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diff --git a/communications.mdwn b/communications.mdwn
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@@ -17,6 +17,7 @@ Above, ground control to tower [[WiFi]] antennas, circularly polarized patch ant
*Current Antenna Design*
+- [[CPA v4 tuning|cpa_tuning]]
- [[CPA v4 design|CpaDesignv4]]
- [[TrackMaster 3000 - TBC|TrackMaster3000]]
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+
+[[!meta title="CPA v4 Tuning"]]
+
+# CPA v4 Tuning.
+
+Date: September 2, 2011
+Time: 1300-1700 PDT
+Lab: Portland State University Electromagnetics Lab.
+ 1900 Sw 4th Avenue, Portland Oregon.
+Investigators: Glenn LeBrasseur, K Wilson, Nathan Bergey
+
+## Abstract:
+
+The GPS and ATV Circular Patch Antennas were physically modified in an effort
+to tune them towards the desired design frequencies of 1.575 GHz and 2.39 GHz
+respectively. The original frequencies and the effects of incremental and
+final modifications were measured on an Agilent 5071C ENA Series Network Analyzer.
+
+As a result of these modifications the GPS antenna frequency was changed from
+1.521708 GHz to 1.5707520 GHz by changing the vertical dimension of the
+radiator by (-2.2 mm). The ATV antenna frequency was changed from 2.35 GHz to
+2.39 GHz by changing the vertical dimension of the radiator by (-0.8 mm).
+
+## Introduction:
+
+After testing at NW EMC (see [[news/2011-08-12]]) and some experimental work at
+the PSU Electromagnetics Lab (see [[news/2011-08-19.mdwn]) it was decided to
+tune the GPS and ATV antennas by modifying the geometry of the antenna radiator
+sections. No modifications were performed on the feed network.
+
+This report includes the techniques used to modify the CPAs, the measurements
+obtained at each step of the modifications and the theory used to generate
+expected results and decide on the magnitude of each incremental modification.
+
+## Experiment
+
+The differential change in antenna frequency is proportional to the differential
+change in the vertical dimension (X) of the antenna radiator.
+
+[[!img cpa4_tune_diagram.png size="500x231" alt="CPA Tuning Diagram"]]
+
+By measuring the current dimension of the radiator, and the current frequency
+of the antenna an estimate of the necessary adjustment can be made.
+
+ X_d = (f_c/f_g) * X_c
+
+Where:
+ - X_d = delta X, the amount to change X (mm)
+ - f_c = current frequency (Hz)
+ - f_g = goal frequency (Hz)
+ - X_c = current value of X (mm)
+
+Dimensional measurement was performed with digital calipers.
+N.B. Digitial calipers must be calibrated ('zeroed') prior to each measurement.
+
+Each incremental modification to X_d was on the order of (-1 mm). A 'snap knife'
+or thin sharp blade was used against a metal guide held in place around
+the cyclinder of the CPA. The metal band and guide are removed during testing
+of the antenna. The following photo shows the CPA antennas with the metal band.
+In the background is the Network Analyzer with the calibration setup.
+From top to bottom the antennas are GPS, ATV and Wifi.
+
+[[!img CPAwithCal.jpg class="picture" alt="CPA With Metal Guide Band and Network Analyzer Calibration Setup in Background."]]
+
+This photo shows a closeup of the metal band in preparation for a cut.
+
+[[!img MetalBandCloseup.jpg class="picture" alt="Metal Band Closeup."]]
+
+Early cuts were made with a heavy utility knife and blade. It was found that using
+a sharp 'snap knife' device, it was easier to control the alignment against the
+metal guide.
+
+[[!img NeverUseThis.jpg class="picture" alt="Never Use This."]]
+
+Cut control was best achieved by alternating cutting and turning the CPA array,
+while observing the blade from a position that minimized parallax.
+At least two full rotations were made during cutting. The first orbit cut
+through the F4 PCB top layer and the second orbit through the thin
+copper layer. The two cuts will have a different 'feel' to the operator.
+The F4 layer is fibrous and slower to cut while the copper is smooth
+and cuts more quickly.
+
+[[!img MakingACut.jpg class="picture" alt="MakingACut."]]
+
+[[!img MakingACut2.jpg class="picture" alt="MakingACut2."]]
+
+[[!img RemovingMaterial.jpg class="picture" alt="Removing Material."]]
+
+[[!img Skive1.jpg class="picture" alt="Skive."]]
+
+[[!img Skive2.jpg class="picture" alt="Another Skive."]]
+
+## GPS CPA Tuning Results
+
+### Initial GPS NA Measurements
+
+img1
+img2
+
+<table>
+ <tr>
+ <th>GPS CPA Tuning</th>
+ </tr>
+ <tr>
+ <th>X_c (mm)</th>
+ <th>X_d (mm)</th>
+ <th>f_c (GHz)</th>
+ <th>f_g (GHz)</th>
+ <th>Measured Frequency</th>
+ </tr>
+ <tr>
+ <td>62mm, 1mm, 1.521708GHz, 1.575420GHz, 1.54422GHz </td>
+ <td>61mm, 1mm, 1.54422GHz, 1.575420GHz, 1.570520GHz </td>
+ </tr>
+</table>
+
+### First Cut NA Measurements
+
+img3
+img4
+
+### Second Cut NA Measurements
+
+img5
+img6
+
+The final frequency achieved was 99.7% of the goal frequency.
+
+It was decided to cease making any adjustments to the GPS antenna at
+this point.
+
+## ATV CPA Tuning Results
+
+Calculating the X_d for this antenna resulted in a requirement
+for X_d = (-0.5mm). This is expected to be the minimum manageable
+amount of material to skive off the antenna. The actual measured
+amount removed was closer to X_d = (-0.8mm). This is also close
+to the minimum distance measurement capability of the digital
+calipers. The actual amount removed is expected to be between
+0.5mm and 0.8mm. It is listed in the table as 0.5mm, which was
+the target amount.
+
+<table>
+ <tr>
+ <th>ATV CPA Tuning</th>
+ </tr>
+ <tr>
+ <th>X_c (mm)</th>
+ <th>X_d (mm)</th>
+ <th>f_c (GHz)</th>
+ <th>f_g (GHz)</th>
+ <th>Measured Frequency</th>
+ </tr>
+ <tr>
+ <td>39.6mm, 0.5mm, 2.35GHz, 2.39GHz, 2.39GHz </td>
+ </tr>
+</table>
+
+###Initial ATV NA Measurements
+
+(Not available? See elsewhere?)
+
+### Post Cut ATV NA Measurements
+
+img7
+img8
+
+Discussion of -5db performance change?
+
+
+#### Messy Lab Books are OK in PSAS!
+
+[[!img messynotes.jpg class="picture" alt="Messy Books ok by us!"]]
+
+
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