Operational Descriptions for the MSA
in Vector Network Analyzer Modes

Page Started Aug. 1, 2009

    B.  Vector Network Analyzer Operation
        1.  VNA, Transmission Mode
         
Controls for the VNA, Transmission Mode
         
Special Testing in the VNA, Transmission Mode
            Phase Detector Module Control
            Phase Detector Module Sync Test
            VNA Phase Error Test
          Using the Features of the VNA, in the Transmission Mode
        2.  VNA, Reflection Mode (under construction)

B.  Vector Network Analyzer Operation
    A Spectrum Analyzer will measure the absolute Magnitude of a signal.  A Vector Network Analyzer will measure not only a signal's Magnitude, but also its Phase.  The Phase is somewhat meaningless unless the signal can be referenced to another signal at the same frequency.  This is why all VNA's have a Tracking Generator used as a Reference Source.  A commercial VNA uses its Tracking Generator output as the Reference Source.  The MSA/VNA uses the base frequency of 10.7 MHz as its Reference Source.
    The purpose of any VNA is to quantify the electrical characteristics of an unknown Device.  A
device can be a passive or active part, a piece of coaxial cable, a Reflection Bridge, or even an antenna, to name a few.  Any Device will change the Magnitude and Phase characteristics of a signal passing through it.  By measuring a Device's output signal and comparing it to it's input signal, the Device's parameters can be calculated and quantified.
    In many cases a  Device can be a combination of multiple devices, such as a Bridge (with connector adapters), and a crystal filter (inserted in a test bed).  This requires multiple measurments, to factor out characteristics of all known supporting "Devices" to determine the characteristics of the final unknown Device, the Device Under Test (DUT).  In this case, just the crystal filter.
    The VNA can measure in several different modes.  But, in all modes the VNA is simply measuring the Magnitude and Phase of a Device's output signal and comparing it to the Magnitude and Phase of the Device's input signal.  The specific Mode determines how the four quantities of Magnitude and Phase are processed and displayed.  At this time, the MSA/VNA has these Modes of operation:
1. VNA, Transmission Mode:
    S21 Magnitude, S21 Phase Angle, and
S21 Group Delay
    The Transmission Mode is simply specifying that the VNA is making measurements in the Forward Direction.  That is, measuring the output of the Device and comparing the results to the input of the Device.
2. VNA, Reflection Mode: (under construction)
    The Reflection Mode is still comparing a Device's output to input, but the Device will usually consist a Reflection Bridge attached to an unknown Device Under Test.

1.  VNA, Transmission Mode
    When entering the VNA Transmission Mode from the Spectrum Analyzer Mode, sweeping will automatically begin with default values left over from the SA Mode.  The following is a screen print of the Graph Window while sweeping from 0 to 1000 MHz.  The Tracking Generator output is connected to the input of the MSA throught a 4 inch test coax and two 10 dB attenuators.  Two signal parameters are displayed in the Graph Window.  The Magnitude trace indicates the power level of the input signal to the MSA, with its reference scale on the right side.  The Phase trace indicates the phase of the input signal.  The Phase reference scale (in degrees) is on the left side.
operation/operate/vnatran1.gif
    Notice that there are several Phase "sawtooths" displayed, one for each rotation of 360 degrees.  This is because the Signal frequency is changing, but the Reference frequency is not.  The number of rotations will differ for each separate VNA.  It is due to the internal and external lengths of cable which add time delay to the measured signal.  A Reference Calibration would normalize the Phase of the Signal to the Phase of the Reference and the trace would become flat.  This is a good self test, indicating that everything in the MSA is functioning normally.

Controls for the VNA, Transmission Mode
    All of the Controls that were described in the Spectrum Analyzer Mode are included in the VNA Transmission Mode.  They need not be repeated here.  I will describe only the differences.
Indicators
    "Marker" Table displays the marker's Magnitude measurement as S21 dB and the Phase measurement as S21 Deg.

Boxes and Buttons
    All of the Boxes and Buttons that were described in the Spectrum Analyzer Mode are included in the VNA Graph Window.  They need not be repeated here.  Differences are:
    The "Marker" Table displays the marker's Magnitude measurement as S21 dB and the Phase measurement as S21 Deg.

Windows within the Graph Window, normally hidden.
The Sweep Parameters Window
    Most of the Controls that were described in the Spectrum Analyzer Mode are repeated in this window.  These are the exceptions and additions for VNA Modes:
    The "Spur Test" button is deleted.  Spur testing is meaningless during VNA operation.
    The selection of Signal Generator or Tracking Generator is deleted.  The Tracking Generator is automatically selected during VNA operation.
    Note: The "Select Final Filter Path:"  drop-down box must have the correct Path selected for VNA operation.  All VNA calibrations are performed in a single Path.  Usually, this is Path 1.
    "PDM Inversion (deg) box.  This box displays the current calibration for the PDM.  It can be changed in this box for special testing.
    "Plane Extension" box.  This adds or subtracts (-) time into the calculations.  It is the same as physically adding cable length within the Reference Source circuit.  This is a very good way to factor out time delay effects of transitional components surrounding the DUT, such as barrel connectors, test jig, etc.  Just for reference, the Verification unit requires a plane extension of "3.2" ns to factor out its internal delays.

The Magnitude Axis Window
    All of the Controls that were described in the Spectrum Analyzer Mode are repeated in this window, with these exceptions:
    The "Trace Style" pull down box does not have options for a Histogram trace.
    The "Graph Data" pull-down box has 2 selections:
     * S21 Magnitude is the default and a common reference for VNA's.
     * Magnitude (Ratio)

The Phase Axis Window
    While Halted, position the mouse cursor over any of the Phase Scale values and double left click..
The "Axis Y1" Window will open.  It contains the buttons and boxes used to control the parameters of the phase trace.
    "Trace Color" box.  Click within the box to open a Color Window.  You may choose a variety of colors for the trace.
    "Trace Width" pull-down box.  You may select 3 different trace widths.  The numbers correspond to the number of pixels used for drawing the trace. "1" is default and works best.
    "Trace Style" pull-down box.   This box has 3 selections for the desired trace.
    *  "Off"  The trace will not be displayed the Graph Window.  However, the data will be collected and the Graph Markers will update.
    *  "Erase" The data point is connected to the previous data point by a line.  Each trace will remain on the graph until the next sweep, where it will be erased and re-written at each step.  This is the most common display for network analyzers.
    *  "Stick" Same as Erase, except the traces will not be erased.  They will be overwritten by subsequent sweeps.  This is useful for accumulated peak readings.
    "Number of Divisions" pull-down box.  You may select the number of horizontal graph reference lines, from 4 to 12.  A selection here will also affect the Magnitude scale, the Y2 axis.
    "Graph Data" pull-down box.  This will define the Scale and Trace to display the data in one of two measurement options:
    *  "S21 Phase Angle.  This is the common measurement for a Spectrum Analyzer.  The Phase is measured and scaled in degrees.
    *  "S21 Group Delay.  The Phase is measured in degrees but scaled in the time domain.
    "Auto Scale" check box.  A check will allow the program to create a scale that is appropriate for the measurement.  Apply a check mark here when changing an option in the "Graph Data" pull-down box.  This will assure a trace on the graph.  Uncheck this when manually entering values into the "Top Ref" or "Bot Ref" box.
    "Top Ref" box.  and  "Bot Ref" box.  Numbers entered into these boxes will assign the Reference values for the vertical scale on the Graph.
    When graphing Phase Angle, the "Top Ref" scale value can be anywhere between 360 and -359.9 (in degrees), with a resolution of .1 degree.  The "Bot Ref" can be anywhere between 359.9 and -360, but its value must be more negative than the "Top Ref".  The difference between the "Top Ref" and "Bot Ref" must not be greater than 360.  The default values are 180 and -180.
    When graphing Group Delay, the scale is in Seconds.  You may enter scale values into the "Top Ref" or "Bot Ref" box with a suffix of u (microseconds), n (nanoseconds), or p (picoseconds).  The "Bot Ref" can not be less than 0.
    "OK" button.  Clicking will close the window and cause the program to use any changes made within the window.
    "Cancel" button.  Clicking will close the window and any changes made within the window will be disregarded by the program.

Graph Menu Items
    The same Menu Items for the Spectrum Analyzer are used for VNA, Transimission Mode but these are the differences:
[Options]
    [Transmission Setup] 
This will open the window, "Transmission Measurement Setup".  This configures the software to match the physical configuration of the Device Under Test.  More to be written on this procedure.

[Setup]
    [PDM Calibration] 
This will open the "PDM Calibration Manager" window.  This window will allow the operator to calibrate the Phase Detector Module.  It will be referred to during the Calibration Procedure for the MSA.

[Data]
    The following sub-menu items are in addition to the items that were described in the Spectrum Analyzer Mode:
    [Magnitude Calibration Table] - This will open a Data Window and display two columns of values, with one row of values for each step, for one full sweep.  These values represent the Frequency and absolute power level of the input signal to the MSA, when the VNA performed a Line Calibration.  These values are normally subtracted from the Magnitude Data to create a relative Power gain/loss measurement.  If not in the VNA Mode, these values are meaningless.  This is a place holder and I have a lot more work to do here.
    [Phase Data, Processed] - This will open a Data Window and display two columns of values, with one row of values for each step, for one full sweep.  These values represent the Frequency and Processed Phase of the input signal in the VNA Mode.  It is the difference between the absolute phase of the input signal and the absolute Phase data taken during a Line Calibration.  This is a place holder and I have a lot more work to do here.
    [Phase AtoD Bits] -
This will open a Data Window and display two columns of values, with one row of values for each step, for one full sweep.  These values represent the Frequency and Bit count of the Phase Analog to Digital Converter.  This is a place holder and I have a lot more work to do here.
    [Phase Calibration Table] - This will open a Data Window and display two columns of values, with one row of values for each step, for one full sweep.  These values represent the Frequency and Absolute Phase of the input signal after the VNA has performed a Line Calibration.  It is used to create the Processed Phase.  This is a place holder and I have a lot more work to do here.
    [S21 Parameters] - This will open a Data Window and display a table of S21 Parameters.  It is in a Touchstone format.

[Operating Cal] This menu item is not shown in the Spectrum Analyzer Mode.
    [Perform Cal] - This will open the window, "Perform Calibrations".  This will allow the operator to perform a Reference Line Calibration, which preceeds a standard VNA measurement.  This calibration will "normalize" the sweep to 0 dB for Magnitude and 0 degrees for Phase.  After this calibration, all sweeps will be Referenced to this "normalized" calibration.  When either of the following calibrations are performed, insure that the Plane Extension is "0", found in the "Sweep Parameters"  window.
    The Band Sweep Calibration will calibrate the VNA for a specific frequency range.  The calibration values are stored in local memory and will be deleted when the MSA session is closed.  The accuracy of the VNA is valid only when the subsequent sweeps are identical to the sweep frequency that is calibrated.
    The Baseline Calibration is normally the sweep frequency range of the MSA/VNA, which is .1 MHz to 1000 MHz. (VNA's do not like 0 Hz).  This calibration is stored in a file, that is placed into the same folder as the MSA software.  It is not deleted at the end of the MSA session.  It will be valid for all future sessions.  However, this is a rather course calibration, and VNA measurements will not be accurate.  But, it is a valuable for "ballpark" measurements.  A one month variation in the Verification Unit showed that the Baseline Cal had shifted less than 4 degrees and had a ripple of less than .5 degrees.
    [Reference To] - This will open the window, "VNA References".  This will allow the VNA to reference its measurements to the appropriate calibration table.  On initial running of the VNA, the Cal tables are filled with zeros.  It is the same thing as selecting "No Reference".  If a Baseline Calibration has been performed, the file will be accessed and the calibration will be valid.  "No Reference" is the default.

Special Testing in the VNA, Transmission Mode
    This section will describe special testing of the MSA while in the VNA Mode.
"Special Tests" window.
    Click the menu item, Setup, and select Special Tests.  The "Special Tests Window" will open and display several items.  Only those items that are relevant to the VNA Mode will be described.


Special Test:  Phase Detector Module Control
    "Change PDM" button.  This will control the phase inversion of the Phase Detector Module (PDM).  During normal VNA Mode sweeping, the software is constantly reading the phase data.  If the phase data is ever out of linear range of the PDM, the software will automatically invert the Reference Signal inside the PDM.  This 180 degree phase inversion guarantees phase data accuracy.
    In some special testing, it is helpful to disable this automatic feature and assure that the PDM is fixed in one of it's inversion states, either "Normal" or "Inverted".
Follow these steps for proper operation.  The MSA must be in the "Halted" condition:
    Open the Special Tests Window, and click the "Change PDM" button.  The PDM will be commanded to "Normal", immediately.  The button will change it's name to "PDM in Normal".  Click "Restart" to resume sweeping.  The PDM will remain fixed in its "Normal" state, and will not change during sweeping.  Halt the sweep.
    When the
"PDM in Normal" button is clicked, the PDM will be commanded to "Inverted", immediately.  The button will change it's name to "PDM in Inverted".  Click "Restart" to resume sweeping.  The PDM will remain fixed in its "Inverted" state, and will not change during sweeping.  Halt the sweep.
    When the "PDM in Inverted" button is clicked, the button will change it's name to "PDM is Auto".  No command is immediately sent to the PDM.  Click "Restart" to resume sweeping.  The PDM will return to automatic operation during sweeping.
    As long as the Special Tests Window is open, the PDM will remain in one of the commanded modes.  Operator actions within the MSA Working Window will not change the state of the PDM.  When the
Special Tests Window is exited, the PDM will revert to automatic operation.

Special Test:  Phase Detector Module Sync Test
    "Sync Test PDM" button.  This is a special test I wrote for verification of the first SLIM VNA.  It has no practical use but, it is quite handy to determine the functionality and quality of the PDM, and it looks cool.  For a more critical test, use the Special Test:  VNA Phase Error Test.
    Configure the MSA/VNA:
Remove any signal that may be on the input to the MSA.
Select the Phase Video Selector Switch to "Medium" or "Wide".
In the Sweep Parameters Window, uncheck the "Refresh Screen Each Scan" [OK].
    Open the Special Tests Window and click the "Sync Test PDM" button.   The following will occur:
The Center Frequency of the sweep will be commanded to 0 (MHz).
The Sweep Width will be commanded to
0 (MHz).
The Wait box will be commanded to "3".  The "3" is an arbitrary number that works well for my computer.  It can be changed to a higher value to plot more sawtooths.
The right magnitude scale is changed to +5 (dB) to -5 (dB).
The left phase scale is changed to 360 degrees (top) and 0 degrees (bottom).
The markers are removed from the graph.
The PDM is set to "Normal" and not allowed to change inversion states.
Sweeping will automatically start.
The Tracking Generator output will be very close to 0 Hz but it is not used.
    The VNA is now collecting and displaying the phase differential of the two signals entering the PDM.  The two signals are the Limited I.F. signal from the Log Detector and the Reference Signal created by the Tracking Generator.  In normal VNA operation, the Tracking Generator Signal is the Reference signal.  It passes through the Device Under Test and enters the MSA input.  The two signals at the PDM are extremely close to the same frequency, and of course, out of phase.
    In this special test, the Reference signal into the PDM is still created by the Tracking Generator (PLO 3), but the Limited I.F. signal is created by the first Local Oscillator (PLO 1).  Both PLO's are commanded to 1013.3 MHz, however, the two signals are not quite the same frequency.  They are usually within 1 Hz of each other.  This creates a "false" phase display, which is constantly rotating at the rate of the difference in the two frequencies.  When the sweep finishes it's final step, it will not immediately return to the first step and continue sweeping.  It will wait until the phase differential is approximately 290 degrees and then restart the sweep at step 0.  This is the "sync" part of this special test.  This allows "somewhat" repeatable traces in the Graph Window.  After a few initial sweeps, if the sweep does not sync, halt the sweep and play with the value in the "Wait" box (Sweep Parameters Window).  Click [Continue] or [Restart].  Do not move the Mouse during sweeping.  This causes the computer to "housekeep" and the trace will become quite erratic.   Normal computer "housekeeping" will "mess up" this test, so keep this in mind.  Leave the Special Tests Window open during this test, even if it is hidden behind one of the other Windows.  If it is closed, the test will work improperly.
    What you see on the Graph:
operation/operate/synctest.gif

    The Phase trace (sawtooths)
is the phase differential of the two inputs to the PDM, using the left scale.  It is indicating the rotations of the PDM input signals. The number of rotations per sweep are dependent on many things but can be controlled by changing the value "Wait" box.
    The top of each sawthooth is flat, and the bottom of the sawtooth does not reach 0 degrees.  With a "perfect" phase detector, the sawtooth would reach the 360 degree reference line and immediately transition to exactly 0 degrees.  This Phase Detector is not perfect.  It has an area of "uncertainty", which is called the "dead zone".  This "dead zone" is indicated by the phase distance between the first "touch" of the sawtooth at 360 degrees, to the transition near the base of the graph.  In this case, it is about 15 degrees.
    Outside, but close to this "dead zone", we expect the PDM to be unlinear.  Nonlinearity would be indicated when the sawtooth is not a straight line.  Due to the large scale factor, this unlinearity of the sawtooth is difficult to see.  Therefore, we can decrease the scale factor and use a different trace to show unlinearity.  We can use the "Magnitude" trace for this.
    The Magnitude trace is not magnitude at all.  It is the amount of phase change for each step in the sweep, using the right dB scale as degrees.  This value will depend upon the speed of the sweep and the difference in the two frequencies entering the PDM.  Prove this by halting the sweep, change the value in the "Wait" box, and [Continue].  The trace is quite noisy, due to the phase noise of the PLO's and the Video bandwidth selection.  For best PDM linearity, we are looking for a flat trace (no trend), discounting the peak to peak noise.  A general slope or shift in the trace indicates deviation from linearity.   In the graph, the PDM is showing a very flat trend (linearity) except within the area of the "Dead zone".  The VNA software does not allow phase data to be used within the limits of -72 degrees (+288 deg) to +72 degrees.  Therefore, this PDM has a great deal of margin.
    To return to normal VNA operation, Halt the sweep and close the Special Tests Window.  Open the Sweep Parameters Window and select your appropriate parameters.  The Magnitude and Phase scale windows must be changed also.  It may be quicker to just close this session of MSA and re-start it.

Special Test:  VNA Phase Error Test
"Preset VNA Linearity" button.  This test is a very accurate method of measuring VNA Phase Error.  However, all VNA Phase Error is factored out during normal VNA measurements when a Reference Line Calibration has been performed.
    Manually configure the MSA/VNA:
Install a 50 ohm test cable from the Tracking Generator Output to the MSA Input.  A minimal length cable (3 inches) will test the Phase Error of the complete VNA.  A very long cable (10 ft. to 100 ft.) will minimize the error contributions of the components external to the PDM.  Mainly, it will reduce the error created by the Mixer 4 (AM to PM conversion) and the PDM will be the major contributor to error.  We will use this configuration to measuring the Phase Error of only the PDM.  I used a 118 feet of RG-188.
Select the Phase Video Selector Switch to "Medium" or "Wide".
    Open the Special Tests and click the button called "Preset VNA Linearity".   When this button is clicked, the following will occur:
The button will change it's name to
[Test Transmission Linearity].
The Center Frequency of the sweep will be commanded to 500 (MHz).
The Sweep Width will be commanded to 100
0 (MHz).
The Wait box will be commanded to "22".
The right Magnitude scale is changed to +5 to -5, we will use this as the error scale.
The left Phase scale is set to +180 degrees (top) and -180 degrees (bottom).
The PDM (Phase Detector Module) is set to "Normal" and not allowed to change inversion states.
Sweeping will automatically start.
    The Magnitude trace will display the MSA input power, but it is likely to be outside of the +5 to -5 graph limits.  Disregard the trace, Magnitude is not used in this test, anyway.

    The VNA will sweep from 0 to 1000 MHz, and display multiple sawtooths, the number depending on the length of the cable between the TG output and the MSA input.  Each sawtooth represents 360 degrees of phase change.
operation/operate/vnaerror1.gif
    Halt the sweep.  We now want to choose one of the sawtooths to analyze.  In this example, there are approximately 100 sawtooths displayed.  Position an "L" marker and an "R" marker spaced by a few sawtooths.  See markers in example above.
Click the "ExpandL-R" button.
The sweep will resume, with only a few sawtooths.  See example below.
Halt the sweep.
You will now notice that each sawtooth has a "glitch" in its slope, at approximately 0 degrees.  This is
the 0/360 degree "dead zone".  This is caused by having the PDM fixed at "Normal".
Position an "L" marker on one of these "glitches" and an "R" marker on a "glitch" to the right, separated by two full sawtooths.  See the example below.
operation/operate/vnaerror2.gif
Click the "ExpandL-R" button.
The sweep will resume, with only two sawtooths.  See example, below.
Halt the sweep.

    We now want to choose only one of the sawtooths to analyze.  Note that, the center horizontal scale line represents 0 degrees (left scale).  Each other horizontal scale line represents 36 degrees separation from 0 degrees.
Select Marker "L" and position the Mouse Curser about 36 degrees left of the wanted sawtooth's 180 degree transition.  This is the crossover at -144 degrees.  Right Click the Mouse.
Select Marker "R" and position the Mouse Curser about 36 degrees to the right of the second sawtooth's 180 degree transition.  This is the crossover at +144 degrees.  Right Click the Mouse.
operation/operate/vnaerror3.gif
Click the "Expand L-R" button.
The sweep will resume, with only one sawtooth.
Halt the sweep.

  You should end up with a trace in the Graph Window that looks similar to the following:
operation/operate/vnaerror4.gif
    The phase trace indicates the phase differential at the Phase Detector Module.  The phase will change as the frequency changes, due to the total line lengths within the VNA plus the length of the external test cable.
  Somewhat more than a single sawtooth is displayed, more than 360 degrees.
    Imagine a straight-edge ruler on the monitor screem, directly over the +180 deg to -180 deg slope.  In a perfect VNA and perfect PDM, the slope would be as straight and flat as your straight-edge ruler.  Any deviation from a straight line would indicate the total VNA Phase Error.  There is an obvious deviation near the 0 degree crossover.  This is the PDM's "dead zone". 
The straight edge test is impossible to do with such a large scale, so we can add another trace with a very small scale.  This is the next portion.
    Before entering (and during) the next portion of the test, verify that the Phase trace in the Graph represents more than one full sawtooth, and less than two.  That is, the trace is at least 360 degrees and less than 720 degrees.  It is also important that the first and last steps in the sweep are on the linear portion of the sawtooth.  If not, change the Center Frequency and/or the Sweep Width until the criteria are met.

    Position the Mouse Pointer anywhere on the Phase sawtooth except near the "dead zone".  This point will become the Reference for the next portion of the test.
Left Click the Mouse.  A double click will insert the "L" Marker.
Click the "
Test Transmission Linearity" button in the Special Tests Window.
    The Graph will clear and repeat the previous sweep, but now adding a trace to indicate the Phase Error of the VNA (right scale).  The Phase Error is any deviation from the straight line of a "theoretically perfect" sawtooth slope.  The software calculates this error by measuring the actual phase at each step and comparing it to a theoretical phase measurement
.  When the sweep is Halted, a phase/frequency factor will be displayed in the Message Box, in degrees per MHz.  This value (-72.01) is dependent of the length of test cable.  The Phase Error will be displayed in the Marker box as S21 dB.operation/operate/vnaerror5.gif
    Read the right (dB) scale as "phase error, in degrees".  The Phase error will be 0 degrees at the Reference Point, Marker "L".  You will notice an upward "trend" in the Phase Error trace.  It begins at Marker 3 and ends at Marker 4.  This is the Error contribution of the VNA components, outside the PDM.  If it were a PDM contribution, the Marker 4 would revert to the same level as Marker 3.
    The Error trace looks have peak to peak noise of +/- 0.2 degrees.  This is not noise, it is the frequency to phase conversion that is created within the Final Crystal Filter of the MSA.  During the sweep, the final I.F. deviates a few Hertz, and very narrow bandwidth Crystal Filters will exaggerate this FM to PM conversion.  This is especially noticeable on the Phase error trace below the "L" marker.
    The "dead zone" of the PDM is clearly indicated where the Phase trace is transitioning near zero degrees.  The phase error is so large, it leaves the boundries of the +5 degree, -5 degree right scale.
    This data was taken with the first SLIM MSA/VNA.  It's PDM had been modified to use a "pulse trigger" scheme in place of a "one shot". 
The uncertainty of the "pulse trigger" is indicated by the error trace to the right of the "dead zone".  The PDM's "non-linearity area", including its "dead zone", is indicated between Markers 1 and 2.  This is from 18.48 deg to -16.72 deg, a total of 35.2 degrees.  This PDM is indicating excellent Phase Error.  It looks to be about .1 degrees.
    The Reference Point can be changed and a new sweep initiated.  Halt the Sweep, left click a different reference point, and click the "Test Transmission Linearity" Button.  You can also halt and change the scales, Center Frequency, or Sweep Width.  But, you must click [Restart] Button after any change.  The previously determined phase/frequency factor and Reference point will be used for all new sweeps if the [One Step], [Continue], or [Restart] buttons are clicked.  Clicking the "Test Transmission Linearity" Button will update the Reference Point and recalculate the phase/frequency factor.
    To return to normal VNA Mode operation, exit the Special Tests Window by clicking the "X" button.  The values that were placed in the Graph Window will "stick" there until the operator changes them.
    Even though this test may indicate Phase Errors, those Errors are factored out when a Reference Line Calibration is performed before a normal VNA measurement.

Using the Features of the VNA, in the Transmission Mode
    This section is under construction.
Component Testing
    Crystals, Filters, Attenuators
    Resistors, Capacitors, Inductors

2.  VNA, Reflection Mode
Open the Magnitude Axis Window and
Open the Sweep Parameters Window and