Start Frequency (Frequency)

The Start Frequency sets the start (lowest) frequency of the frequency band to analyze. For information on other ways to set the Start Frequency, see Changing Frequency Settings.

The following picture shows Start frequency as compared to the other frequency parameters:

$image\freqStart_wmf.jpg$

When the Start frequency is changed, the VSA changes the Span and Center frequencies, but does not change the Stop frequency, except in these two cases:

If a Start frequency that yields an invalid span is specified, the VSA changes the Stop frequency to maintain a valid span.
If a Start frequency greater than the Stop frequency is specified, the VSA changes frequencies to achieve the minimum valid span.

Display Limits (Trace Blanking)

It is possible to select a negative Start frequency. It is also possible to specify a Start frequency that causes the Stop frequency to exceed the VSA's frequency range.

If a Start frequency below the VSA's frequency range is specified, there will not be anything displayed to the left of the minimum Start frequency. For example, if the frequency range of the VSA is 0 to 39 MHz Megahertz: A unit of frequency equal to one million hertz or cycles per second. and a negative Start frequency is specified, there will not be anything displayed to the left of 0 Hz. This is called Trace Blanking.

Likewise, if a Start frequency that results in a Stop frequency above the VSA's frequency range, there will not be anything displayed to the right of the maximum Stop frequency. In the previous example, there will not be anything displayed to the right of 39 MHz.

Start frequency limitations with 2-channel I+jQ(Ch1+j*Ch2) input mode

For information about Center and Span when using dual channel I+jQ(Ch1+j*Ch2) input mode, see I+jQ Span and Frequency.

Using "Show All Points"

Use the Show All Points parameter (Utilities > Display Preferences > Trace tab) to view the blanked trace data. The Show All Points parameter displays frequency data even if it extends beyond the VSA’s standard frequency and valid data range. The data may contain alias products, so use caution when selecting this parameter.