Transcript
ODU Installation and Pointing Manual
DOC No:
831422
REVISION:
P3
DATE:
April 23, 2004
ODU Installation And Pointing Manual Revision P3
Document Number:
831422
Revision:
P3
Date:
April 23, 2004
Proprietary Notice:
The information contained herein is proprietary to EMS Technologies or third party proprietary information which EMS is obligated to protect and shall not be disclosed in whole or in part without the prior written permission of EMS Technologies Limited.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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TABLE OF CONTENTS
1.
INTRODUCTION 5 1.1 Scope............................................................................................................5 1.2 Introduction..................................................................................................5
2.
SAFETY INSTRUCTIONS 6 2.1 Hazards Caused By Electromagnetic Fields ................................................6 2.2 Grounding ....................................................................................................7 2.3 Power Lines..................................................................................................7 2.4 Utilities.........................................................................................................7 2.5 Assembly......................................................................................................7 2.6 Site Survey ...................................................................................................7 2.6.1 Things To Know ..................................................................................7 2.6.2 Site Survey Report ...............................................................................8
3.
GENERAL INSTALLATION INFORMATION 9 3.1 Local Lightning Protection System (LPS) ...................................................9 3.2 Cable Routing ..............................................................................................9 3.2.1 Routing the LNB and BUC Coaxial cables .........................................9 3.2.2 Attaching the Coaxial cables to the LNB and BUC.............................9
4.
ANTENNA ALIGNMENT 11 4.1 Required Equipment (typical)....................................................................11 4.2 Installation Example ..................................................................................11 4.3 Alignment Procedure .................................................................................12 4.3.1 Initial Alignment ................................................................................12 4.3.2 Fine Alignment ..................................................................................15 4.3.2.1 Antenna Line-up with Satellite Service Provider ..........................15 4.3.2.2 Antenna Line-up Carrier ................................................................15
5. APPENDIX A INSTRUCTIONS 6.
-
GENERAL
LNB
&
BUC
INSTALLATION 16
APPENDIX B - ANTENNA ASSEMBLY MANUAL
19
7. APPENDIX C - GUIDELINES FOR PROVIDING SURGE PROTECTION 20 7.1 Introduction................................................................................................20 7.2 Not Just Lightning......................................................................................21 7.3 Grounding Is Fundamental.........................................................................21 7.4 Lightning Rods...........................................................................................21 Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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7.5 Downconductors, Bonding and Shielding .................................................22 7.6 Grounding ..................................................................................................22 7.7 Summary ....................................................................................................23 7.8 Local Lightning Protection System (LPS) .................................................23 7.8.1 Local LPS available ...........................................................................23 7.8.2 Local LPS not available .....................................................................23 7.9 Grounding – Practical Examples ...............................................................23 7.9.1 Grounding the ODU – Ground Pole Installation ...............................23 7.9.2 Grounding the ODU –Non-Penetrating Roof Mount (NPRM) Installation......................................................................................................25 Figure 7-5. Typical Non-Penetrating Roof Mount Ground Connection .......27 7.9.3 Routing the IFL..................................................................................27
LIST OF TABLES TABLE 4-1. TYPICAL ANTENNA INSTALLATION / ALIGNMENT EQUIPMENT LIST ... 11 TABLE 5-1 REQUIRED LNB & BUC INSTALLATION ITEMS .................................... 16
LIST OF FIGURES FIGURE 1-1 SIT BLOCK DIAGRAM ........................................................................... 5 FIGURE 2-1 PARABOLIC ANTENNA RADIATION HAZARD AREA ............................... 6 FIGURE 4-1 EXAMPLE SATELLITE LOOK ANGLES FROM EMS MONTREAL ............. 12 FIGURE 4-2 TYPICAL BEACON SPECTRAL SIGNATURE ........................................... 14 FIGURE 4-3 TYPICAL FORWARD LINK SPECTRAL SIGNATURE ................................ 14 FIGURE 4-4 TYPICAL KU BAND VSAT SPECTRAL SIGNATURE .............................. 15 FIGURE 5-1 O-RING ON BUC FLANGE ................................................................... 17 FIGURE 5-2 O-RING ON LNB FLANGE .................................................................... 17 FIGURE 5-3 LNB, BUC AND FEED ASSEMBLY ...................................................... 18 FIGURE 7-1 DETAIL OF GROUND MOUNT POLE GROUND CONNECTION ................. 24 FIGURE 7-2 DETAIL OF GROUND MOUNT POLE GROUNDING METHOD .................. 25 FIGURE 7-3 TYPICAL NON-PENETRATING ROOF MOUNT ....................................... 26 FIGURE 7-4 DETAIL OF NON-PENETRATING ROOF MOUNT GROUND CONNECTION 26 FIGURE 7-5 TYPICAL NON-PENETRATING ROOF MOUNT GROUND CONNECTION ... 27 FIGURE 7-6 DETAIL OF IFL GROUNDING BLOCK CONNECTION .............................. 28
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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1.
INTRODUCTION
1.1
Scope This document establishes the proposed steps required in a successful installation of a Ku-Band antenna. The antenna is part of the Satellite Interactive Terminal (SIT), developed by EMS Technologies Canada Ltd.
1.2
Introduction The intended system is a star network where each user terminal inter-connects with a Hub Station to gain access to a wide variety of multimedia services via satellite. The communication between the Hub Station and the user terminal is done solely through satellite links, a Return Link (from the user terminal to the hub) and a Forward Link (from the hub to the user terminal). The Satellite Interactive Terminal (SIT) is composed of the Outdoor Unit (ODU), which includes the antenna and RF Transceiver, and the Indoor Unit (IDU). Please refer to the figure below.
Ku Ku/Ka
Transceiver
Antenna Subsystem Mechanical Subsystem
InterFacility Link
IDU
Ethernet Interface
To local private LAN or directly to Host
ODU
Figure 1-1 SIT Block Diagram
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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2.
SAFETY INSTRUCTIONS IMPORTANT: Installation of this product should be performed only by professional installer and is not recommended for consumer DIY (Do-It-Yourself) installations. Read and understand all safety and assembly/mounting instructions prior to commencing the installation.
2.1
Hazards Caused By Electromagnetic Fields When in operation or test mode, the ODU installation site must be considered an Area of Restricted Occupancy. Limit exposure time when ODU is in operation. Never place any part of the body between the main antenna and the antenna feed assembly or In line with the direction of the antenna transmission path when the ODU is in operation.
Figure 2-1 Parabolic Antenna Radiation Hazard Area
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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2.2
Grounding GROUNDING: The ODU must be grounded in strict accordance with National and Local electrical codes. This applies to all mounting configurations including polemounted units. Refer to section 7 (Appendix C) for more detail. CAUTION: Never operate the equipment without the ground conductor connected. WARNING: Locate the ODU at least 6 meters (20 feet) from all power lines.
2.3
Power Lines If any part of the ODU comes into contact with a power line call the local power company to remove it safely. Maintain a safe distance and do not touch any part of the ODU or the power line.
2.4
Utilities Prior to digging any holes or trenches, contact the local utility companies so that the location of underground power, telephone, fiber optic, cable, gas, water and/or sewer lines in the area can be determined.
2.5
Assembly Perform as much antenna assembly on the ground as possible. Do not install the antenna during periods of rain or strong winds. If the antenna or mast assembly falls during assembly, do not try to stop them - let the assemblies fall. Stay clear of the falling items.
2.6
Site Survey
2.6.1
Things To Know Before the ODU installation, the selected location must allow a clear “Line of Sight” from the dish to the satellite with absolutely NO obstructions. A good rule of thumb is there should be an “optical” path to the satellite. Remember as radio frequencies rise (like Ku or Ka band) the more the radio signal takes on aspects of light - it doesn’t bend, it gets attenuated by snow and rain and it will not pass through opaque objects like trees. When looking for obstacles that may be in the path of the signal (according to the calculated satellite look angles), take into consideration future tree growth, building renovations or additions and new construction in the area.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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Ensure that the placement of the ODU will allow the mount to be securely fastened so it will not loosen or become misaligned due to strong winds or age. The site should also be selected to safeguard the ODU from accidents and vandalism. As noted earlier, due to the potential for the ODU to create harmful RF radiation to humans, it is desirable to have the ODU in a restricted area. Warning signs should also be posted to alert personnel that have access to the area where the ODU is installed. When determining the ODU location, don’t forget to carefully plan how and where to run the IFL cables. Also, the ODU will require a proper ground system. Consideration must be given regarding access to the building, finished rooms or ceilings that must be contended with and how to get the cables to the IDU location. If roof mounted, the installer must validate with the building owner whether the roof can support the extra weight of the antenna, NPM and ballast. The proposed site should also have access to an AC power receptacle capable of 1kW that can be used temporarily during the installation process 2.6.2
Site Survey Report Make sure to record all data obtained during the survey, sketches, photographs, captures of any sort showing how clear or obstructed the “Line of Sight” is between the ODU and the satellite. Please show all these details in your report that will help decide if the site is adequate. Also include data about cable entries from and to the outdoor equipment and cable runs inside the building. Insure your report includes the measurements performed with the GPS receiver at the ODU site: Site Longitude: DMS West or East Site Latitude: DMS North or South Site Elevation: Meters or Feet above sea level Also include the city, closest street intersection and postal code. This report will help troubleshoot the SIT installation if a problem arises.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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3.
GENERAL INSTALLATION INFORMATION This guide assumes that the installer is familiar with the installation of VSAT systems and has a good working knowledge of RF equipment, grounding, alignment of parabolic antennas, the associated test equipment and installation tools.
3.1
Local Lightning Protection System (LPS) The LPS is used for grounding the ODU and IFL cables in order to insure their protection in case a lightning strikes them. Refer to section 7 (Appendix C) for more detail.
3.2
Cable Routing
3.2.1
Routing the LNB and BUC Coaxial cables Select lengths of coaxial cable that can be easily routed from the ODU to the IDU. A “through way” must be created into the building structure for these cables. It may be helpful to identify the cables at both ends with TX for transmit and RX for receive. Form a 3” to 5” drip loop in the cables before inserting them through the access hole(s). Secure the drip loop and cables. Using silicone sealant or equivalent, seal the cable entry into the building, It is recommended that the F connectors be installed after the IFL cables have been pulled and fastened. Inside the building, route the cables to the IDU location. This may require routing the cables through crawl spaces, utility rooms, walls or attics. The cables should be routed directly to the rear of the IDU without unnecessary splices and most importantly, respecting the minimum bend radius. Keep the cables away from sources of high RF field strengths (microwave ovens) and heat.
3.2.2
Attaching the Coaxial cables to the LNB and BUC At the ODU, route the two coaxial cables (for BUC and LNB) along the outside of the pole mount. Use cable ties to secure the cables together. Allow for some slack in the cables should you need to remove them from the LNB or BUC later. Note: These following steps are to be completed AFTER antenna alignment When attaching the cable connectors on to the LNB and BUC, insure only the outer rotating nut of the connector is turned. The cable and the main body of the connectors must NOT rotate or twist. Damage to the connector or cable may occur if the main body of the connector is rotated. Torque connectors to 20 in-lbs. (2.25 N·m) maximum. See Appendix A for details on assembling the LNB & BUC to the antenna feed.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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Using a short piece of rubber tape, wrap the Tx cable connection such that both the external thread of the female portion of the BUC connector and the complete cable connector are completely covered by the tape. Start on the cable and work toward the BUC. Start and end with one full overlap of the tape. This will ensure a weatherproof connection. Repeat this step for the LNB cable connection.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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4.
ANTENNA ALIGNMENT
4.1
Required Equipment (typical)
75ohm IFL RG-6 Coaxial Cables Compass for azimuth measurements Inclinometer for elevation measurements Level for surfaces Digital Multimeter GPS receiver to measure XYZ position Analyzer: · FELEC MC10-SAT or equivalent Or · Spectrum analyzer with - up to 2.15 GHz span (Forward Link) - down to -80dBm (Noise Floor) And · 2-way splitter with DC bypass, adapters Cell phone to call the satellite operator (NOC) Laptop to setup IDU and antenna line up with the satellite operator Ethernet “cross-over” cable to connect the IDU to the laptop Proper hardware to attach the mount to the building Grounding materials (may be provided by ODU assembly kit) UV Resistant Cable ties UV Resistant Rubber or Electricians tape for connector sealing Set of installation tools Table 4-1 Typical Antenna Installation / Alignment Equipment List 4.2
Installation Example The following example uses a typical VSAT satellite and a SIT located at the EMS Montreal facility. This is ONLY an example – YOUR SPECIFIC INSTALLATION WILL BE DIFFERENT! Step 1. With a GPS receiver measure the geographic position of the site (at the ODU) “XYZ” or Longitude (DMS) & Latitude (DMS) and Elevation (meters above sea level). Record this information. Step 2. Determine the satellite look angles. This usually can be accomplished by downloading a look-angle calculator utility from the satellite operator’s website. In our example, the satellite is located at 93° West Longitude and the Montreal EMS location is 45.423055° North by 73.925833° West.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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Step 3. Once you have determined the azimuth and elevation information, go back to the proposed ODU installation site and using the compass and inclinometer, determine the location of the satellite in the sky. Note there is a Magnetic Declination that must be known for proper compass bearings. Use this number when sighting the azimuth angle for the satellite. If there are no obstructions from (trees, buildings, etc) to the satellite, then the proposed ODU location might be a possible candidate. Other factors such as TI, cable runs, and the site security also should be considered before any final decision is made. Scanning for TI is beyond the scope of this installation manual. Step 4. Once all the above parameters are known and dish location is selected the antenna can be assembled and installed using the assembly & installation manual that accompanies the antenna. This manual will describe in detail the required mechanical mounting for the specific antenna for various environmental conditions. Once the antenna assembly and installation are complete it then can be aligned to the satellite.
Figure 4-1 Example Satellite Look Angles from EMS Montreal 4.3
Alignment Procedure
4.3.1
Initial Alignment The installation uses a FELEC MC10-SAT Analyzer (www.felec.com). Equivalent equipment or a spectrum analyzer using a splitter with DC by-pass can be used.
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This procedure assumes the mounting mast for the antenna is level in all planes. This is extremely important for alignment ease. Loosen the Feed/LNB assembly and roughly set the polarization as per the calculated values. This is a good starting point. Finger-tighten the feed to allow rotation of the Feed/LNB assembly for fine tuning later. Connect the LNB to the analyzer using a short piece of RG-6 coaxial cable. Set the analyzer center frequency to receive either a beacon signal (Figure 4-2), a forward link (Figure 4-3) or a wideband (550 MHz) satellite spectrum similar to Figure 4-4. These plots were derived using our installation example – remember your installation will be different from what is seen in these plots. Set the antenna elevation angle. Don’t forget to take the antenna-offset angle into account when setting the elevation! The offset angle value can be found in the antenna installation manual. After the elevation has been set, move the antenna in azimuth while observing the analyzer. Position the antenna to receive the maximum strength of the signal and quality readings. Verify that the antenna is not pointed on a sidelobe. In order to verify the antenna is aligned on the main beam, slowly move the antenna 5° in azimuth each direction. If the signal is acquired at the three positions, align the antenna to the middle position. Note the sidelobes may not be detectable, in that case, use the only position where the received signal strength is maximum. Repeat this step for both azimuth and elevation. After rough alignment, switch to the analyzer to fine amplitude resolution (2 dB/division) and re-adjust the azimuth and elevation. Repeat until no improvement is seen. Note the azimuth and elevation adjustments may exhibit some interaction. Temporarily lock down the alignment adjustment hardware. At this point the azimuth and elevation have been set, but the polarity still must be aligned. Disconnect the analyzer from the LNB output port. Connect the IFL cables to the ODU, which should have been previously installed. Insure the cables are connected to the correct ports, Rx to Rx and Tx to Tx. Make note of which cable leads to the LNB and which to the BUC. It may be helpful to mark the cables at the ends with tape labeled with the component it leads to (either the LNB or BUC). NOTE: Damage to the LNB, BUC and IDU may occur if the coaxial cables are reversed.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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Figure 4-2 Typical Beacon Spectral Signature
Figure 4-3 Typical Forward Link Spectral Signature
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Figure 4-4 Typical Ku Band VSAT Spectral Signature 4.3.2
Fine Alignment
4.3.2.1
Antenna Line-up with Satellite Service Provider Make sure to have all information at hand before calling the Satellite Service Provider. Contact the Satellite Service Provider at which point you will interface with one of the operators at the NOC and must follow their instructions in order to perform a “peak & pol”. The operator will ask you to transmit a CW (unmodulated tone) in order to align the antenna for azimuth, elevation and now polarity. Let the operator know what adjustments are being made and they will provide feedback on the signal level. Do the polarity adjustment last. Remember; avoid placing body parts in front of the reflector while transmitting.
4.3.2.2
Antenna Line-up Carrier This is the carrier (frequency test slot) to be used with CW tone generated from the IDU. This command can be sent from the IDU “Installer page”. Once The Satellite Service Provider is satisfied with your line-up you should tighten all the adjust hardware. To access the test commands settings go to “Test Control” page. In this page you will be able to set the frequency and adjust the power level of your CW signal as per the Satellite Service Provider’s request. Please consult the IDU Installation Manual for detailed IDU information.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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5.
APPENDIX A INSTRUCTIONS Item 1 2 3 4
GENERAL
LNB
&
BUC
INSTALLATION
Description BUC + mounting hardware + O-ring LNB + mounting hardware + O-ring Screwdriver(s), adjustable wrench, HEX keys Electrical or rubber tape
QTY 1 1 Misc. Misc.
Table 5-1 Required LNB & BUC Installation Items Note: For optimum antenna performance, the Feed Assembly should be assembled indoors in a low-humidity, clean environment. The assembled feed then can be mounted onto the antenna as a complete unit. 1. Assemble the mount, reflector, boom and feed assembly as per the manufacturer’s instructions (included with the antenna). Unpack the LNB & BUC being careful not to lose any of the hardware or damage the O-rings. 2. Note the groove on the BUC Ku waveguide flange where the O-ring must be installed. Make sure the O-ring is well seated in the groove (See Figure 1). Install the BUC onto the transmit port of the OMT (the port WITHOUT the filter) using the hardware supplied with the BUC. Make sure the ports are aligned correctly. Tighten the hardware to 24 in-lbs. (2.5 N·m) of torque. (See Figure 3). 3. Note there is also a groove on the LNB Ku waveguide flange where the O-ring must be installed. Make sure the O-ring is well seated in the groove (See Figure 2). Install the LNB onto the receive port of the OMT (the port WITH the filter) using the hardware supplied with the LNB. Make sure the ports are aligned correctly. Tighten the hardware to 24 in-lbs. (2.5 N·m) of torque. (See Figure 3). 4. Once the LNB & BUC are installed, the IFL cables may be attached and tightened to 20 in-lbs. (2.25 N·m) of torque. Using the electrical tape (item 4), wrap the connectors from the LNB or BUC down the cable 2 inches (5cm) to insure a waterproof connection. Secure the cables along the boom to the back of the antenna with tie-raps.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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Figure 5-1 O-Ring on BUC flange
Figure 5-2 O-Ring on LNB flange
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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Figure 5-3 LNB, BUC and Feed Assembly
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6.
APPENDIX B - ANTENNA ASSEMBLY MANUAL Please refer to installation manual supplied with the antenna.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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7.
APPENDIX C - GUIDELINES FOR PROVIDING SURGE PROTECTION
7.1
Introduction The following excerpts are from documents published on the National Lightning Safety Institute website Damage from electrical transients, or surges, is one of the leading causes of electrical equipment failure. An electrical transient is a short duration, highenergy impulse that is imparted on the normal electrical power system whenever there is a sudden change in the electrical circuit. They can originate from a variety of sources, both internal and external to a facility. Lightning is a capricious, random and unpredictable event. Its' physical characteristics include current levels sometimes in excess of 400 kA, temperatures to 50,000 degrees F., and speeds approaching one third the speed of light. Globally, some 2000 on-going thunderstorms cause about 100 lightning strikes to earth each second. USA insurance company information shows one homeowner's damage claim for every 57 lightning strikes. Data about commercial, government, and industrial lightning-caused losses is not available. Annually in the USA lightning causes more than 26,000 fires with damage to property (NLSI estimates) in excess of $5-6 billion. The phenomenology of lightning strikes to earth, as presently understood, follows an approximate behavior: 1.
The downward Leaders from a thundercloud pulse towards earth seeking out active electrical ground targets.
2.
Ground-based objects (fences, trees, blades of grass, corners of buildings, people, lightning rods, etc., etc.) emit varying degrees of electric activity during this event. Upward Streamers are launched from some of these objects. A few tens of meters off the ground, a "collection zone" is established according to the intensified local electrical field.
3.
Some Leader(s) likely will connect with some Streamer(s). Then, the "switch" is closed and the current flows. We see lightning.
Lightning effects can be direct and/or indirect. Direct effects are from resistive (Ohmic) heating, arcing and burning. Indirect effects are more probable. They include capacitive, inductive and magnetic behavior. Lightning "prevention" or "protection" (in an absolute sense) is impossible. A diminution of its consequences, together with incremental safety improvements, can be obtained by the use of a holistic or systematic hazard mitigation approach, described below in generic terms.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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7.2
Not Just Lightning The most obvious source is from lightning, but surges can also come from normal utility switching operations, or unintentional grounding of electrical conductors (such as when an overhead power line falls to the ground). Surges may even come from within a building or facility from such things as fax machines, copiers, air conditioners, elevators, motors/pumps, or arc welders, to name a few. In each case, the normal electric circuit is suddenly exposed to a large dose of energy that can adversely affect the equipment being supplied power. The following is a guideline on how to protect electrical equipment from the devastating effects of high-energy surges. Surge protection that is properly sized and installed is highly successful in preventing equipment damage, especially for sensitive electronic equipment found in most equipment today.
7.3
Grounding Is Fundamental A surge protection device (SPD), also known as a transient voltage surge suppressor (TVSS), is designed to divert high-current surges to ground and bypass your equipment, thereby limiting the voltage that is impressed on the equipment. For this reason, it is critical that your facility have a good, low-resistance grounding system, with a single ground reference point to which the grounds of all building systems are connected. Without a proper grounding system, there is no way to protect against surges. Consult with a licensed electrician to ensure that your electrical distribution system is grounded in accordance with the National Electric Code (NFPA 70).
7.4
Lightning Rods In Franklin's day, lightning rods conducted current away from buildings to earth. Lightning rods, now known as air terminals, are believed to send Streamers upward at varying distances and times according to shape, height and other factors. Different designs of air terminals may be employed according to different protection requirements. For example, the utility industry prefers overhead shielding wires for electrical substations. In some cases, no use whatsoever of air terminals is appropriate (example: munitions bunkers). Air terminals do not provide for safety to modern electronics within structures. Air terminal design may alter Streamer behavior. In equivalent e-fields, a blunt pointed rod is seen to behave differently than a sharp pointed rod. Faraday Cage and overhead shield designs produce yet other effects. Air terminal design and performance is a controversial and unresolved issue. Commercial claims of the "elimination" of lightning deserve a skeptical reception. Further research and testing is on-going in order to understand more fully the behavior of various air terminals.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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7.5
Downconductors, Bonding and Shielding Downconductors should be installed in a safe manner through a known route, outside of the structure. They should not be painted, since this will increase impedance. Gradual bends (minimum 8 inch (~20cm) radius) should be adopted to avoid flashover problems. Building steel may be used in place of downconductors where practical as a beneficial part of the earth electrode subsystem. Bonding assures that all metal masses are at the same electrical potential. All metallic conductors entering structures (AC power, gas and water pipes, signal lines, HVAC ducting, conduits, railroad tracks, overhead bridge cranes, etc.) should be integrated electrically to the earth electrode subsystem. Connector bonding should be thermal, not mechanical. Mechanical bonds are subject to corrosion and physical damage. Frequent inspection and Ohmic resistance measuring of compression and mechanical connectors is recommended. Shielding is an additional line of defense against induced effects. It prevents the higher frequency electromagnetic noise from interfering with the desired signal. It is accomplished by isolation of the signal wires from the source of noise.
7.6
Grounding The grounding system must address low earth impedance as well as low resistance. A spectral study of lightning's typical impulse reveals both a high and low frequency content. The high frequency is associated with an extremely fast rising "front" on the order of 10 microseconds to peak current. The lower frequency component resides in the long, high energy "tail" or follow-on current in the impulse. The grounding system appears to the lightning impulse as a transmission line where wave propagation theory applies. A single point grounding system is achieved when all equipment within the structure(s) are connected to a master bus bar which in turn is bonded to the external grounding system at one point only. Earth loops and differential rise times must be avoided. The grounding system should be designed to reduce ac impedance and dc resistance. The shape and dimension of the earth termination system is more important a specific value of the earth electrode. The use of counterpoise or "crow's foot" radial techniques can lower impedance as they allow lightning energy to diverge as each buried conductor shares voltage gradients. Ground rings around structures are useful. They should be connected to the facility ground. Exothermic (welded) connectors are recommended in all circumstances. Cathodic reactance should be considered during the site analysis phase. Manmade earth additives and backfills are useful in difficult soils circumstances: they should be considered on a case-by-case basis where lowering grounding impedances are difficult an/or expensive by traditional means. Regular physical
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inspections and testing should be a part of an established preventive maintenance program. 7.7
Summary It is important that all of the above subjects be considered in a lightning safety analysis. There is no Utopia in lightning protection. Lightning may ignore every conceivable defense. A systematic hazard mitigation approach to lightning safety is a prudent course of action. The preceding excerpts were from documents published on the National Lightning Safety Institute website
7.8
Local Lightning Protection System (LPS)
7.8.1
Local LPS available If the ODU is installed at a site where the local LPS (Lightning Protection System) of the building is readily accessible the copper ground wire should be connected to this LPS in strict accordance with National and Local electrical codes.
7.8.2
Local LPS not available Proper grounding provision where a local LPS not accessible requires installation of a ground rod or ground rod system. The ground wires from the ODU would connect to this ground system. Route the ground wires from the antenna-structure grounding-bolt to the ground rods. Use a ground rod clamp to attach the ground wires to the ground rod. Secure the ground wires to the ground rod and the antenna mounting structure to avoid physical damage. In sure all ground connections are secured. Note: Ground wire size and rod installation must strictly adhere to the National and Local electrical codes.
7.9
Grounding – Practical Examples
7.9.1
Grounding the ODU – Ground Pole Installation In general, there are two types of ODU antenna mounts, roof and ground mounts. The ground mounting typically use a pipe which is inserted into an appropriate sized hole filled with concrete. As shown in Figure 7-1, make the connection to the mounting pole and route the ground wire to the ground rod. Use a ground rod clamp to attach the ground wire to the ground rod. Secure & protect the ground wire from physical damage.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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Figure 7-1 Detail of Ground Mount Pole Ground Connection
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Figure 7-2 Detail of Ground Mount Pole Grounding Method 7.9.2
Grounding the ODU –Non-Penetrating Roof Mount (NPRM) Installation Roof mounting ODUs typically use a non-penetrating mount held in place with concrete blocks. See Figure 7-3 for the mount diagram. Referring to Figure 7-4, make the ground connection to the NPRM frame. Route the copper ground wire “a” to the LPS or to the ground rod. Use a ground rod clamp to attach the ground wire to the ground rod as in Figure 7-2. Secure, protect the ground wire from physical damage. If necessary, label the ground wire.
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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Figure 7-3 Typical Non-Penetrating Roof Mount
Figure 7-4 Detail of Non-Penetrating Roof Mount Ground Connection
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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Figure 7-5 Typical Non-Penetrating Roof Mount Ground Connection 7.9.3
Routing the IFL An important goal of your cable installation is to protect the cables from physical damage and moisture penetration. To protect the cables from physical damage, secure them to walls or other stable surfaces with the appropriate hardware. This prevents the cables from sagging and being damaged by people stepping on or running over them with equipment. Prevent moisture penetration by using weatherproof connectors, and by sealing any connection that is exposed to the elements. Drip loops provide a connection with additional protection by preventing moisture from traveling down the cables and entering the connection. Select lengths of coaxial cable that can be easily routed from the ODU to the grounding block. Form a 3” to 5” drip loop in the cables before the grounding block as shown in Figure 7-6. From the grounding block, continue the IFL run into the premises to the IDU. Run the ground wire (“a” in Figure 7-6) from the ODU mount and connect it to the grounding block then on to the ground rod system. Make sure all ground clamp connections are secure, both on the antenna mount and grounding block(s).
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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Figure 7-6 Detail of IFL Grounding Block Connection
Use or disclosure of information contained herein is subject to the restriction on the title/cover page.
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