HP 54540 Series - Page 182

Math/FFT Menu
Vertical Scaling Units
Vertical Scaling Units
The fundamental measuring units of an oscilloscope are volts/division on the
vertical axis and time/division on the horizontal axis. This philosophy is used
for all the function operations except for FFTs. No provisions were made to
manage units for all combinations of operands and operations.
For example, if you applied a +2 V level to channel 1 and a -3 V level to
channel 2. The oscilloscope displays the product as —6 V, when in reality it is
-6V",
Making FFT Measurements
The following information will help you to make optimum measurements in
the frequency spectrum.
Connect the Dots
It is easier to view FFTs with connect the dots turned on. You can turn
connect the dots on in the Display menu.
Amplitude Measurements
For best vertical accuracy on peak measurements:
e@ Make sure the source impedance and probe attenuation is set correctly. If
the operand is a channel, the impedance and probe attenuation are set in
the channel menu.
e Set the source sensitivity so that the input signal is near full screen, but
not clipped.
e Use the flattop window.
e Set the FFT sensitivity to a sensitive range, like 2 dB/division, in the
single-screen mode or 4 dB/division in the dual-screen mode.
10-15