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3 - 54 USING THE COMBISCOPE INSTRUMENTS
PROGRAM EXAMPLE:
The following program example converts a relative or absolute FFT trace of 512
samples of 1 or 2 bytes from the signal on channel 1 via the MATH1 feature as
follows:
•
Before running this program, first make the FFT selections desired via the
front panel, such as:
> MATH - MATH1 "on" and "fft".
> CURSORS "on" and "m1.1".
> MATH - PARAM - FILTER "hamming", "hanning", or "rectang".
> MATH - PARAM - READOUT "rel" to select relative FFT.
> MATH - PARAM - READOUT "abs" to select absolute FFT.
+ CURSORS - READOUT "dBm + 50Ω", "dBm + 600Ω", "dBµV", or
"Vrms".
•
Request the following values:
> The acquisition length using the TRACe:POINts? CH1 query.
> The sweep time to calculate the MTB using the SENSe:SWEep:TIME?
query.
MTB = (sweep_time
*
50) / (acquisition_length - 1).
The calculation factor to determine the sample point frequencies is
determined as follows:
calc = 1250 / (acquisition_length
*
MTB
*
50).
> The peak-to-peak voltage to calculate the attenuation using the
SENSe:VOLTage:RANGe:PTPeak? query.
Attenuation = peak-to=peak / 8.
> The FFT type, i.e., ABSolute or RELative, using the
CALCulate:TRANsform:FREQuency:TYPE? query.
•
Read the FFT trace from memory register m1.1 using the TRACe? M1_1
query.
•
Convert and print the frequency and amplitude values of the FFT trace sample
points according to the formulas as explained before.
Note: The program prints the calculated values in groups of 20 sample
points on the screen of your computer.
Note: The program is supplied on floppy under file name EXFFTTRC.BAS.