Selecting the Optimum Range Value

If the input range is set too low (more sensitive than necessary), the VSA's ADC Analog-to-Digital Converter circuitry introduces distortion into the measurement. But if the input range is set too high (less sensitive than necessary), there may be a loss of dynamic range due to additional noise--in some cases, the increase in the noise floor may even obscure low-level frequency components.

If OVx (where x is a channel number) appears in the Trace Indicator, the ADC circuitry is being overdriven. In this case, change to a less sensitive range or reduce the input signal level.

The input circuitry is sensitive to all signals within the VSA's frequency range--including those that are outside the current span.

Signals that are outside the current span MAY overload the ADC circuitry--causing measurement error.

Always set the range as the first step in setting up a measurement. Setting the range properly affects the input signal processing and must fulfill two conditions. First, avoid overloading the input because overdriving the ADC module causes the signal to be digitized inaccurately. The second condition is to select a range that provides the best dynamic range over the entire frequency range of the instrument.

Remember that Scaling doesn't affect either of these conditions, because Scaling just acts on the display.

To examine a particular portion of the signal (such as a sideband), adjust the frequency span or center frequency but do not change the range setting.