UBS Axcera 325A 500-Watt VHF Low-band Television Transmitter User Manual Chapter 4

UBS-Axcera 500-Watt VHF Low-band Television Transmitter Chapter 4

Chapter 4

500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures325A, Rev. 0 4-1Chapter 4Installation and Setup ProceduresThere are special considerations thatneed to be taken into account before the325A can be installed. For example, if theinstallation is completed during coolweather, a heat-related problem may notsurface for many months, suddenlyappearing during the heat of summer.This section provides planninginformation for the installation and set upof the transmitter.4.1 Site ConsiderationsThe transmitter requires an AC input lineof 220 VAC with a rating of 40 amps forthe exciter/amplifier cabinet. Make surethat the proposed site for the transmitterhas the necessary voltage requirements.The 325A is designed and built to providelong life with a minimum of maintenance.The environment in which it is placed isimportant and certain precautions mustbe taken. The three greatest dangers tothe transmitter are heat, dirt, andmoisture. Heat is usually the greatestproblem, followed by dirt, and thenmoisture. Over-temperature can causeheat-related problems such as thermalrunaway and component failure. Eachamplifier tray in the transmitter containsa thermal interlock protection circuit thatwill shut down that tray until thetemperature drops to an acceptable level.A suitable environment for thetransmitter can enhance the overallperformance and reliability of thetransmitter and maximize revenues byminimizing down time. A properlydesigned facility will have an adequatesupply of cool, clean air, free of airborneparticulates of any kind, and noexcessive humidity. An ideal environmentwill require temperature in the range of40° F to 70° F throughout the year,reasonably low humidity, and a dust-freeroom. It should be noted that this israrely if ever attainable in the real world.However, the closer the environment isto this design, the greater the operatingcapacity of the transmitter.The fans and blowers designed and builtinto the transmitter will remove the heatfrom within the trays, but additionalmeans are required for removing thisheat from the building. To achieve this, afew issues need to be resolved. The firststep is to determine the amount of heatto be removed from the transmitterroom. There are generally three sourcesof heat that must be considered. The firstand most obvious is the heat from thetransmitter itself. This can be determinedby subtracting the average power to theantenna (350 watts) from the AC inputpower (3500 watts). This number inwatts (3150) is then multiplied by 3.41,which gives 10,741, the BTUs to beremoved every hour. 12,000 BTUs perhour equals one ton, so a 1-ton airconditioner will cool a 500-watttransmitter.The second source of heat is otherequipment in the same room. Thisnumber is calculated in the same way asthe equation for BTUs. The third sourceof heat is equally obvious but not assimple to calculate. This is the heatcoming through the walls, roof, andwindows on a hot summer day. Unlessthe underside is exposed, the floor isusually not a problem. Determining thisnumber is usually best left up to aqualified HVAC technician. There are fartoo many variables to even estimate thisnumber without reviewing the detaileddrawings of the site that show all of theconstruction details. The sum of thesethree sources is the bulk of the heat thatmust be removed. There may be othersources of heat, such as personnel, andall should be taken into account.Now that the amount of heat that mustbe removed is known, the next step is to
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures325A, Rev. 0 4-2determine how to accomplish this. Theoptions are air conditioning, ventilation,or a combination of the two. Airconditioning is always the preferredmethod and is the only way to createanything close to an ideal environment.Ventilation will work quite well if theambient air temperature is below 100° F,or about 38° C, and the humidity is keptat a reasonable level. In addition, the airstream must be adequately filtered toensure that no airborne particulates ofany kind will be carried into thetransmitter. The combination of airconditioning for summer and ventilationduring the cooler months is acceptablewhen the proper cooling cannot beobtained through the use of ventilationalone and using air conditioningthroughout the year is not feasible.Caution: The use of air conditioningand ventilation simultaneously is notrecommended. This can causecondensation in transmitters. Fortube type transmitters, this can beespecially serious if thecondensation forms in the tubecavity and creates damaging arcs.The following precautions should beobserved regarding air conditioningsystems:1. Air conditioners have an ARInominal cooling capacity rating. Inselecting an air conditioner, do notassume that this number can beequated to the requirements ofthe site. Make certain that thecontractor uses the actualconditions that are to bemaintained at the site indetermining the size of the airconditioning unit. With the desiredconditioned room temperatureunder 80° F, the unit must bederated, possibly by a substantialamount.2. Do not have the air conditionerblowing directly onto thetransmitter. Condensation mayoccur on, or worse in, thetransmitter under certainconditions.3. Do not isolate the front of thetransmitter from the back with thethought of air conditioning onlythe front of the unit. Cooling air isdrawn in at the front of alltransmitters and in the front andback of others. Any attempt toisolate the front from the rear willadversely affect the flow of coolingair.4. Interlocking the transmitter withthe air conditioner isrecommended to keep thetransmitter from operating withoutthe necessary cooling.5. The periodic cleaning of all filtersis a must.When using ventilation alone, thefollowing general statements apply:1. The blower, with attendant filters,should be on the inlet, therebypressurizing the room andpreventing dirt from entering thetransmitter.2. The inlet and outlet vents shouldbe on the same side of thebuilding, preferably the leewardside. As a result, the pressuredifferential created by wind will beminimized. Only the outlet ventmay be released through the roof.3. The inlet and outlet vents shouldbe screened with 1/8-inchhardware cloth (preferred) orgalvanized hardware cloth(acceptable).4. Cooling air should enter the roomas low as practical but in no casehigher than four feet above thefloor. The inlet must be locatedwhere dirt, leaves, snow, etc., will
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures325A, Rev. 0 4-3not be carried in with the coolingair.5. The exhaust should be located ashigh as possible. Some ducting isusually required to insure thecomplete flushing of heated airwith no stagnant areas.6. The filter area must be largeenough to insure a maximum airvelocity of 300 feet per minutethrough the filter. This is not aconservative number but a never-exceed number. In a dusty orremote location, this numbershould be reduced to 150 CFM.7. The inlet and outlet(s) must haveautomatic dampers that close anytime the ventilation blower is off.8. In those cases in whichtransmitters are regularly off for aportion of each day, atemperature-differential sensorthat controls a small heater mustbe installed. This sensor willmonitor inside and outsidetemperatures simultaneously. Ifthe inside temperature falls towithin 5° F of the outsidetemperature, the heater will comeon. This will prevent condensationwhen the ventilation blower comeson and should be used even in thesummer.9. A controlled-air bypass systemmust be installed to prevent thetemperature in the room fromfalling below 40° F duringtransmitter operation.10. The blower should have twospeeds, which are thermostaticallycontrolled, and be interlocked withthe transmitter.11. The blower on high speed must becapable of moving the requiredvolume of air into a half inch ofwater pressure at the requiredelevation. The free air deliverymethod must not be used.12. Regular maintenance of the filters,if used, can not beoveremphasized.13. Tube transmitters should not relyon the internal blower to vent thecooling air at elevations above4000 feet. For external venting,the air vent on the cabinet topmust be increased to an 8-inchdiameter for a 1-kW transmitterand to a 10-inch diameter for 5-kW and 10-kW transmitters. Anequivalent rectangular duct maybe used but, in all cases, theoutlet must be increased by 50%through the outlet screen.14. It is recommended that a site planbe submitted to Axcera forcomments before installationbegins.In calculating the blower requirements,filter size, and exhaust size, if the totalload is known in watts, 2000 CFM into ½inch of water will be required for each5000 watts. If the load is known in BTUs,2000 CFM into ½ inch of water will berequired for each 17,000 BTUs. The inletfilter must be a minimum of sevensquare feet, larger for dusty and remotelocations, for each 5000 watts or 17,000BTUs. The exhaust must be at least foursquare feet at the exhaust screen foreach 5000 watts or 17,000 BTUs.The information presented in this sectionis intended to serve only as a generalguide and may need to be modified forunusually severe conditions. Acombination of air conditioning andventilation should not be difficult todesign (see Figure 4-1). Systeminterlocking and thermostat settingsshould be reviewed with Axcera.
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures325A, Rev. 0 4-4As with any equipment installation, it isalways good practice to consult themanufacturer when questions arise.Axcera can be contacted at (724) 873-8100.Figure 4-1. 1 kW Minimum Ventilation Configuration4.2 Unpacking the Cabinets andTraysNote: Air conditioning and anyrelated heat exhaust ducts should bein place before continuing with theinstallation of the transmitter.Thoroughly inspect the cabinets and allother materials upon their arrival. Axceracertifies that upon leaving our facility theequipment was undamaged and in properworking order. The shipping containersshould be inspected for obvious damagethat indicates rough handling. Check fordents and scratches or broken switches,meters, or connectors. Any claimsagainst in-transit damage should bedirected to the carrier. Inform Axcera asto the extent of any damage as soon aspossible.Remove the cabinet and the trays fromthe crates and boxes. Remove the strapsthat hold the cabinet to the shipping skidand slide the cabinet from the skid.Remove the plastic wrap and foamprotection from around the cabinet. Donot remove any labeling or tags from anycables or connectors; these areidentification markers that makeassembly of the transmitter much easier.Remove the two L-brackets, mounted onthe front panel rails, which held the traysin place during shipment. The trays aremounted in the cabinet using ChassisTrak cabinet slides as shown in Figure4-2. The tray slides are on the top andthe bottom of the VHF amplifier trays andon the sides of the VHF exciter tray.Inspect the trays for any loose hardwareor connectors, tightening as needed.
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures325A, Rev. 0 4-5Figure 4-2. Chassis Trak Cabinet SlidesOpen the rear door. Inspect the interiorof the cabinet for packing materials andcarefully remove any packing materialsthat are found. Slowly slide each tray inand out to verify that they do not rubagainst each other and have norestrictions to free movement.4.3 Installing the Cabinets and TraysIt may be necessary to adjust theposition of the trays to keep them fromrubbing. This is accomplished byloosening the cabinet slide mountingbolts that hold the front of the slide tothe mounting frame of the cabinet andmoving the tray up or down, as needed,to correct for the rubbing.The air intake to the 500-watttransmitter is only intended for room air.The cabinet should be positioned foradequate air intake and exhaust; theopening of the rear door, if present;access to the trays, including slidingthem out for testing; the main AChookup; and the installation of the outputtransmission line. The cabinet should begrounded using copper strappingmaterial and should be permanentlymounted to the floor of the site using theholes in the bottom of the cabinet.Once the cabinet is in place, and thetrays are checked for damage, the mainAC hookup can be made.Caution: Before connecting the 220VAC, make certain that all of thecircuit breakers associated with thetransmitter have been switched off.The main AC input circuit to the 500-watttransmitter should be a 40-amp, 230-VAC line, using AWG 6 wire, inside of a1-1/4-inch conduit.The 220 VAC input connections are madeto terminal block TB1, which is part ofthe AC distribution panel, near the upperright-hand, rear portion of thetransmitter: terminals 1 and 4 (220 VAC)and terminal 3 (chassis ground).The output of the (A9) bandpass filterassembly at (A5-J2), which is an “N”connector, should connect to thetransmission line for the antenna system.This completes the unpacking andinstallation of the 325A 500-watt VHFtelevision transmitter. Refer to the setupand operation procedures that followbefore applying power to the transmitter.
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures325A, Rev. 0 4-64.4 Setup and OperationInitially, the transmitter should be turnedon with the RF output at (A9-A5-J2) thecoupler assembly terminated into adummy load of at least 500 watts. If aload is not available, check that theoutput of the coupler assembly isconnected to the antenna.If the optional (A12) A/V input andremote interface assembly is not presentin the system, connect the basebandbalanced audio input to the terminalblock TB1 or the composite audio input toBNC jack J3 or J13 on the rear of the VHFexciter. The baseband audio input canremain connected when using the(Optional) 4.5-MHz composite input, ifpresent, without affecting the operationof the tray. Connect the baseband videoinput to BNC jack J2 or J1 also on therear of the VHF exciter or, if the(optional) 4.5-MHz composite input kit ispurchased, connect the 4.5-MHzcomposite input to BNC jack J2 or J1. Touse the 4.5-MHz composite input, the4.5-MHz composite input must beconnected to J2 or J1 and the basebandselect must be removed from J7-6 andJ7-7 on the rear of the tray. To use thebaseband video and audio inputs, thebaseband video input must be connectedto J2 or J1, the baseband audio must beconnected to the proper jack, and thebaseband select must be connected fromJ7-6 and J7-7.If the optional (A12) A/V input andremote interface assembly is present inthe system, the baseband balanced audioinput connects to the terminal block TB1or the composite audio input to BNC jackJ6. The baseband audio input can remainconnected when the 4.5-MHz compositeinput is in use without affecting theoperation of the tray. Connect thebaseband video input to BNC jack J2 onthe A/V input and the remote interfaceassembly or, if the (optional) 4.5-MHzcomposite input kit is purchased, connectthe 4.5-MHz composite input to BNC jackJ2. To use the 4.5-MHz composite input,the 4.5-MHz composite input must beconnected to J2 and the baseband selectmust be removed from J7-6 and J7-7 onthe rear of the VHF exciter tray. To usethe baseband video and audio inputs, thebaseband video input must be connectedto J2, the baseband audio must beconnected to the proper jack, and thebaseband select must be connected fromJ7-6 and J7-7 on the rear of the VHFexciter tray.Switch on the main AC, VHF exciter, andthe amplifier #1 and amplifier #2 circuitbreakers on the AC distribution panelfacing the rear of the cabinet andmounted behind the rear door. On theVHF exciter tray, switch theOperate/Standby switch to Standby andthe Auto/Manual switch to Manual.Normal operation of the transmitter is inAutomatic. Automatic operation uses thevideo input to the VHF exciter as anOperate/Standby switch. In Auto, if theinput video is lost for approximately 7seconds, the transmitter willautomatically revert to Standby and,when the video signal is restored, thetransmitter will quickly return to Operate.Move the Operate/Standby switch on theVHF exciter tray to Operate. Observe thepower supply reading, +48 V, on thefront panel of the VHF amplifier trays.Note: If the transmitter does notswitch to Operate when theOperate/Standby switch is placed inOperate, check that an externalinterlock plug, with a jumper wiredfrom pins 23 to 24, is connected tojack J11 on the rear of the VHFexciter. If (A12) the (optional) A/Vinput and remote interface assemblyare present in the system, theexternal interlock plug, with ajumper wired from pins 21 to 22, isconnected to jack J9 on theassembly.On the VHF exciter tray, look at the frontpanel meter reading in the % VisualPower position; it should read 100%.
500-Watt VHF Low Band Transmitter Chapter 4, Installation and Setup Procedures325A, Rev. 0 4-7If necessary, readjust the screwdriveradjust power pot on the front panel ofthe VHF exciter for 100%. As the powerlevel is being checked, observe the meterreading in the % Reflected Powerposition. If the % Reflected Power is veryhigh, above 10%, a problem exists withthe output coaxial lines and they willneed to be checked. A center bulletmissing from the coax lines or loose boltson the connections can cause thisproblem. Return the Operate/Standbyswitch to Standby.The gain and phase controls on the frontpanels of the individual VHF amplifiertrays were adjusted at the factory toobtain an output of 100% for thetransmitter and should not need to bereadjusted.The front panel readings on the individualVHF amplifier trays may not be the same.Refer to the Test Data Sheet for thetransmitter to compare the final readingsfrom the factory with the readings oneach of the trays after the setup. Theyshould be very similar. If a reading is offby a significant amount, refer to thephasing and power adjustmentprocedures for the VHF amplifier trays inChapter 5, Detailed AlignmentProcedures, of this manual before tryingto make any adjustments.If a dummy load is connected to thetransmitter, switch the unit to Standbyand switch off the main AC circuitbreaker. Remove the dummy load andmake all of the connections that areneeded to connect the transmitter to theantenna. Switch the main AC circuitbreaker on and the Operate/Standbyswitch to Operate. Adjust the outputpower screwdriver pot to achieve anoutput of 100%.If the transmitter is already connected tothe antenna, check that the output is100%. If necessary, adjust the powerscrewdriver pot.This completes the transmitter setup andoperation procedures for the 325A VHFlow band transmitter. The transmittercan now be operated normally.If a problem occurred during the setupand operation procedures, refer toChapter 5, Detailed AlignmentProcedures, of this manual for moreinformation.

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