Fluke 271 manual FSK Mode, Special Waveforms, Staircases, TGEN=250.ms 4.000 Hz, Getting Started

Getting Started

Using the Instrument

FSK Mode

The FSK (frequency shift keying) mode can also be driven from the internal trigger generator. Setting up is very straightforward; the following settings give a continuous waveform which switches between 800 Hz and 1.2 kHz twice every second.

The edit menu for the FSK mode includes the basic settings for the trigger generator, so there is no need to visit the trigger generator set-up screen itself. First, free the internal trigger generator. This is most easily done by returning to the factory default settings.

Press EDIT then FSK and enter the settings shown here:

FREQ A=800.0000 Hz

FREQ B=1.200000kHz

SOURCE=TGEN [FREE]

TGEN=250.ms 4.000 Hz

Then press FSK again to start the generator with the new settings and turn the output on.

Special Waveforms

Staircases

The instrument can generate a staircase waveform with up to 16 steps. To demonstrate the set-up process we will create a signal that approximates a 625-line PAL TV line signal. This is the signal applied to the Z-axis of the TV's CRT to modulate the brightness of the spot.

The refresh rate in PAL TV is 25 Hz (40 ms), and the screen is rasterized into 625 lines. Thus each line takes 64 µs and the line frequency is the inverse of this, 15.625 kHz.

By definition, the black level (called the "blanking level" because it cuts off the electron beam completely) is 30 % of peak amplitude and the white level is 100 %. These levels usually correspond to +0.3 V and 1.0 V respectively.

The line sync pulse is negative-going and takes the level down to 0 %. It is nominally 4.7 µs wide and it occurs in the first few microseconds of the cycle, just before a region called the "back porch" which precedes the scan.

The horizontal scan runs from 12.05 to 63.70 µs; outside this period the CRT is blanked.

To produce an image on the TV screen we will divide the scan period into five approximately equal segments and

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