AD-A099 525 FEDERAL AVIATION ADMINISTRATION TECHNICAL CENTER ATL-ETC FIG 17/2.1INVEST16ATION OF WILCOX MODEL 5850 VERY HI1GH FREQUENCY OMNIDIRE-ETC(U)APR Al W BELL, J DONG

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INVESTIGATION OF WILCOX MODEL 585B VERY HIGHFREQUENCY OMNIDIRECTIONAL RADIO RANGE SYSTEM

JPART 2)

Wayne BellJames Donf

FEDERAL AVIATION ADMINISTRATION TECHNICAL CENTERAtlantic City Airport, N.J. 1605

INTERIM REPORT

APRIL 1981

Document is available to the U.S. public through .the National Technical Information Service.

Springfield, Virginia 22161.

Prepared for Pk

I. S. DEPARTMENT Of TRANSPORTATION5FEDERAL AVIATION ADINISTRATIONSystems Research &1 1evelophent Service

Washieltom, 1. C. M81 6 01 097

NOTICE

This document is disseminated under the sponsorship ofthe Department of Transportation in the interest ofinformation exchange. The United States Governmentassumes no liability for the contents or use thereof.

The United States Government does not endorse productsor manufactu ers. Trade or manufacturer's names appearherein solely because they are considered essential tothe object of this report.

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Technical Report Documentatien Pqe1.Roport No. 2. G Acc..i. M. 3 Recipient'.C.t.,.,,,.

,. -- Author s <Don

Federal Aviation Administration

Atlantic City Airport, New Jersey 08405 041-305-83013. Typo of net and Period Coveed

U.S. Department of Transportation p Nterim

Federal Aviation Administration

Systems Research and Development Service R ndr

Washington, D.C. 2059015. Supplementary Notes

16. Abstract

T.This report establishes a calibration procedure which employs a space modulationchart to adjust percent modulation for the Wilcox 585B very high frequency omni-directional radio range (VOR) System. This procedure is recommended for solid-state VOR designed systems in which the rotatable goniometer has been replaced bya solid-state unit. Ground and airborne modulation tests were made using aspectrum analyzer for determining percent modulation. Results of these measure-ments indicated 1.5 percent modulation be added to the normal 30 percentmodulation adjustment when made with the detector at counterpoise edge to provideequality between near and far afield modulation measurements.

This project was accomplished under Technical Program Document (TPD) 04-309,subprogram 041-305-830. For further information contact Wayne Bell, ACT-100B.1,or Edward M. Sawtelle, Federal Aviation Administration (FAA) Technical CenterProgram Manager, ACT-100B.1, telephone FTS 8-346-3911, commercial (609) 641-8200,extension 3911. Results of this report will be included in a final reportcovering additional system elements on the Wilcox VOR system.

17. Key Words 18. Distrlibutien Stteent

Solid-State VOR Document is available to the U.S. publicModulation Near and Far Afield through the National Technical Information

Service, Springfield, Virginia 22161

19. Security Clesif. (of this neot) 20. Security Clessil. (of this page) 21 . of Pe oee jIt. Pie.

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TABLE OF CONTENTS

Page

INTRODUCTION I

Purpose IBackground 1Description of the Test Facility 1

DISCUSSION 1

Test Procedure and Results 1General 1Procedure Sequence for Space Modulation Chart INear and Far Afield Equality Measurement 4

CONCLUSIONS 6

RECOMMENDATIONS 8

REFERENCES 8

4A Aim

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LIST OF ILLUJSTRATIONS

Figure Page

I Wilcox Model 5851 Shelter 2

2 Wilcox Model 5851 VOR Cabinets 3

3 Space Modulation Chart5

4 Sample Spectrum Recordings 7

iv

INTRODUCtiN DISCUSSION

PURPOSE. TEST PROCEDURE AND RESULTS.

The purpose of this effort was to GENERAL. The tests were accomplisheddevelop an acceptable calibration pro- with the Wilcox test site operating at

cedure to provide equal readings of a frequency of 109.0 megahertz (MHz).30 hertz (Hz) amplitude modulation (AM) Instrumentation employed in the testingbetween aircraft (far afield) and edge include a Fluke model 8600K digitalof counterpoise modulation indications multimeter, a Hewlett-Packard modelwith a Wilcox 585B very high frequency 7402A recorder, and a Hewlett-Packardomnidirectional range (VOR) System. spectrum analyzer comprised of a model

141T display unit, model 8553B RF unit,

BACKGROUND. and a model 8552B intermediate frequen-cy (IF) unit. Reference numbers I and

This interim report was prepared to 2 were used as guidance in formulatingsatisfy request AAF-410-078-003, on the detector calibration procedure. InFederal Aviation Administration (FAA) addition, the methodology presentedForm 9550-I, for the FAA Technical therein assured that ground measure-Center to investigate ground check ments made with the calibrated field

error components. The request included detector to obtain the space modulation

a statement of the need for an chart did not introduce adjustmentacceptable calibration procedure for errors to the airborne measurements.modulation measurements for a Wilcox The field detector diode nonlinearity

model 585B station. A modified required calibration for preparation of

monitor/field detector to be used in 30 Hz AM space modulation chart. The

the investigation is documented in the Wilcox model 585B VOR System has aFAA Technical Center Letter Report No. solid-state goniometer instead of a

NA-80-27-LR, "Investigation of Wilcox mechanically rotatable unit contained585B VOR System (Part I)," by Wayne in earlier VOR models. Consequently,

Bell. the field detector is moved suc-cessively to the several counterpoise

DESCRIPTION OF TEST FACILITY. ground-check bracket locations toobtain intermediate values between the

Figure I shows the circular metal minimum and maximum.The measured valuesshelter for the Wilcox model 585B VOR of field intensity correspond to radial

System with the modified field detector position measurements made by keepingin a bracket position. The equipment the field detector fixed and rotating

cabinets shown in figure 2 contain a the mechanical goniometer. The basiccomplete dual transmitter/dual monitor procedures in the FAA Handbook AF-system. Included in cabinet No. I are: 6780.4A, "Maintenance of VHF Omnirange

the monitor, VOR test generator, local Equipment," were applied.

control panel, radiofrequency (RF)distribution unit, goniometer, trans- PROCEDURE SEQUENCE FOR SPACE MODULATIONmitter, modulator/power supply/keyer, CHART.terminal board panel, and a blower.Since the cabinets are identical, the The transmitter carrier power, adjusted

control unit and test generator can be to 100 watts, is fed to the northwest

installed in either cabinet. (NW) and southeast (SE) antenna slots.

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FIGURE 2. WILCOX MODEL 585B VOR CABINETS

This is sideband (SB) No. I (sine SB). 6. E1 0 0 1 100 x E proportionsTo accomplish this, disconnect the Emax the scalecarrier out cable and terminate it into to 100a dummy load. Connect the SB No. Ioutput cable to the jack where the g. E1 0 0 - scale proportion to 40carrier output cable was connected. 2.5 for convenient use on theConnect the SB No. 2 output cable to a oscilloscopedummy load. Turn the goniometer poweroff. To develop column E of table 1 the

sequence below is followed. Place theIn preparation of a space modulation field detector at the 45 degree azimuthchart, measured values for the differ- bracket and record the digital volt-ent parameters for various field meter reading at J7 on the monitordetector angles are listed in table 1. panel. Continue recording the volt-An additional counterpoise ground check meter readings for each azimuth bracketbracket is installed at an azimuth of location between 45 and 135 degrees.78.75 degrees, providing another field Figure 3 is a space modulation chartdetector calibration position. plotted from the data in table 1.

The following terms and sequence were NEAR AND FAR AFIELD EQUALITYused: MEASUREMENT.

1. P - Field detector angle (used in With the field detector at the 135lieu of goniometer angle) degree bracket position, the modulation

was adjusted to 30 percent (using the2. B - P + 45 - Azimuth of field standard oscilloscope technique

detector location employed at VOR field sites formeasuring the minimum and maximum 30 Hz

3. sin p = Natural trigonometric value AM modulation). The spectrum analyzerwas connected to a dipole antenna at

4. Percent modulation = 100 the 135 degree bracket position (edge1 - sin p of counterpoise). Spectrums were thenI + sin P recorded using the yagi antenna located

500 feet from the counterpoise.Notice that values for parameters in Finally, airborne spectrums werelines 1, 2, 3, and 4 are related by recorded with the spectrum analyzertheir physical geometry. These values aboard the N-47 (Grumman Gulfstream)can be determined and entered in the aircraft flying inbound at an altitudetable prior to any electrical measure- of 1,500 feet mean sea level (msl), atments. 140 knots, at 90 and 135 degree

radials. During these tests no changes5. E - Field Intensity (measured by were made to the VOR System

digital voltmeter) adjustments.EM = Maximum field intensity at

p - 90 degrees Using the spectrum analyzer technique,

reference 2, the modulation ratioE and EM were measured from the is described as the ratio ofdetected waveforms jack (07) on the sideband (ES) and carrier (EC), i.e.,Wilcox model 585B monitor panel ES

EC

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TABLE 1. VALUES FOR SPACE MODULATION CHART

1 2 3 4Modulation

Degrees Degrees Sin percent

0 45.0 0 10022.5 67.5 0.383 44.633.75 78.75 0.556 28.5745.0 90.0 0.707 17.1667.5 112.5 0.924 3.9690.0 135.0 1.00 0

5 6 7E

Volts E100 E1O0/2. 5

0.01 0 06.85 44.63 17.85

9.40 61.24 24.511.59 75.51 30.214.35 93.49 37.415.35 100 40

The values for this ratio were obtained adjustment would be within the toler-from the recorded spectrums. Samples of ance of 25 to 35 percent levels listedthe spectrums are shown in figure 4 with in reference 3.their average percent modulation for thedifferent test conditions.

CONCLUSIONSAverage values were the same for theairborne spectrum data for the 90- and135-degree radial flights inbound from 1. An acceptable procedure was20 to 7 nautical miles range to the VOR developed for calibration of 30 hertzsite. The modulation value measured (Hz) amplitude modulation (AM) modu-from the yagi antenna, located 500 feet lation for the Wilcox 585B very highfrom the counterpoise, was 0.3 percent frequency omnidirectional radio rangegreater than the airborne value and (VOR). A small correction percentage1.6 percent greater than the value provides equality of modulation cali-measured at the edge of the counter- bration between edge of counterpoisepoise. If the 500-foot ground measure- and aircraft (far afield) measurements.ment is considered far afield andaveraged with the airborne measure- 2. A spectrum analyzer technique toments, the difference between near and measure percent modulation providedfar afield is a modulation percent accuracy to observe the small differ-difference of 1.45 percent. Moreover, ences in near and far afieldwithout any compensation for the measurements.difference, the 30 percent optimum

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3. A small calibration percent REFERENCESdifference 1.45 percent exists betweennear and far afield measured modulationvalues. 1. Maintenance of VHF Omnirange

Zqufi nt E AFIre Ne England RegionSuppleent 670.4A, March 16, 1979.

RECOIOZNDATIONS2. Kanen, Garth M., VHF Omni-directional Radio Range (VOR)

Based on the investigation results, it Electromagnetic Spectrum Measurements,is recomended that: Technical Note, Project 213-060-78,

October 18, 1978.1. The calibration procedure includedherein for obtaining a space modulation 3. United States Standard Flightbe used for solid-state very high Inspection Manual, FAA Handbook OAfrequency omnidirectional radio range PB200.1, Section 201.5, Chg 27,(VOR) systems. May 1977.

2. In a Wilcox model 585B Systememploying a 21-foot diameter counter-poise, a modulation for 30 percentadjustment at the edge of the counter-poise be increased by 1.5 percent tomake near and far afield measurementsequivalent.

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