Tilt and Azimuth Methodology

Specification number December 2005 Iran WI/01/2006 CONFIDENTIAL Issue 1 Rev 1

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TILT AND AZIMUTH METHODOLOGY 17. Tool Requirements

a. 1 : 50 000 map or a known waypoint with bearings to the site in question.

b. Azimuth Aligning tool

c. G.P.S (Minimum specification equivalent to Magellan 315)

d. Electronic tilt meter NOTE: No Compass may be used to align antennas. Compasses may not be used on any site and no exceptions may be made.

18. USING GPS TO SET AZIMUTHS

When a Greenfield site-build has a lattice mast, it is always a good idea to have one face of the mast structure facing in a particular direction. Also, once panel antennas have been mounted, they need to be rotated to point in the correct direction. This applies to rooftop sites as well.

At present, the BTS Site build Specification states that one face of a lattice mast must be facing North, which is not always ideal (for example, when a road-site covers an East-West road). Actually, it is up to the Planner of that site to say which direction he considers best.

COMPASS DIRECTIONS

The compass is based on a circle of 360 degrees, with North being zero (and also 360) degrees.

N

S

EW

030

60

90

120

150180

210

240

270

300

330

The direction in which an antenna points is known as its "azimuth". An azimuth is always defined with respect to True North, so that a panel (located at "X") which is pointing East, is said to have an azimuth of 90 degrees.

Since any rotation in a clockwise direction will increase the azimuth, a rotation in the clockwise direction is known as a "positive" or "+" rotation. For example, to go from 120 to 150 needs a rotation of +30, that is to say a rotation of 30 in the clockwise direction.


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Similarly, an anti-clockwise rotation is known as "negative" or "-" rotation. LONGITUDE AND LATITUDE

One of the methods of defining a position on the Earth is by using a set of numbers called Latitude and Longitude. If we think of the Earth as a sphere spinning around it's North-South axis, then the Equator is defined as having Latitude 0, the North Pole has Latitude 90 North and the South Pole has Latitude 90 South. The further away from the Equator the larger the number of degrees of Latitude (either North or South). For example, Johannesburg has a Latitude of about 26 South while Paris is about 49 North.

In the same way that Latitude shows how far North or South of the Equator one is, so Longitude shows how far East or West one is from a reference line drawn from the North Pole, through an otherwise undistinguished little village called Greenwich in England, and down to the South Pole. Cape Town is about 18 East of this line and New York is about 74 West.

To get greater accuracy, each Degree is divided into 60 Minutes (which has very little to do with the 60-minutes-in-an-hour that everyone is used to) and each Minute is divided into 60 Seconds (same comment as before). Note that a position which is defined in terms of Degrees, Minutes and Seconds is less accurate than one which is defined in terms of Degrees, Minutes and thousandths of a Minute (precise to 1/60Minute versus precise to 1/1000Minute).

The exact definition of Latitude and Longitude was initially done with each country defining their own local starting point and measuring from there. South Africa used Port Elizabeth as a starting point and this gave birth to the "Cape Datum". Virtually all South African maps presently in use are based on the Cape datum.

In 1984, a unified survey was carried out which is known as the "World Geodetic System", also known as "WGS84". South Africa officially switched to this system on 1 January 1999. The difference between the two systems works out to be about 120 - 160 metres, depending on where you are.

It is possible to convert a Lat/Lon position in one system to the Lat/Lon position in the other system quite easily. Bear in mind that any specification of Latitude and Longitude should state whether Cape or WGS84 datum was used.

THE "GLOBAL POSITIONING SYSTEM" (GPS)

The GPS uses timing signals sent from a network of satellites to locate the position of a GPS receiver .

To see how this works, consider the example of a mobile phone cal, where there is an indication of the Timing Advance sent out by the base station. The timing advance shows how far the mobile is from the base station, with each Timing Advance (TA) value of 2 representing 1,1Km. A TA of 16 will mean 8,8Km while a TA of 17 will correspond to 9,35Km. Since the error between two readings is 0,55Km we can say that a given TA will place us somewhere in a "doughnut" area which is 0,55Km wide and has a radius of (TA x 1,1)/2.


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0.55km

TA 16

TA 17

All we know is that we must be somewhere in the ring, but we have no way of knowing exactly where.

If we now log onto another base station, we will get another TA that will place us in another doughnut area. If we know where these base stations are physically located, we can start to figure out where we are. We can only be in one of the two common shaded areas shown below.

If we now get a third base station, we can figure out which one of the two possible areas we are in.


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The same principle is used by GPS. Obviously the more satellites that can be seen by the receiver, the better the accuracy.

SETTING UP THE GPS RECEIVER

The following instructions apply to the Magellan 315 GPS receiver. The settings shown are highly individual and it is strongly advised that you read the manual.

Press PWR and then ENTER (within 5 seconds).

The dark area right at the top of the screen contains writing that will tell you which "Screen" you are looking at. The cursor is moved UP or DOWN, LEFT or RIGHT with the central "arrow" key. When you have the selection you want, press ENTER.

If you are using the GPS for the first time, you will get the "Initialise" screen. Press ENTER. Select Region "Africa" (ENTER) and select "South Af." (ENTER). To ignore "Elevation" selection, simply press "Enter". The next item is "Time" followed by "Date". Set defaults for a primary usage of "Land".

Use "Menu" button to open Menu and select "Setup". "Initialise" should have been already carried out; Arrow DOWN to Nav Screens; ENTER. Settings as follows :

NAV1 OFF ENTER

COMPASS OFF ENTER

NAV2 OFF ENTER

PLOT OFF ENTER

ROAD OFF ENTER

SPEED OFF ENTER

TIME OFF ENTER


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This will bring you back to the "Setup" screen with "Coord system" highlighted. ENTER and select "Primary"; ENTER. Select "Lat/Lon"; ENTER. Select "Deg/Min.MMM"; ENTER.

On "Map Datum", select "Primary"; ENTER, WGS84 (or CAPE if you absolutely haver to); ENTER.

"Elev Mode"; ENTER;"3D"; ENTER.

"Time format";ENTER; "Local 24hr"; ENTER. Set the time, one digit at a time; ENTER.

"Nav units";ENTER;" Km/Kph"; ENTER.

"North Ref"; ENTER; "True"; ENTER.

"Light timer"; ENTER; "15 secs": ENTER.

"Beeper"; ENTER; "Off"; ENTER.

"Personalize"; ENTER; "Off"; ENTER.

"Clear memory"; arrow DOWN.

"NMEA"; ENTER; "V2.1 GSA"; ENTER.

"Baud rate"; ENTER; "4800 Baud"; ENTER.

"Simulate"; QUIT.

These settings create a very boring set-up and only 2 screens will be shown, "Status" and "Position". You can toggle between the two screens by pressing the "NAV" key. "Status" shows the satellites you are seeing and their relative signal strengths. "Position" shows:

Latitude (degrees and minutes South)

Longitude (degrees and minutes East)

Elevation in metres (not very accurate)

Time

Date

Speed

Distance travelled

Heading

Compass

If you are standing still, and are locked onto satellites, you will get an "Averaging" display between "Time" and "Date", which will also show you for how many minutes the position averaging has been taking place. The longer the averaging period, the more accurate the Longitude and Latitude will be. As soon as you start to move, the "Averaging" display vanishes.

According to the local Magellan representative, it can take up to 25 minutes from switch-on for the ephemeris to be updated. It is suggested that the GPS be switched on (using vehicle cigarette-lighter power) AND BE ALLOWED TO LOG-ON when you first get into your


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vehicle; thereafter leave it on the dashboard with a clear (!) view of the sky until you get to site.

Preliminary tests show that after 25 minutes, a position repeatable to about 2 metres can be achieved. After 1 minute, the inaccuracy appears to be about 20 metres.

GREENFIELD DIRECTION-FINDING

The first requirement of direction-finding is to set up a "Baseline". This is a line between two points that goes in a known direction. These points could be, for example, the centre-point of the mast foundation (X) and an obvious landmark or landmark (Y) which could be a tree, a lamp-pole, the corner of a building or anything which is visible and is not going to move away. Do not use horses, trucks or people as a landmark.

Y Y

North - South Baseline at +45deg.Baseline to North

X X

It is often impossible to get a landmark that is exactly in the direction that you are interested in. This doesn't really matter; just choose one that is:

More-or-less in the direction that you want to point to;

Accessible (ideally next to a road that you can drive along);

Readily identifiable (an isolated tree may turn out to be part of a forest when you get close to it);

As far away as practicable. A positioning error of 20 metres in a landmark 100 metres away will give an angular error of 11,3. The same 20 metre positional error over a 1000 metre distance will give an angular error of only 1,1.

As soon as you get to site, place the GPS where the centre of the mast base is going to be and display the "Position" screen. Just leave it there while you survey the area, search for possible landmarks etc. etc. etc. The longer you leave it averaging the position, the more accurate the reading will be.

When you are ready, press the "Mark" key once. You will get a "Mark" screen with LMK001 (or some other number) highlighted at the top of the screen. Press ENTER which will allow you to name this position (say NWLNDS or whatever the site name may be, up to 6 letters long).


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LMK001 will disappear and all that will be left is a dark square. Use Arrow UP to step through the alphabet until you get to the first letter you want. Use Arrow RIGHT to get to the 2nd letter of the site-name, and so on until you've got 6 letters (or numbers). Use Arrow DOWN to step through everything until "Save LMK" is highlighted. Press ENTER. This location's latitude and longitude is now stored under the site-name.

Without switching off the GPS, take it to the previously identified distant landmark. Once there, allow the GPS to "Average" for at least 2 minutes. Then press "GO TO" which brings up the small "Go To" screen. Use Arrow DOWN to highlight "USER" and press ENTER. The list of all stored locations will appear, arranged in order of their distance from your present location.

Select the site being surveyed ("NWLNDS") by means of the Arrow DOWN. Whichever site is highlighted will have the bearing BRG and distance DST immediately displayed at the bottom of the screen. This bearing is the compass direction from the landmark to the site and therefore the bearing from the site to this point will be 180 from BRG.

If BRG is less than 180, then the bearing from the site to the landmark will be: BRG + 180.

Bearing from site to Oak Tree = BRG + 180 = 118 + 180 = 298

BRG =298

BRG =118

If BRG is 180 or more, then the bearing from the site to the landmark will be: BRG - 180.

Bearing from site to Oak Tree = BRG - 180 = 242 - 180 = 62

BRG =

62

BRG =

242


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For example, say that you need to find east. If you know that the tree is located at an azimuth of 62, a dumpy level located at mast-centre can be pointed towards the tree and then rotated +28 to point East (90).

It's not even necessary to set up the dumpy level so that the scale reads exactly 62 when it's pointed towards the tree. Just take a reading of whatever the scale shows when pointing towards the tree, and then check the scale while rotating the dumpy-level through +28 (clockwise). The dumpy level is then pointing east and you can send someone from your vast team of assistants to plant a peg in line with the cross hairs.

USING THE "TASCO" TELESCOPIC SIGHT

A similar, but slightly different, approach to the above is needed when using the "Tasco" sight to set panel azimuths.

First of all, note that with the "Tasco" sight pointing straight ahead in the same direction as the panel, the reading on the protractor will be either 0 or 180, depending on whether the sight is mounted to the left or to the right of the panel, and whether the protractor markings are facing up or down.

Because of this, it 's usually easier to simply count-off the angle that needs to be set, rather than trying to do the necessary arithmetic.

Method 1: One person all-alone.

Set up the GPS to get an average reading while you climb the mast.

From the top of the mast, select landmarks that are reasonably aligned to each direction required (for example, 0, 120 and 240). Try to get each landmark accessible, recognisable and reasonably far away (more than 500m).

Climb down the mast and set a "mark" on the GPS, which will be called "SITENAME" (6 letters maximum, so let's call it "SITNAM").

Put the GPS on your dashboard while you drive to the first landmark, which we assume will be for sector A. When you get there, let the GPS have a clear and stationary view of the sky for at least 2 minutes.

Press "GO TO", select "USER" and then select "SITNAM". The bearing (BRG) will be shown at the bottom of the screen, which we will call BRG (A). Write this down.

Put the GPS back onto the dashboard while you drive to landmark B and C. Following the same procedure as above, obtain BRG (B) and BRG (C). Switch the GPS off.

Return to the site and climb the mast again, taking the "Tasco" sight with you. Suction the sight to the back of the panel, adjust the protractor (as shown in the examples below) and rotate the panel until the cross hairs line up with each landmark in turn. Secure the panel (and check the tilt).

EXAMPLE 1: BRG (A) = 198. Azimuth of landmark = 198 - 180 = 18


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18 198

Site

Site

Landmark ALandmark A

Starting with the sight pointing straight ahead (protractor marking on either 0 or 180), rotate the sight clockwise by 18. If the panel is facing exactly North, the sight should now be pointing towards the landmark. If you don't see the landmark in the sight, rotate the panel until you do.

EXAMPLE 2: BRG (A) = 156. Azimuth of landmark = 180 + 156 = 336 = -24

156

Site

Landmark A 24

Site

Landmark A

Starting with the sight pointing straight ahead (protractor marking on either 0 or 180), rotate the sight anti-clockwise by 24. If the panel is facing exactly north, the sight should now be pointing towards the landmark. If you don't see the landmark in the sight, rotate the panel until you do.

EXAMPLE 3: BRG (B) = 289. Azimuth of landmark = 289 - 180 = 109.


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Site

Landmark B

Site

289

109

Landmark B

11

Aziomuth of 120

Starting with the sight pointing straight ahead (protractor marking on either 0 or 180), rotate the sight clockwise by 11. If the panel is facing exactly 120, the sight should now be pointing towards the landmark. If you don't see the landmark in the sight, rotate the panel until you do.

Method 2: Two people, cell-phone coverage, beautiful weather.

This is the easy way to do the job. Take a GPS reading of the site and store as before. One person climbs the mast while the other takes the GPS in the vehicle. The mast-person uses a cell-phone to guide the vehicle-person to easily identifiable landmarks. The vehicle person does the "GO TO" function from each landmark and the mast-person adjusts the panels as before.

Tilt and Azimuth Methodology

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