Models LB480A/LB680A
USB Powe™
Product Manual PPA (Pulse Profiling Application)
Revision: 08/02/11
47
Filter
The
Filter
drop down allows you to select an appropriate video bandwidth depending on your measurement needs.
The default value is 10 MHz if you have option 004. If you do not have option 004 then the default (and only value) is
100 kHz. (Filter selection: 100 kHz, 200 kHz, 300 kHz, 500 kHz, 1 MHz, 2 MHz, 3 MHz, 5 MHz, 10 MHz).
Both averaging and filtering help reduce the noise floor. Below about -53 dBm you may need to use a combination of
averaging, filtering (Option 004), and the standard external triggering capability to get satisfactory measurements.
External triggering has the advantage of triggering on demand and is not level dependent.
There are trade-offs involved when using averaging. Increasing the number of averages maintains wave shape but
decreases responsiveness or how quickly the trace is updated. Likewise, a lower
Filter
setting will provide faster trace
updating but affects the wave shape. This results in a rounded pulse shape because as the filter is narrowed the high
frequency component of the signal is decreased.
The following grahics illustrate measuring a low level signal with
Filter
set first to 10 MHz and then the same signal
with
Filter
set to 200 kHz; in both cases averaging is set to 10. Notice the pulse becomes more discernable from the
noise when the
Filter
setting is reduced in this instance.
