Abstract: A method for simulating an analog display in a digital display spectrum analyzer (or other digital display test instrument) comprises the steps of defining a plurality, N, of traces of the signal to be displayed, assigning coordinate values to points along each trace, and plotting and simultaneously displaying each of the N traces by illuminating corresponding pixel locations on the CRT as indicated by the assigned coordinate values. The method permits effective simulation of trace persistence as commonly found in analog display test instruments. According to one embodiment of the invention, a color graphics controller/color CRT may be provided, in which case gray scales may be generated and displayed to simulate variations in intensity levels as commonly found in traces plotted on analog display test instruments. An apparatus for practicing the method is also disclosed.

Abstract: Upon the adjustment of a control setting of a test instrument, the current data (taken before the change is effected) is manipulated by recalculating the trace data in light of any adjustment that is entered by a user. This represents an estimate of the effect of the adjustment in the control setting, and this estimate is redrawn on a display device. This modified image is preferably displayed before the real new image is ready to be displayed. This provides immediate feedback to the user so that adjustments can be effected without slowing the measurement process. Various embodiments provide panning or repositioning the trace left and right while changing the x-axis center frequency; stretching or compressing the trace (spanning) while changing the frequency span; or using a combination for adjustments to only the start or stop frequency. In one embodiment, the estimate can be displayed only after the user has committed to having a new measurement performed.