Parabolic Antenna Alignment Procedure

7/21/2019 Parabolic Antenna Alignment Procedure

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Rep. 1740 Data 16/05/2005 Ed. 1 Em./Var. Firma Escudero

Esec. Elifani Contr Escudero

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Parabolic Antennas Al ignment procedure - 1/16- Mod. 151-204/66Ed. 02

Basic MW Antennas Alignment

Guide Line for split MW System





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Index

1 INTRODUCTION.............................................................................................................. 3 2 ALIGNMENT FUNDAMENTALS...................................................................................... 3 2.1. Azimuth Location.......................................................................................................... 3 2.2. Levelling Antenna......................................................................................................... 5 2.3. Pole fixing..................................................................................................................... 5 2.4. Antenna Polarization (single polarization antenna)...................................................... 6 2.5. Antenna Polarization (double polarization antenna) .................................................... 7 2.6. Radiation Pattern and Signal Strength......................................................................... 8 2.7. Tools and Tests instruments........................................................................................ 9 2.7.1. Mechanical Tools ................................................................................................... 10 2.7.2. Test Instruments..................................................................................................... 10 3 PATH ALIGNMENT PROCEDURE................................................................................ 12

3.1. Basic procedure ......................................................................................................... 12 3.1.1. Adjusting the antenna ............................................................................................ 13 3.1.2. Vertical adjustment of antenna............................................................................... 14 3.1.3. Fine adjustment of antenna.................................................................................... 14 3.2. Step by step Basic ..................................................................................................... 15 3.2.1. Standard Link (one antenna per site)..................................................................... 15 3.2.2. Link in Antenna Diversity configuration and / or Hot Stand-By system (Twoantennas per site) .................................................................................................................. 15 3.2.3. Link in Antenna Diversity configuration and / or Freq. diversity system (Twoantennas per site) .................................................................................................................. 16





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1 INTRODUCTION

For a reliable microwave link communication between two terrestrial radio sites, fundamental is a correct antennasalignment.

Parabolic microwave antennas can be aligned using either a customer supplied radio, independent path alignmenttransceiver set or other properly tools and test instrument related to the equipments specifications.Microwave antennas must be accurately positioned on true azimuth and be absolutely level before beginning pathalignment. Most alignment difficulties are the result of incorrect azimuth position or inadequate levelling.

Target of antennas alignment is to adjust the properly direction of both antennas (site A and B), in order to obtainthe Calculate (Nominal) Power receive in both site.

This module is just a help pointed at those never worked on Microwave Antenna Systems and when this task isnew.

2 ALIGNMENT FUNDAMENTALS

2.1. Azimuth Location

Azimuth position errors can result from incorrect bearing marker position or inaccurate compass readings.

True North (Map) and Magnetic North (Compass).

True north on most maps is the geographic North Pole. Azimuth bearing on site maps is generally given withrespect to true north. Compasses, however, point to the magnetic North PoleIf this difference is not taking in consideration, the antenna azimuth will be incorrect.The angular difference between true north and magnetic north is called the Declination Constant. Declinationvaries from place to place.

To convert TRUE BEARING indicated on a site map, to corrected MAGNETIC BEARING read by a compassapply the following rule:

Add the declination constant to true bearing for sites EAST of the zero declination line , or subtract the declinationconstant from true bearing for sites WEST of the zero declination line.Declination constants are often given on site data sheets.

All the above mentioned data normally are reported to the Survey report documents.





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Compass Readings and Azimuth Marker Location.

Azimuth position errors can also result from inaccurate compass readings. Magnetic compasses are not reliablenear metal towers.Compass readings should be taken at least 30 mt away from metal towers (if the compass is not screenedproperly).One method o f locating an azimuth marker is to first locate a point, on true azimuth, 30 mt or more from the tower(point A in a next figure).Then locate a second point on true azimuth 30 mt away from the point A and place the azimuth marker in theground (point B in a next figure). The greater these distances are from the tower, the more accurate the azimuthposition will be.

For Azimuth marker is also possible use a stick or rope near the Tower.

TN= True NorthMN= Magnetic NorthD= Declination ConstantMA= Magnetic Azimuth

True Azimuth = 90°Equivalent Magnetic Azimuth = 94°NorthDeclination Constant = 4°

D

TNMN

MA4°

4° Flag or Stake

Ref A Ref B30 mt or more 30 mt or more

Stick or Rope

Tower





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2.2. Levelling Antenna

Another common alignment problem is improper levelling of antenna and feed. The antenna and feed must beabsolutely level. In rare instances, where extreme differences in elevation exist, such as in mountainous terrain oron tall buildings, the antenna will not be level. For normal variations in tower heights and ground elevations,levelling corrections should not be made unless exact differences are known.For example, with a level antenna, beam width at 40 Km is typically many times the height of a 76 mt tower (seenext Figure). However, if the basic level position is only half a bubble width off level, (as shown in the secondfigure), the antenna's main beam will be shifted 2 degrees, missing the adjacent tower by a 800 mt.Make attention of antenna’s levelling due to the feed attachment.

2.3. Pole fixing

In rare instances, alignment problem is caused by improper levelling (installation or project faulty) of antenna fixingpole.This is very important to check when the pole of the frame is mounted on a tower. A bad vertical position of thepole may result a wrong performance during the antennas alignment.The wrong results depend to the cross polarization effect.

Is suggested that after a visual check of antenna installation, verify (using a bubble width) the verticality ofantenna pole.To get a vertical position of the pole for all around it, it is necessary checking on all 360 degree around the pole.

1°

Example with a 6 Ghz 3 mt Antenna

40 Km

76 mtTower

Beam Width700 mt

2°

Direction of radiation

Bubble Width

Level Surfac

Feed HornFlange





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2.4. Antenna Polarization (single polarization antenna)

Important consideration for antenna Path alignment is the Antenna polarization status.In case that the polar axes aren’t levelled correctly the Microwave link will encounter a lower receive level, theproper adjustment of the antenna is not possible, since the radiation pattern are not that developed and you mayget a wrong level received.It should be the same for both sites and according with the RF planning.

For properly polarization, verify on the back side of the antenna that the polar axes are correctly.The polarization is usually specified as follows: V for vertical and H for Horizontal (with a properly mark point or alabel on the antenna feed piece).In any case refer to the installation instruction insert on the antenna’s box.

See some Flanges view (only for example)

UDR Type UBR Type

Vertical Polarization Horizontal Polarization Vertical Polarization Horizontal Polarization

See Antennas back side view (only for example)





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2.5. Antenna Polarization (double polarization antenna)

In case of double polarization horn is mandatory refer to the installation instruction. There is different type ofdouble polarization feed, any model use a different assembly and view for the output flanges.

See Antennas back side view (only for example)

Example 1

Rear view of feed hubGeneral view of feed hub Horizontal arrow > Horizontal Polarization

Vertical arrow > Vertical Polarization

Example 2

General view of feed hub(see label for polarization reference)

For the Antenna Path alignment is fundamental the feed are properly assembled and levelling.

To check the feed levelling in case of feed horn on example 1, loosen feed assembly mounting bolts. Placebubble level across feed horn in back of antenna to measure horizontal level. If necessary rotate feed assemblyuntil horizontally level. Tighten feed assembly mounting bolts.





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2.6. Radiation Pattern and Signal Strength

Antennas can be verified as being on main beam by comparing measured received signal strength with calculatedRx power level.Signal strength readings are usually measurable when at least a main beam and first side lobe are aligned. Thestrongest signal occurs at the center of the main beam.The highest first lobe signal is typically 20-25 dB less than the main beam signal. When both antennas are alignedfor maximum main beam signal strength, the PRx Level will typically between -30 to -55 dBm (depend to the hopcalculation).

If calculated Power Receive Level, matches with the measured signal strength, both antennas are aligned on mainbeam.

For example:

Typical path loss at 6 GHz for a 33 km path is about 138 dB.Typical antenna gain for a 3 mt antenna at 6 GHz is about 43 dB, or 86 dB for both site antennas.We consider Tx Power +0 dBm

+0 dBm Tx Power

-138 dB path loss

+86 dB antenna gain (2 antennas)

-52 dBm Nominal Receive Level

If the measured signal was near -52 dBm, the antennas would be aligned on main beam. If the measured signalwas only -75 dB, one antenna would be aligned on the first side lobe - not the main beam. If both antennas arealigned on the first side lobe, the receive signal would probably not be measurable.

Main beamCenter of main beam (peak radiation level)

Outer edge of main beam3 to 10 dB below the main BWM peak

Outer edge of 1st side lobe

30 db or more below the main Beam peak

First side LobeInner edge of 1 st side lobe30 dB or more below the main beam peak

Center of 1st side Lobe20 to 25 dB below the main beam peak

Head on view





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2.7. Tools and Tests inst ruments

Parabolic microwave antennas can be aligned using either a customer supplied radio, independent path alignmenttransceiver set or other properly tools and test instrument related to the equipments specifications.

The tests instruments used most of cases depend to the type and specification of the MW equipment attachedwith the parabolic Microwave antennas.

For the Siemens MW Equipment is suggested the following material:

Common Test Instruments Lists Note Qty

Personal Computer / LaptopTechnical requirement referred to the MW

system used(1 for team)

OS Used Windows 2K/ XPLCT Engine Related to the system SVR

Plug in software Related to the system SVR

Multimeters Suggested Analogic and Digital Multimeter (1 for team)

RS232 not modem PC serial cable Pin to Pin (Sub D9 Male / Sub D9 Female) (1 for team)

Compass (1 for team)

binocular (1 for team)

spirit level (1 for team)

Test Instruments Lists for Splitsystem

NoteQty

Multimeters Suggested Analogic and Digital Multimeter (1 for team)

Alignment Cable BNC / Banana (to be build in Field) (1 for team)

Test Instruments Lists for FullIndoor system

Note Qty

Power Meter Suggested with Battery (1 for team)

Power Sensor for power meter In the properly RF Frequency Range (1 for team)

Spectrum Analyzer In the properly RF Frequency Range (1 for team)

RF Cable In the properly RF Frequency Range (1 for team)

WG-Cable AdaptorIn the properly RF Frequency Range and

Flangie adaptor(1 for team)

Path alignment test instrument optional (1 for team)

Mechanical Tools Note Qty

Small Tools Case With two set on wrench (1 for team)

Installation Tools Bag (1 for each personnel)

Safety device (1 set for each personnel)

Documents support Note

LCT OMN Manual Related to the system SVR

PLUG IN SW OMN Manual Related to the system SVR

UMN Manual Related to the system SVR

System Installation Instructions Related to the system SVR

Antennas Installation Instructions Related to the properly antenna

Survey Report Related to the project specification

MW Info Link Form Related to the project specification





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2.7.1. Mechanical Tools

Is suggested use two set of wrench. Type and specification of wrench are indicating in the antenna installationinstruction.

2.7.2. Test Instruments

Power receive Measured value

To check the real power receive value is necessary measure the value with the properly test instrument (Power

meter) or with the included application SW of the equipment (if applicable).

Note that the test instruments suggested depend to the alignment method applied.

Independent path alignment transceiver set

Using one the path alignment test and installation of the associated hardware (cables, waveguide, Flange – Cable Adaptor etc.) can be facilitated to reduce excess mobilization costs. Some of the most widely used equipment forthis application are signal generators (used as the transmitter) and receive analyzers (used as the receiver).

A example of Test Instrument is The Path Align-RTM

of XL-Microwave Company.Two identical battery operated Path Align-Rs, one for each tower, are carried in their Weather-resistant InstrumentBack-packs to the antenna sites. By coax connection to the antenna, each Path Align-R drives its respectiveantenna directly...while receiving the signal from the other Path Align-R, simultaneously. During alignment, thePath Align-R provides continuous duplex voice communication over the antenna link, using the included headset,allowing the two technicians to communicate with each other (no cell phones required!). Both units indicate thereceived path loss, in dB, with 0.1 dB resolution (to -100 dB sensitivity).





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Power meter or spectrum analyzer

This type of test instruments is most used for Full Indoor type of MW equipment

These method measures direct the real Rx RF Signal (from the antenna Back RF output point or from the RxBranching group of MW equipment). In this case is used a Power Meter or Spectrum Analyzer for a directmeasure of RF Signal.

The MW equipment is used for the signal generators (used as the transmitter) and on the receive station is used aRF Power meter or the spectrum analyzer to check and analyze the received Signal.

The test instruments are connected to the main RF output of the equipment (just after the Branching Filter output).Note that if the spectrum analyzer is used for a RF Power measure; consider the reading error related to thetypical setting of the test instruments (Resolution bandwidth and Video bandwidth).

Station A

Transmitter SystemMW Link

Station B

Receive system

Model and Type of test instruments depend to the frequency band of system under test.

AGC Voltage reference

This type of method is used for most of Split type of MW equipment (eg. SRAL XD or SRA 4)

With AGC (Voltage control Signal, from the Reference Voltage point on the ODU or in the in same case on theproperly measure monitoring point on Indoor Equipment). In this case is used a Voltmeter (suitable a analogicmultimeter).

Note that (in case of AGC voltage) during the alignment it is not important to reach a specific value of voltage, butthe maximum value. The target of alignment is to seek the main lobe and verify the position of the two laterallobes (left and right).

Connect the voltmeter to the ODU BNC connector (for 1+1 systems connect to the main ODU).





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3 PATH ALIGNMENT PROCEDURE

3.1. Basic procedure

In order to apply a properly antenna alignment is important following the below steps indications.

Is suggested following this phase order (example with AGC voltage method):

• Verify the properly antenna installation

• Verify the verticality of the antenna pole

• Verify that the frequency band and the polarization is under the project specification• Verify (using a compass or with visual reference point the properly direction of the antenna (azimuth and

elevation).

• Identify (related to the antenna type and supplier) the mechanical elements for antenna adjustment.

• Connect the Voltmeter (suggested analogical instrument) to the AGC voltage point on the ODU (or othermeasure point depending to the test instruments used).

• If the MW system is with the ATPC function, disable this function in both station and set the Ptx power onthe maximum value (at the same time verify that all RF component are active and under projectspecification).

• Start the main analysis of Prx signal in station A (move in Azimuth and after elevation), search themaximum value on the Voltmeter.

• Proceed with a fine adjustment in Station A for the maximum value on the Voltmeter.

• Start the main analysis of Prx signal in station B (move in Azimuth and after elevation), search themaximum value on the Voltmeter.

• Proceed with a fine adjustment in Station B for the maximum value on the Voltmeter.• At the end verify that the Prx value are under the project specification, if not proceed with next step

• Alternative fine adjustment (alternatively in station A and B) to search the maximum value on theVoltmeter.

• At the end verify that the Prx value are under the project specification

• Close all mechanical elements (under a severity control with the Voltmeter) of the antenna.

Check if the Antennas in both sites are mounted in the correct direction. If you cannot see the opposite site use acompass but remember that it may not work properly close to a metal tower.The use of compass is only to identify a reference for the main direction, in any case is suggested adjust theantenna with the electrical reference (voltmeter).

Start the alignment operation from site A. Connect the voltmeter to the ODU BNC connector (for 1+1 systemsconnect to the main ODU).

Note the relative reference point when the operator starts the mechanical adjustment.

Sometime is suggested a Prx analysis referred to a large angle and not only using a fine adjustment method. Inthis case is suggested slacken the main bolts (1 or 2 turn) in order to move the antenna from the main attachmenton the pole. In a secondary time use the fine elements.





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3.1.1. Adjust ing the antenna

For all mechanical adjustment reference point see the documentation regarding antenna installation.

Horizontal adjustment of the antenna

Start to move slowly the azimuth at site A and observe the readings of the voltmeter in order to define the principlelobe from the two lateral lobe (in case of no signal detect apply the suggested step in the above chapter).Repeat the panning in left and right to be sure about the principal lobe and then fix the horizontal.

1 2

3 4

Note that sometime to search the main lobe is necessary open the main bo lts of antenna and not only thebolts fo r the fine adjustments.

Fine adjustment Bolts

Main fixing Bolts





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3.1.2. Vertical adjustment of antenna

Start to move slowly the elevation at site A and observe the readings of the voltmeter in order to define theprinciple lobe from the two lateral lobe (in case of no signal detect apply the suggested step in the above chapter,but for the vertical adjustment).

Repeat the scansion of elevation (up and down) to be sure about the principal lobe and then fix the vertical.

3.1.3. Fine adjustment of antenna

The vertical and Azimuth fine adjustment follows the same procedure as it did with the proceedings describedbelow but only into the maximum signal or in the main lobe of the antenna radiation.

After completing all steps fix all screw on the antenna and verify the receive level with the calculated receive level.If you within a range of project specification you have perform the job.In any case for all adjustments reference point see the antenna documentation.





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3.2. Step by step Basic

Related to the Link configuration use the following main step:

3.2.1. Standard Link (one antenna per site)

• Step 1: Move antenna Station A for max Prx value. (Azimuth and Elevation) and than fix the antenna

• Step 2: Move antenna Station B for max Prx value. (Azimuth and Elevation) and than fix the antenna

• Step 3: Fine adjustment antenna Station A for max Prx value. (Azimuth and Elevation) and than fix theantenna

• Step 4: Fine adjustment antenna Station B for max Prx value. (Azimuth and Elevation) and than fix the

antenna• Step 5: Verify the Prx value (in both station) with project specification. If the values are in the

specification fix all antennas elements. If not, repeat step 3 and 4.

3.2.2. Link in Antenna Diversity conf iguration and / or Hot Stand-By system (Two antennas persite)





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Parabolic Antennas Al ignment procedure

• Step 1: Move the main antennas in station A and B, referred to the procedure for standard alignment.

• Step 2: Verify the Prx value (in both station) with the project specification. If the values are in thespecification fix all antennas element.

• Step 3: Move the diversity antenna only in Station A with the main in station B for max Prx value(Azimuth and Elevation). Than fix the antenna (don’t move the Main Antenna in the Station B)

• Step 4: Move the diversity antenna only in Station B with the main in station A for max Prx value(Azimuth and Elevation). Than fix the antenna (don’t move the Main Antenna in the Station A)


3.2.3. Link in Antenna Diversity conf iguration and / or Freq. diversit y system (Two antennas persite)

• Step 1: Move the main antennas in station A and B, referred to the procedure for standard alignment.


• Step 3: Move the secondary antennas in station A and B, referred to the procedure for standardalignment.


• Step 5: Verify all the Prx value (in both station) with the project specification. If the values are in thespecification fix all antennas element.

Parabolic Antenna Alignment Procedure

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