LeCroy LW110 User Manual page 52

Using The Instrument 3-22
1. Carrier Sample Clock – This is the frequency of the sample as
displayed after you press the FREQUENCY button. Note that the
first line on the display shows Freq and some value and the second
line shows Sclk and value. This Sclk is what you need to interpret
your carrier frequency. This is also the frequency that is available
as sine waveform at the rear-panel sine output. If you do not care to
work with your sine output but want to generate FM from the front
panel, then you must define your carrier frequency first. Here is
what you do:
When generating standard waveforms, your sample clock
frequency is computed automatically. In fact, when you program
your waveform
automatically. You cannot access or modify the sample clock
field, it is there for reference only. Although you cannot change
the sample clock, this is the value you'll be using for the FM
carrier.
It is a bit simpler when you generate arbitrary waveforms. The
only value that you see on the display is Sclk and this is the
value of your carrier frequency. It is also the frequency of the
sine waveform at the rear-panel sine output connector. However,
if you want to know the frequency of your signal at the front
panel outputs, then you must computed it yourself from the sclk
frequency, divided by the number of points in your active
segment. For example, if your sclk is 100 MS/s and you have a
1000-points waveform, then your output frequency is 100 KHz.
2. Deviation Range – This parameter specifies the range of which
the sample clock frequency will deviate from the carrier frequency
setting. The deviation range is symmetrical about the carrier
frequency. As was mentioned before, the LW120 has an extremely
wide deviation range, without scarifying linearity. For example you
can set 25 MS/s carrier with 40 MS/s deviation, that is, your carrier
frequency will swing from 5 MS/s to 45 MS/s.
3. Modulating Waveform – Defines the shape and type of the
modulating waveform. You can modulate the carrier with internal
waveforms only. In other words, you cannot apply your own
modulating carrier to an external input. The LW120 has a library of
waveforms built into the software that allows selection of standard
waveforms, such as, sine, triangle, square and ramp. As explained
above, this mode is called "Standard FM Mode" You can also
generate your own modulating waveform but, for this purpose, you
must use external application such as ArbExplorer. Again, this
mode is called "Arbitrary FM Mode".
4. Modulating Frequency – Defines the rate of the modulating
frequency. If you use the standard FM mode, the maximum
modulating frequency is 100 KHz. Using the arbitrary FM mode, the
maximum envelope frequency is increased to 200 KHz.
frequency, the Sclk
User Manual LW120
value is updated