Ramsey Electronics DA25 Stereo System User Manual
Contents
1. the load at the end of the transmission line is not the desired impedance the signal will actually reflect back down the line and precipitate a high VSWR Typical usable VSWR ratios are in the 3 0 1 0 range for commercial available communications equipment while the robust discone design actually outperforms these at many frequencies with a typical ratio of 1 5 1 0 or better A 1 0 1 0 ratio indicates the best match possible resulting in no wasted signal reflection DISCONE DESCRIPTION Getting back to the kit at hand let us apply some of the theory we just discussed Notice that the discone antenna is predominately two sections the upper disk and lower cone section To allow for the large frequency range of the antenna notice how the lower cone section of the antenna slopes away from the top disk section This design allows for a smooth transition between the multiple wavelengths that we hope to receive without any discontinuities in between This is an ideal configuration for an omni directional antenna response pattern The coaxial cable mounts directly to the provided circuit board plate which in turn will be connected to both the conic section as well as the top disk of the antenna The cable has been supplied with a crimped BNC type connector at one end for ease of connection to your receiver The discone dimensions have been calculated such that the usable performance range is between 450 MHz to 22. to cut through the center conductor You will want to trim about 1 1 2 off of the exposed braid to aid with further installation Coaxial Cable Center Insulation Center Conductor Braid 2 inches 3 inches DA25 12 1 Carefully tin the center conductor of the cable by adding a small amount of solder to the twisted center conductor Use care not to leave the soldering iron in contact with the wire for too long as it can melt the center insulation Tinning allows us easier installation of the coaxial cable to the circuit board assembly and minimizes the chance of overheating the wire when this installation occurs Have a look at the diagram to see what the complete pre assembled cable should look like 2 Inspect the circuit board assembly Notice that the top side of the as sembly is blank while the bottom side is almost completely filled with tinned copper We will use this circuit board to transition form the coaxial cable assembly to the antenna 3 Insert the full length tinned center conductor wire through the P1 hole in the center of the circuit board This wire will connect the circuit board as sembly to the disk section of the antenna and will also connect to the cen ter conductor of the coaxial cable Push until the center insulation of the cable is almost flush with the circuit board Leave enough of a gap to sol der the tinned center conductor in place from the bottom side 4 Gently s
3. 5 before we snapped the rope the sound waves would arrive much quicker than the rope wave would In the case of radio waves the rate at which the waves travel is much faster reaching the speed of light 186 000 miles second or about 3x108 meters second in a vacuum Radio waves do travel slightly slower in air however In a wire transmission line they travel even slowly Frequency and Wavelength Since all antennas collect electromagnetic waves lets take a moment to think about the wave motion of the radio wave itself Try to picture a repeating sinusoidal waveform moving down a line oscillating A wave that repeats itself has a certain period amount of time that it takes to complete a full cycle Since this cycle is regular we say that the wave has a frequency of repetition This frequency in fact is the reciprocal of the time it takes for the wave to complete one full cycle mathematically speaking f 1 T By the same token the time and frequency are related by the expression T 1 f The distance in free space that the wave takes to repeat itself is said to be the wavelength and can be calculated using the same velocity equation By rearranging the velocity equation algebraically we can say that the Distance Velocity x Time Since we will approximate the velocity to be the speed of light c once the Time is determined we can solve for the distance traveled which is the wavelength usually denoted as the Greek
4. 500 MHz with a typical VSWR of 2 0 1 0 or less DA25 9 Ramsey offers two models of this particular antenna one with no active components and the other with a low noise preamplifier to further boost the antenna gain The DA25 kit which you are about to assemble is the non preamplified version The advantages to this particular model are its ease of use no external power required and the fact that it can just as easily be used as a transmit antenna as well Experimenters have used this particular design for a host of transmit applications including increasing the distance of their PC s wireless LAN to boosting the range of cordless phones However if your particular application is for reception only and power is not an obstacle you may decide to upgrade to the preamplified version of this kit the DAP25 The good news is if you have not begun assembly you may return your kit for full credit towards the amplified version Coaxial Cable Shield Coaxial Cable Center Conductor Disk Cone Mounting Pipe Coaxial Cable DA25 10 PARTS SUPPLIED WITH YOUR DA25 KIT 1 3 Qt funnel cone 1 7 inch pie plate CAUTION EDGES MAY BE SHARP 3 6 32 x 1 4 screws 3 6 32 M F stand offs 3 6 32 nuts 1 DCA2 circuit board 1 PVC coupling 1 3 BNC cable RAMSEY Learn As You Build KIT ASSEMBLY There are solder connections on the DA25 printed circuit board Therefore PLEASE take us seriou
5. 70A Speech Scrambler BS1 Bullshooter Digital Voice Storage Unit AVS10 Automatic Sequential Video Switcher WCT20 Cable Wizard Cable Tracer ECG1 Electrocardiogram Heart Monitor LC1 Inductance Capacitance Meter RAMSEY AMATEUR RADIO KITS DDF1 Doppler Direction Finder HR Series HF All Mode Receivers QRP Series HF CW Transmitters CW7 CW Keyer CPO3 Code Practice Oscillator QRP Power Amplifiers RAMSEY MINI KITS Many other kits are available for hobby school Scouts and just plain FUN New kits are always under development Write or call for our free Ramsey catalog DA25 KIT INSTRUCTION MANUAL Ramsey Electronics publication No MDA25 Rev 1 3 First printing November 2001 COPYRIGHT 2001 by Ramsey Electronics Inc 590 Fishers Station Drive Victor New York 14564 All rights reserved No portion of this publication may be copied or duplicated without the written permission of Ramsey Electronics Inc Printed in the United States of America DA25 3 BROADBAND DISCONE ANTENNA KIT DA25 Ramsey Publication No MDA25 Price 5 00 TABLE OF CONTENTS Introduction 4 Discone Circuit description 8 Parts list 10 Assembly instructions 11 Installation and Important notes 16 Using your DA25 17 Troubleshooting guide 17 Warranty 19
6. A MOUNT When you are satisfied that your solder connections are just right we will install the PVC antenna mast coupler included with the kit The mast mounting is a 1 PVC coupler We recommend that you glue the coupling into place with some RTV or contact cement Be sure to fit the coupler firmly into place after threading the cable assembly through it If the glue sets up with the coupling in a little tilted you will forever see a slightly off balance discone IMPORTANT NOTE CONCERNING OUTDOOR USAGE Many of the metal components contained in your discone antenna will oxidize and rust if left exposed to direct weather It is recommended that if you are planning on permanently mounting the antenna outdoors you coat the entire unit with an enamel paint before installing Glue Here DA25 17 USING YOUR DA25 DISCONE ANTENNA Now we are ready for the moment of truth the running of your discone an tenna Were pretty sure by now you have a place selected to install it you can use a couple of nylon wire ties and a bit of 1 PVC pipe to fasten it into place A fairly good poor mans test is to search on your scanner or radio receiver for a weak station one that is barely breaking the threshold of your receivers sensitivity Note your signal strength indication of the station and proceed to disconnect your existing antenna and replace it with your DA25 If your like our many satisfied customers your notice a significant imp
7. DA25 1 BROADBAND DISCONE ANTENNA KIT Ramsey Electronics Model No DA25 Looking for a broadband antenna with a full 360 degree coverage Discover what communication professionals have known for years using a discone antenna Use this antenna to bring a multitude of signals out of the noise making it ideal for scanners and Ultra High through Microwave Frequency receivers Search the airwaves for signals with this unique kit Omni directional performance no need to point in any direction Learn about antenna theory and what makes the discone an ideal broadband antenna Covers all frequencies between 450 MHz and 2500 MHz and you ll learn why E Z cable connection industry standard BNC type connector Outperforms models costing tens to hundreds of dollars more Super small in size for easy mounting almost anywhere An ideal apartment size antenna All hardware and pre drilled metal work included Forgiving design gives you a high performance antenna each and every time DA25 2 RAMSEY TRANSMITTER KITS FM100B Professional FM Stereo Transmitter FM25B Synthesized Stereo FM Transmitter MR6 Model Rocket Tracking Transmitter TV6 Television Transmitter RAMSEY RECEIVER KITS FR1 FM Broadcast Receiver AR1 Aircraft Band Receiver SR1 Short wave Receiver SC1 Short wave Converter RAMSEY HOBBY KITS SG7 Personal Speed Radar SS
8. KIT ASSEMBLY AND INSTRUCTION MANUAL FOR RAMSEY ELECTRONICS INC 590 Fishers Station Drive Victor New York 14564 Phone 585 924 4560 Fax 585 924 4555 www ramseykits com DA25 4 INTRODUCTION In today s ever growing wireless society it almost seems a bit ironic that antennas have become less and less the topic of interest in hobbyist circles The recent advances in wireless technology have shrunk antennas to ever smaller an unobtrusive sizes An example of this is the cable television industry They have removed the larger traditional antenna arrays that were once commonplace for TV reception and replaced them with a single wire or two entering the household Advances in the semiconductor industry have provided engineers with the tools to pull the smallest signals from the airwaves with better noise performance than could have been dreamed of when the technology of radio reception was envisioned Advances in satellite technology have reduced the size of a reception dish from over 12 feet in diameter to a 1 foot round platform Antenna design certainly has not made the quantum leap that was brought on with the advances in the semiconductor industry but it is just as important as it was in those early days of radio The original aerials or reception antennas had to provide enough signal to overcome the ever present noise and allow the early receivers to detect and demodulate signals These early antennas wer
9. case by case basis The repair is 50 00 per hour regardless of the cost of the kit Please understand that our technicians are not volunteers and that set up testing diagnosis repair and repacking and paperwork can take nearly an hour of paid employee time on even a simple kit Of course if we find that a part was defective in manufacture there will be no charge to repair your kit But please realize that our technicians know the difference between a defective part and parts burned out or damaged through improper use or assembly 4 REFUNDS You are given ten 10 days to examine our products If you are not satisfied you may return your unassembled kit with all the parts and instructions and proof of purchase to the factory for a full refund The return package should be packed securely Insurance is recommended Please do not cause needless delays read all information carefully DA25 20 Price 5 00 Ramsey Publication No MDA25 Assembly and Instruction manual for RAMSEY MODEL NO DA25 RAMSEY ELECTRONICS INC 590 Fishers Station Drive Victor New York 14564 Phone 585 924 4560 Fax 585 924 4555 www ramseyelectronics com REQUIRED TOOLS Soldering Iron Ramsey WLC 100 Thin Rosin Core Solder Ramsey RTS12 Needle Nose Pliers Ramsey RTS05 Small Diagonal Cutters Ramsey RTS04 Technician Tool Set Ramsey TK405 ADDITIONAL SUGGESTED ITEMS Optivisor Magnifier Headband Ramsey OPMAG Holder for PC Boa
10. e quite large we ll talk a little more about this later due to the lower frequencies being transmitted Again more recent improvements have allowed us to use higher frequencies with significantly smaller antennas With less and less demand for consumer antennas the market price of these commodities has increased As many of us have discovered even the lowest cost antennas run in excess of one hundred dollars While they are necessary if we intend to use the antenna commercially or for television reception it simply is too much for a hobbyist to invest for use with a monitoring receiver Enter the Ramsey line of discone antennas allowing us to tinker with the airwaves at an affordable price Ramsey Antennas 101 Before we break open our discone kit lets talk about what makes an antenna tick and some of the terms used to define antenna performance How Fast are Radio Waves If one were to whip the end of a taught length of rope you could observe the wave created traveling down the rope to it s end Going back to our physics class recall that the speed of any object is the distance it travels divided by the time it takes to get there or Velocity Distance Time The time a wave takes to travel is dependant on the type of wave and the transmission medium The wave in our rope example can take seconds to traverse down the length of the medium Sound waves travel about 1100 feet every second if we called out DA25
11. er completely around the board Careful now the entire assembly will be quite hot while you are constructing this You may want to use gloves to protect your fingers from being burned Ouch Solder all the connections using enough heat to flow the ground connection completely This may take a little while depending on the wattage of your soldering pencil Whew Well we are over the worst of it now just a few more steps to complete assembly of the discone antenna Be sure to allow enough time for the assem bly to cool before proceeding any further 7 Install the disk section of the antenna flanged outer edge if present fac ing downward toward the cone assembly by passing the three 6 32 screws through the disk section of the antenna while at the same time pass ing the center conductor wire through the center hole of the disk With the 6 32 nuts provided secure the disk section of your antenna into place Solder Points DA25 15 8 Solder the center conductor wire into place on the disk section of the an tenna Trim off any excess lead that is protruding from the disk Have a look at the above diagram to help out if necessary CONGRATULATIONS Your discone antenna is now complete Have a final look over your work paying particular attention to the solder connections Remember that any problems you find now can save time and effort after the unit has been mounted Solder Here DA25 16 INSTALLATION OF THE ANTENN
12. he Resonant Frequency of the Antenna Let s explore another factor in antenna as well as radio design the resonant frequency of the circuit Recalling that we would like our discone antenna to work over a large range of frequencies we need the antenna system to be optimized for the full desired range Resonance in an antenna circuit occurs when the antenna length exactly matches the wavelength of the desired frequency To make an antenna resonant over a range of frequencies it needs to look like a multitude of lengths Looking at the desired waveform the shortest length of wire that will resonate at a given frequency is one which is just long enough to permit an electric charge to travel from one end to the other and then back again in the time of DA25 7 one radio frequency or RF cycle Since the charge traverses the wire twice the length of wire needed to permit the charge to travel the total distance in one cycle is 2 or one half the wavelength Therefore the shortest resonant wire length will be one half wavelength long Let s consider a half wavelength example to help it make sense Picture a trough with barriers at each end If a rubber ball is rolled along the trough from one end to the other it will hit the end and bounce back When it bounces back it will hit the near barrier and bounce again This will continue until the ball runs out of energy and stops If however whenever the ball returns to the near barr
13. ier it is given a push just as it starts away its back and forth motion can be kept up indefinitely as long as the impulses are timed properly In other words the rate or frequency of the impulses must be adjusted to the length of travel and the rate of travel If the timing of the impulses the push and the speed of the ball are fixed the length of the trough must be adjusted to fit In the case of the antenna the speed is constant This leaves the alternatives of adjusting the frequency or the length of wire to match a given frequency Antenna Gain Another performance specification common with antennas is their gain usually given in dBi units To understand this concept let s explore the i in the dBi unit as an isotropic source Imagine a point in space as a source of a radiating signal The signal would then expand spherically from the point source If we then move a given distance from the point source the power would be distributed uniformly in all directions The power density is uniform about an isotropic source and thus is related to the surface area of a sphere area 4x x radius 2 Although this is not practically possible it is the basis for an antenna gain specification The gain of an antenna is usually referenced in comparison to this type of source in a decibel unit with a logarithmic relationship Without getting hung up too much on logarithmic theory suffice it to say that an increase of 3 dB is equal to
14. is common problem Make sure that you have checked all the assembly steps boxes you may have forgotten one or two of them Please understand that it is nearly impossible to troubleshoot by phone any specific questions should be documented and sent to us by mail DA25 18 CONCLUSION We sincerely hope that you enjoy the use of this Ramsey product As always we have tried to compose our manual in the easiest most user friendly format that is possible As our customers we value your opinions comments and additions that you would like to see in future publications Please submit comments or ideas to Ramsey Electronics Inc Attn Hobby Kit Department 590 Fishers Station Drive Victor NY 14564 Please also feel free to visit our Website at www ramseyelectronics com and offer your observations to other kit enthusiasts as well And once again thanks from the folks at Ramsey DA25 19 The Ramsey Kit Warranty Please read carefully BEFORE calling or writing in about your kit Most problems can be solved without contacting the factory Notice that this is not a fine print warranty We want you to understand your rights and ours too All Ramsey kits will work if assembled properly The very fact that your kit includes this new manual is your assurance that a team of knowledgeable people have field tested several copies of this kit straight from the Ramsey Inventory If you need help please read through your manual caref
15. istors and received five extra 1K resistors you can pretty much be assured that the 1K ohm resistors are actually the missing 10 K parts Hum m m I guess the red band really does look orange Ramsey Electronics project kits are packed with pride in the USA If you believe we packed an incorrect part or omitted a part clearly indicated in your assembly manual as supplied with the basic kit by Ramsey please write or call us with information on the part you need and proof of kit purchase 3 FACTORY REPAIR OF ASSEMBLED KITS To qualify for Ramsey Electronics factory repair kits MUST 1 NOT be assembled with acid core solder or flux 2 NOT be modified in any manner 3 BE returned in fully assembled form not partially assembled 4 BE accompanied by the proper repair fee No repair will be undertaken until we have received the MINIMUM repair fee 1 2 hour labor of 25 00 or authorization to charge it to your credit card account 5 INCLUDE a description of the problem and legible return address DO NOT send a separate letter include all correspondence with the unit Please do not include your own hardware such as non Ramsey cabinets knobs cables external battery packs and the like Ramsey Electronics Inc reserves the right to refuse repair on ANY item in which we find excessive problems or damage due to construction methods To assist customers in such situations Ramsey Electronics Inc reserves the right to solve their needs on a
16. letter lambda reducing our equation to v x T In English the wavelength is equal to the velocity multiplied by the period of the waveform Pretty neat huh One Wavelength One Cycle Some Amount of Time Electromagnetic Wave DA25 6 What Are We Driving At Time to pull some of that theory together and get some answers Since v x T And T 1 f We can substitute and get v f Since the velocity equals c we wind up with c f The wavelength of the radio wave equals the speed of light divided by the frequency Lets plug some numbers into our equation and work out a few wavelengths We should notice some other properties of electromagnetic waves If f 450 MHz the wave cycles 450 million times in a second then 3x 108 450 x 106 or 666 meters for a full wavelength If f 2500 MHz the wave cycles 2500 million times in a second then 3x 108 2500 x 106 or 120 meters for a full wavelength It s important to note that as the frequency of a wave increases its wavelength decreases Keeping in mind the introduction section where we talked about antenna size lets consider the old days of radio The common use of low frequencies meant much longer wavelengths and significantly larger antennas for reception Today s modern electronic devices tend to operate at much higher frequencies and thereby require smaller antennas to operate properly Determining t
17. pread the trimmed braid to the area immediately around the P1 hole Be sure that the braid ONLY contacts the tinned copper ground plane area around P1 Trim off any stray wires that may short circuit to the adjacent mounting rings or the center conductor solder pad DA25 13 Now we are getting somewhere All your careful preparation will pay dividends as we install the coax cable to the circuit board We did this first as it can be quite difficult to perform this operation once the circuit board is installed on to the cone 5 Using the 3 6 32 screws provided insert them through the circuit board as sembly as shown Fasten the screws into place using the 6 32 stand offs pro vided Be careful not to over tighten the nylon parts or they may shear off Now we are getting to probably the most difficult solder connection of the entire antenna kit We will solder the circuit board assembly to the funnel cone This may take considerably more heat than a single 25 watt iron can provide you may wish to use two irons or an additional heat source to speed things up Bottom Copper Plated side Coaxial Cable Solder Here Solder Here Bottom Copper Plated side Coaxial Cable DA25 14 6 Install the circuit board assembly to the funnel cone as shown Use care to center the circuit board before you solder the assembly completely It may be easier if you tack solder the board into place before you run a ring of sold
18. rd Parts Ramsey RTS13 Desoldering Braid Ramsey RTS08 DA25 DISCONE ANTENNA KIT Quick Reference Page Guide Introduction 4 Discone Circuit description 8 Parts list 10 Assembly instructions 11 Installation and Important notes 16 Using your DA25 17 Troubleshooting guide 17 Warranty 19 TOTAL SOLDER POINTS 4 ESTIMATED ASSEMBLY TIME Beginner 2 hrs Intermediate 1 25 hrs Advanced 0 75 hrs
19. rovement in signal quality Try this test on several frequencies throughout the band and find out just how poorly your original antenna was working TROUBLESHOOTING GUIDE If your DA25 does not work at all re check the following Correct connection of the soldered coaxial cable ends Sometimes the ac tion of installing the PVC pipe stresses the wire and can cause a break Is that disk on the top soldered to the feed through wire Make sure that the wire hasn t folded under the disk and shorted by touching the ground connections somewhere all solder connections Still having trouble While we had hoped that it wouldn t come to this if you are still having trouble with your DA25 here are a few additional suggestions Use a methodical logical troubleshooting technique Most problems can be solved using common sense A volt ohm meter and a clear head are usually all that are needed to correct any problem Most problems are due to misplaced parts and or bad solder connections Working backwards through the assembly steps will often lead you to the problem Re visit the extensive theory of operation include in this manual and try to apply to your specific problem Have another set of eyes look through your work Here at the shop we have often run into a stone wall of a problem only to have a fellow technician see our obvious error It is sometimes very difficult to see your own mistake taking a break can often solve th
20. sly when we say that good soldering is essential to the proper operation of your discone antenna kit Use a 25 watt soldering pencil with a clean sharp tip Use only rosin core solder intended for electronics use Use bright lighting a magnifying lamp or bench style magnifier may be helpful We have a two fold strategy for the order of the following kit assembly steps First we install parts in physical relationship to each other so there s minimal chance of inserting wires into wrong holes Second whenever possible we install in an order that fits our Learn As You Build Kit building philosophy This entails describing the circuit that you are building instead of just blindly installing components We hope that this will not only make assembly of our kits easier but help you to understand the circuit you re constructing For each part our word Install always means these steps 1 Pick the correct component with the proper value to start with 2 Insert it into the correct PC board location 3 Orient it correctly following the PC board drawing and the written directions for all parts especially when there s a right way and a wrong way to solder it in 4 Solder all connections unless directed otherwise Use enough heat and solder flow for clean shiny completed connections 5 Trim or nip the excess component lead wire after soldering DA25 11 DA25 DISCONE ANTENNA KIT ASSEMBLY Although we know that you are an
21. twice the power being present An increase of 10 dB is equivalent to a gain factor of 10 For example a 1 Watt signal with a gain of 3 dB equals two Watts while the same power with 10 dB gain is 10 Watts Although we are using our discone as a receiving antenna the rules of antenna gain are reciprocal so we can count on at least a 3 dBi improvement in the signal power over the entire frequency range DA25 8 What About Impedance Matching and VSWR Another consideration with electromagnetic wave antennas is the match presented to either the receiver or transmitter In our discussion of wavelength and resonant frequencies it became apparent that the length of the antenna is critical to match that of the desired frequency A small error in length can detune an antenna significantly and inhibit the antennas performance For many communications systems 50 or 75 Ohms are the desired magical impedance values desired for the antenna systems The proper impedance allows for maximum power to transfer to or from the antenna system with a minimum of loss Even with the high frequencies being used we want the antenna to appear as a proper load In this way the antenna presents a good match to the receiver Luckily for us the discone antenna exhibits exceptional performance in the impedance matching department The Voltage Standing Wave Ratio VSWR of an antenna system is another measure of this impedance match At RF frequencies if
22. ully All information required to properly build and test your kit is contained within the pages 1 DEFECTIVE PARTS It s always easy to blame a part for a problem in your kit Before you conclude that a part may be bad thoroughly check your work Today s semiconductors and passive components have reached incredibly high reliability levels and it s sad to say that our human construction skills have not But on rare occasions a sour component can slip through All our kit parts carry the Ramsey Electronics Warranty that they are free from defects for a full ninety 90 days from the date of purchase Defective parts will be replaced promptly at our expense If you suspect any part to be defective please mail it to our factory for testing and replacement Please send only the defective part s not the entire kit The part s MUST be returned to us in suitable condition for testing Please be aware that testing can usually determine if the part was truly defective or damaged by assembly or usage Don t be afraid of telling us that you blew it we re all human and in most cases replacement parts are very reasonably priced 2 MISSING PARTS Before assuming a part value is incorrect check the parts listing carefully to see if it is a critical value such as a specific coil or IC or whether a RANGE of values is suitable such as 100 to 500 uF Often times common sense will solve a mysterious missing part problem If you re missing five 10K ohm res
23. xious to complete the assembly of your an tenna kit it is necessary to assemble it in a specific order to insure the proper operation of the finished unit Try to avoid the urge to jump ahead installing components Since you may appreciate some warm up soldering practice as well as a chance to put some landmarks on the PC board we ll first install some of the larger mounting components This will also help us to get acquainted with the up down left right orientation of the circuit board can you do that with a circu lar board Look carefully at the component layout diagrams in the manual to help with your assembly Use the boxes to check off your progress Check all received parts against the parts list The parts list describes the vari ous markings that may be found on the kit parts Carefully sort the parts into small piles an empty egg tray does nicely for this purpose to aid in finding the correct part at the required time Enough of that lets get started First we will prepare the coaxial cable for its installation to the circuit board We need to break out the two wire components of the cable Trim about 3 of the outer insulation from the cable being careful not to cut through the outer braid of wire Using a fine pointed tool carefully un braid about 2 1 4 of the outer conductor and fan out the loose strands of wire Once this is accomplished trim back about 2 of the center insulation Be careful not
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