Options

This dialog box displays the gnat options.

Parallel Port I/O Address

Select the parallel I/O port address that corresponds to the port connected to the VNA.

Reserve Printer

Check this box if you want gnat to attempt to reserve a printer device. This means that gnat will attempt to open the printer device specified in the Name control. If the name cannot be opened, that is taken as a sign that the parallel port is in use.

Name

The printer device name of the parallel port. While it is usually the case that the port address and printer name are bound together, this is not always true, so the port address and printer name are specified separately.

Accept and Display KHz as opposed to MHz

This check box controls the behavior of how frequency values are entered and displayed. You should pick the KHz or MHz representation based upon whichever format is more convenient and natural. This control changes the behavior of all frequency controls in gnat.

Master Oscillator Frequency

The VNA master oscillator frequency. Usually, 148.344 MHz. This data value is only used to convert frequency into DDS tuning word values.

Set LO DDS to follow RF DDS Frequency

Normally, the RF and LO DDS frequency values are independent. If this control is checked, the LO DDS will take its frequency value from the RF DDS setting (on the main dialog).

Automatic DDS Setting upon Edit

DDS frequencies are set on the main dialog. Normally, you edit the frequency, phase, and power down state to a set of desired values, then click the Set DDS button to actually change the chips. Although this mode allows all of the changes to be made at once, the problem is that usually the frequency is changed, but the Set DDS button is simply forgotten, and the DDS chips do not change. When this control is checked, each change to the RF and LO DDS controls on the main dialog will be immediately made on the chips.

Power down the DDS Chips after 5 seconds of inactivity

This control enables the automatic power down feature in VNAccess. The time interval is preset at 5 seconds.

Detector Setup Time

The amount of time, in microseconds, between changing the DDS data, and starting a data conversion on the ADC. The time is spent in a busy wait loop.

ADC Conversion Rate

Select the conversion rate of the ADC. The range of choices are currently known possibilities, this does not mean that your VNA can operate at a given rate. In fact, the only guaranteed rate is 7 conversions per second. If you have a LTC2440 ADC, then you will have a choice of 10 rates. If you have the OZ modification for the LTC2410 that allows 4 rates. These rates appear at the end of the list.

ADC Sleep Interval

The amount of time, in milliseconds, that gnat will sleep after starting an ADC reading, but before starting to busy wait for the result. The ADC requires approximately 130 mS per conversion. While it is possible to busy wait for the entire interval, that only bogs down the computer, as it is in a tight loop at full run. Conceptually, the sleep interval could be just a little less than conversion interval, and the gnat program would resume right before the conversion completed. Windows, not being a real time operating system, is under no obligation to restart the program when requested. So, if the sleep interval is too high, gnat will not resume execution in a timely manner, and the conversion rate will drop. On the other hand, if you drop the sleep interval towards zero, you will get ADC conversions at the maximum rate, but the computer will spend more time in busy wait loops.

ADC Overlap Average

This control sets the number of samples which will be averaged in the Overlap Test.

Continuous ADC Readings

ADC conversions will be made continuously on the main dialog if this control is checked.

Report ADC as Volts, not Counts

The ADC data can be reported either as a voltage level, or the raw data coming from the chip. This control selects the format that is used in all ADC displays in gnat.

Detector

Select the detector that gnat should sample. The ADC signal assignment is assumed to follow the extended N2PK parallel port assignments.

Control Signal Mapping

Select the control signal mapping which applies to your VNA hardware. There are two choices. The first is any VNA, whether using the LTC2410 or LTC2440 ADC, which follows the extended N2PK parallel port assignments. The second choice follows the OZ LTC2410 ADC hardware, which uses additional circuitry to provide 4 conversion rates while using the LTC2410.

Accepts changes made to the dialog and closes the dialog window.

Cancel

Discards changes made to the dialog and closes the dialog window.

Help

Brings up the HTML Help Viewer, displaying this page.

Last update: Saturday, October 16, 2004 04:19:30 PM
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