a concise way of describing the tones used in each segment.
While it is possible to modify the frequencies in the ! segment, great care should be used,
because the LA102 will expect certain frequencies and levels to be used. Refer to the
relevant segment below for further details:
!A40,1000,0,100,,,315,,-.04,1000,,-.41,6300,,-6.92,10000,,-10.36
!B100,500,0,1000,,,6300,,,10000,,,
!C40,1000,0,100,,,315,,,1000,,,6300,,,10000,,
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4. User Defined Sequences
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