User`s manual

Sweeping Arbitrary
Waveforms
When sweeping arbitrary waveforms, the start and stop frequencies
specified are start and stop sample rates. The corresponding output
frequency is the sample rate divided by the number of points in the
waveform. The following programs demonstrate how to sweep arbitrary
waveforms by specifying starting and stopping sample rates.
Sweeping Sin(x)/x and
Pseudo-Random Noise
Signals
The SWP_ARB program computes a 4096 point, 8
1
⁄
2
cycle,
phase-continuous Sin(x)/x waveform with a peak amplitude of 1V;
and a 4096 point pseudo-random noise signal.
By sweeping the Sin(x)/x signal, the different frequencies of the signal are
swept simultaneously. Starting and stopping sample rates are specified such
that Sin(x)/x is swept from 1 kHz to 2 kHz.
The noise signal is a “comb” of frequencies separated by the repetition rate
of the signal. The pseudo-random signal is repetitive. Sweeping this signal
effectively decreases the repetition rate by increasing the length of the
signal. The sampling bandwidth is 40 kHz with an effective bandwidth of
20 kHz. The output is swept from 10 Hz to 20 Hz.
BASIC Program Example (SWP_ARB)
1 !RE-STORE"SWP_ARB"
2 !This program sweeps two arbitrary waveforms: sin(x)/x and pseudo
3 !random noise. The 4096 point waveforms are swept from 4.096 MHz to
4 !8.192 MHz which results in an output frequency sweep from 1 kHz to
5 !2 kHz.
6 !
10 !Assign I/O path between the computer and E1445A.
20 ASSIGN @Afg TO 70910
30 COM @Afg
40 !
50 !Set up error checking
60 ON INTR 7 CALL Errmsg
70 ENABLE INTR 7;2
80 OUTPUT @Afg;"*CLS"
90 OUTPUT @Afg;"*SRE 32"
100 OUTPUT @Afg;"*ESE 60"
110 !
120 !Call the subprograms
130 CALL Wvfm_manage
140 !Abort the current waveform, select and initiate either the sin(x)/x
150 !(S1) or noise waveform (N1) sequence. Comment out (!) the line of
160 !the one you DO NOT want to select.
170 OUTPUT @Afg;"ABORT"
180 OUTPUT @Afg;"SOUR:FUNC:USER S1" !select waveform sequence (Sin(x))
190 OUTPUT @Afg;"SOUR:FUNC:USER N1" !select waveform sequence (Noise)
200 OUTPUT @Afg;"INIT:IMM" !wait-for-arm state
Continued on Next Page
Chapter 4 Sweeping and Frequency-Shift Keying 141