This dialog box starts and stops the Overlap Test. Results are displayed on the dialog.
The Overlap Test holds the RF DDS frequency constant, and moves the LO DDS, which is at the same frequency, through the 32 phase combinations. The ADC conversions occur at a rate determined indirectly by the settings on the Options dialog. The ADC data, and ADC samples per second are reported, as well as a measurement of the time needed to execute a single OUT instruction. A data graph plots the voltage returned from the ADC.
For a good time, run the Overlap Test and watch the RF and LO DDS outputs on a two-channel oscilloscope set to the X-Y display mode.
Frequency
Read-only. Contains the test frequency. This frequency cannot be changed on this dialog. When the dialog begins, the frequency is taken from the RF DDS frequency on the main dialog. The units label will change to follow the MHz/KHz selection on the Options dialog.
Result
Read-only. Displays the data returned from the ADC. The format and label will change to following the Volts/Raw format selection on the Options dialog.
Performance
Read-only. This field displays the number of ADC samples expressed in samples per second. The total number of samples taken is divided by the number of second which have elapsed since the Start button was clicked. The display is updated with each result. Every time that the test is restarted, the number of samples is reset to zero.
Status Window
This window displays a number of data items related to the Overlap Test. One of the data items is the amount of time that it takes to execute a computer OUT instruction. This is provided mainly for software development purposes, where the performance cost of communicating with the VNA may need to be evaluated.
Data Graph
A graph of the ADC result. The left side of the graph is a LO DDS phase of 0 degrees. The right side is a LO DDS of 348.75 degrees. In some cases, due to the pipelined nature of the Overlap Test, the very first reading may represent data from the last ADC conversion, started before the dialog was created. If the trace is not continuous, simply wait until the second pass through the phase values, which will display data complete related to the current test.
An open detector will indicate a straight horizontal line. Other detector signals, such as shorting the RF and LO DDS outputs to the respective RF and LO detector inputs will result in a sine wave shape.
Start/Stop Test
This button starts and stops the Overlap Test.
Close
Closes the dialog. The dialog is dismissed.
Help
Brings up the HTML Help Viewer, displaying this page.
Last update:
Saturday, October 16, 2004 01:35:32 PM
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