Anritsu VectorStar ME7838 Series, Maintenance Manual

Page: 42 / 178

3-5 ME7838A/E System Verification—Waveguide Millimeter-Wave System Configuration Performance
3-6 PN: 10410-00306 Rev. F VectorStar ME7838 Series MM
• First, all four screws should be tightened until they just stop (minimum torque) with the mating
surfaces parallel as mentioned in the previous bullet point.
• Any one screw is then tightened to “half” torque.
• The 180 degrees opposite screw to the first one is tightened to half torque.
• Next, one of the two remaining screws is tightened to half torque.
• The last screw (it should be 180 degrees opposite to the one just torqued) is then tightened to half
torque.
• Repeat starting with the first screw and tighten all screws to “full” torque.
• Offset Short Shims have some considerations:
• If the Test Port flange is not of the precision type, there will be no precision index pins to force the
Shim into the correct alignment  it could be 90 degrees circularly off, invalidating the calibration.
Verify the waveguide rectangular apertures match.
• The thickness of the Shim and its Flush Short backing necessitate a longer waveguide captivated
screw than for a standard flange. Note that the threaded portion of this screw only threads into the
Test Port flange. There must be a minimum of three threads into the Test Port flange when the
screw is tightened down  less may damage the flange threads.
• The Flush Short surface should be free of debris, nicks or scratches, especially in the waveguide
aperture mating area.
• The calibration routine will require two Offset Shims of different thicknesses. Ensure that the
correct thickness Offset Shim is attached when called out, or else the calibration will be invalid.
• Offset Shims are sometimes used in LRL calibrations. In this case, of course, they are inserted
between both Test Ports. The captivated screw length required for this application will be
different.
• When a Sliding Load is used in the calibration, the load element position is adjusted via a multiple turn
knob. There may be “arbitrary” reference marks as to load position. The calibration routine requires six
different positions of the load. It is not critical as to the absolute spacing of each position but it is
advantageous to use the majority of the load travel distance for all the positions. Prior to using the
Sliding Load, determine approximately the travel required for the six positions. Do not over torque the
adjustment knob at its travel limits.
• When a captivated screw must be removed (backed out) from a flange (such as when a mating part
already has a screw on its end) and it is inserted past its threaded portion loose in the non-threaded
section, similar attention must be taken as to when starting the screw. It is important that the screw be
perpendicular to the flange as the threads start to catch. This is more difficult when backing out as there
is no way to control the required perpendicularity with the hex driver. You may be able to take
advantage of the knurls on the head of the captivated screw and start by pressing the free threaded end
of the screw back with a finger until it stops at the beginning of the threads and start the revere
threading with your fingers. Once the threads are started, the driver can be used. If the threads start
binding, STOP, forward, and carefully start over.
• All steps of the calibration process ideally should be completed in the minimum possible elapsed time to
minimize uncorrectable errors due to system drift. To help accomplish this, waveguide screws should be
applied to all one port calibration devices (terminations, sliding loads and one-piece offset shorts) prior to
starting a calibration. The assumption here is that device mating will utilize all four screws from the
calibration device side.