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281, 282, 284
Users Manual
Alternate presses of the ± key will invert the signal at the MAIN OUT socket; if the
DC OFFSET is non-zero the signal is inverted about the same offset. The exception to
this occurs when the amplitude is specified in dBm. Since low level signals are specified
in dBm (0 dBm = 1 mW into 50 Ω = 0.224 mV rms) the - sign is interpreted as part of a
new amplitude entry and not as a command to invert the signal.
Note that for dc, sin(x)/x, pulse train, arbitrary and sequence, the amplitude can only be
displayed and entered in the Vpp form; further limitations on pulse-train, arbitrary and
sequence amplitude are discussed in the appropriate sections.
DC Offset
Pressing the OFFSET key gives the DC OFFSET screen:
DC OFFSET:
program +0.00 mVdc
(actual +0.00 mVdc)
load:hiZ
The offset can be entered directly from the keyboard in integer, floating point or
exponential format, for example 100 mV can be entered as ·1 or 100 exp -3, etc. The
display will always show the entry in the most appropriate engineering units, in this case
100mV. During a new offset entry the ± key can be used at any time to invert the offset;
alternate presses toggle the sign between + and -.
Turning the rotary control will increment or decrement the numeric value in steps
determined by the position of the edit cursor (flashing underline); the cursor is moved
with the left- and right-arrowed cursor keys. Because the dc offset can have negative
values, the rotary control can take the value below zero; although the display may
autorange to a higher resolution if a step takes the value close to zero, the increment size
is maintained correctly as the offset is stepped negative. For example, if the display
shows
program = +205· mVdc
with the cursor in the most significant digit, the rotary control will decrement the offset in
100 mV steps as follows:
program = +205· mVdc
program = +105· mVdc
program = +5·00 mVdc
program = -95·0 mVdc
program = -195· mVdc
The actual dc offset at the MAIN OUT socket is attenuated by the fixed-step output
attenuator when this is in use. Since it is not obvious when the signal is being attenuated
the actual offset is shown in brackets as a non-editable field below the programmed
value.
For example, if the amplitude is set to 2·5 V p-p the output is not attenuated by the fixed
attenuator and the actual dc offset (in brackets) is the same as that set.
The DC OFFSET display shows:
5-4
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