BNC 835-3 User Manual - Manual (Page 14)

Sweeps
Besides the basic CW operation, the 835-3 supports several frequency and power
sweeping modes. Sweep parameters can be set in the SWEEP tab (Figure 7). Select
frequency, power or list sweep by clicking on the FREQ. SWEEP, POWER SWEEP, or
LIST SWEEP tab, respectively.
Frequency Sweep (Figure 7)
To start a frequency sweep,
a) enter start and stop frequency in Hz unit,
b) enter the number of points (or points per decade),
c) enter the dwell time in milliseconds (min. dwell time is 50 microseconds),
d) enter the off time in microseconds,
e) select the sweep mode as linear or log; additionally click “random” if random
sequence is desired.
f) select the repetition mode: enter number of repetitions or choose “infinite”
g) select the ALC mode: on, hold or off. Generally, ALC on is used. If very short
dwell times (1-2 ms) are needed, the ALC can be set to “hold”. This way the ALC
loop is disabled during the sweep. The ALC voltages are calibrated before the
sweep to maintain high level accuracy during the sweep.
h) press the on/off button.
The time resolution is 200 ns. Note that the sum of the dwell time and the off time must
be greater or equal 1.0 ms. The dwell time must be at least 50 µs, the off time can be
also be 0 (no off time). When “auto” is selected, the off time is automatically adjusted
such that during switching transients the output is disabled and the sum of dwell and off
time are at least 1.0 ms.
Under “repetition mode” you can select how many times the sweep should be executed
by entering 1 to N times, or select infinite. Selecting “Rand” will sweep the frequencies in
a random manner until terminated by user. In all cases the frequency returns to the CW
frequency as soon as the sweep is terminated.
Start and stop the sweep by pressing the ON/OFF button.
The switching transient between frequency steps depends on the step size and if internal
bands of the synthesizer are crossed. Typical switching transients are <10 µs for a
<100 MHz step (no band crossing) and <50 µs for arbitrary steps at output frequencies
>143 MHz. Transients of 100 µs can be noticed for arbitrary steps at output frequencies
<143 MHz. Transients of 400 µs occur only when switching from above 400 MHz to a
frequency below 400 MHz.
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