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blocking radio waves
When I build my new shack, I was thinking about lining the inside of the
plywood with something, before it is installed, that would block outside radio transmissions inside the shack. Mostly in the 2 meter range and higher. Would simple aluminum foil work? If so what frequency range could I expect it to work in? If not any suggestions on material? The cheaper the better. I know there is a term for a room like this but I can not rember it..faraday chamber? The shack will be 12 foot by 16 foot, right next to my 60' tower, with HF and 2m antennas on it. I have no idea how they will interact with such a building... Thanks Joe |
blocking radio waves
On Tue, 19 Jun 2007 18:50:59 -0400, "merlin-7"
wrote: Would simple aluminum foil work? Hi Joe, Sure, but bonding one sheet to the next overlapping one might "foil" your goal. Few of us with dominant Y genes realize that aluminum foil is wax (an insulator) coated on one side. If so what frequency range could I expect it to work in? Most. Depends on the gaps. Staple it every inch, and it may work from LF to VHF. I know there is a term for a room like this but I can not rember it..faraday chamber? Farady shield, room, chamber.... The shack will be 12 foot by 16 foot, right next to my 60' tower, with HF and 2m antennas on it. I have no idea how they will interact with such a building... Are you doing the windows and doors too? Most doors have a gasket of fringed fingers making contact with the conductive door. You need to choke EVERY wire penetrating the walls. Any exception and your room will fill like an RF gong. 73's Richard Clark, KB7QHC |
blocking radio waves
Try "Bronze, or copper" screen- this is used in
"Radio Shops", to limit RF interference to services being used, so as to test (proof of performance) equipment , without causing interference to each other ! A.K.A. "Faraday Shield" - Jim NN7K merlin-7 wrote: When I build my new shack, I was thinking about lining the inside of the plywood with something, before it is installed, that would block outside radio transmissions inside the shack. Mostly in the 2 meter range and higher. Would simple aluminum foil work? If so what frequency range could I expect it to work in? If not any suggestions on material? The cheaper the better. I know there is a term for a room like this but I can not rember it..faraday chamber? The shack will be 12 foot by 16 foot, right next to my 60' tower, with HF and 2m antennas on it. I have no idea how they will interact with such a building... Thanks Joe |
blocking radio waves
On Tue, 19 Jun 2007 21:47:42 -0400, "merlin-7"
wrote: I can deal with that even if I have to disconnect everything when needed. I just need a RF quiet room from time to time for searching for birdies and the like. Hi Joe, This is far easier to obtain through good grounding practices (as I've discussed in the past hour in another thread). 73's Richard Clark, KB7QHC |
blocking radio waves
"Richard Clark" wrote in message ... On Tue, 19 Jun 2007 18:50:59 -0400, "merlin-7" wrote: Would simple aluminum foil work? Hi Joe, Sure, but bonding one sheet to the next overlapping one might "foil" your goal. Few of us with dominant Y genes realize that aluminum foil is wax (an insulator) coated on one side. I understand this and was thinking about overlap and staples or possibley tacks. I guess I also have the Y gene, the only reason I was thinking about foil is that it is cheap and easy to work with. Wire screen would work also (I think) but much simpler, glueing foil to plywood than screen. If so what frequency range could I expect it to work in? Most. Depends on the gaps. Staple it every inch, and it may work from LF to VHF. I know there is a term for a room like this but I can not rember it..faraday chamber? Farady shield, room, chamber.... The shack will be 12 foot by 16 foot, right next to my 60' tower, with HF and 2m antennas on it. I have no idea how they will interact with such a building... Are you doing the windows and doors too? Most doors have a gasket of fringed fingers making contact with the conductive door. No window, kinda bytes but needed. You did get me on the door, I didnt think of that one (DUH) I guess I will have to use a metal door or coat it with foil and strap it to the rest of the foil. You need to choke EVERY wire penetrating the walls. Any exception and your room will fill like an RF gong. This is going to be a whole new problem. With solar panel wire runs, coax runs for radio gear etc. I can deal with that even if I have to disconnect everything when needed. I just need a RF quiet room from time to time for searching for birdies and the like. I may even section off a small area of the shack for that.( big enough for a frequincy counter, a few other test instraments and the gear being tested. Thanks joe KI4ILB 73's Richard Clark, KB7QHC |
blocking radio waves
"merlin-7" wrote in message ... When I build my new shack, I was thinking about lining the inside of the plywood with something, before it is installed, that would block outside radio transmissions inside the shack. Mostly in the 2 meter range and higher. Would simple aluminum foil work? If so what frequency range could I expect it to work in? If not any suggestions on material? The cheaper the better. I know there is a term for a room like this but I can not rember it..faraday chamber? The shack will be 12 foot by 16 foot, right next to my 60' tower, with HF and 2m antennas on it. I have no idea how they will interact with such a building... Thanks Joe Joe, When working with a Faraday cage, remember that safety is of the utmost importance. Any mains voltage electrical supply fed into the cage must come in via an isolating transformer so that the mains voltages are floating. This will reduce the risk of electric shock if a chassis becomes live with respect to the earthed cage. It should not be possible to reach any 'ordinary' mains powered sockets, switches or devices outside the cage area when you are within the cage. No external mains earth should be brought into the cage area. The Faraday cage should be provided with its own completely separate electrical earth. Mains sockets within the cage area should not contain an earth connection. British Standard 7671 contains some basic details but other equivalent legislation applies in many countries. It's not just about slapping up some tin foil around the walls, floors and ceiling and then strapping it to the nearest convenient earth point. Your safety and that of others who may enter the area are paramount. Mike G0ULI |
blocking radio waves
merlin-7 wrote:
Richard Clark wrote: merlin-7" wrote: Would simple aluminum foil work? Hi Joe, Sure, but bonding one sheet to the next overlapping one might "foil" your goal. Few of us with dominant Y genes realize that aluminum foil is wax (an insulator) coated on one side. I understand it's typically a very thin plastic or paper, to which the aluminum is laminated (http://en.wikipedia.org/wiki/Aluminium_foil). Alternatively, aluminum window screen will work just as well, unless you're working with frequencies approaching 19 GHz. This assumes screening of 1/16"x1/16" opening, and allowing for no more than 1/10 wavelength. I understand this and was thinking about overlap and staples or possibley tacks. If (before you put the wall panels up) you attach a conductive strip of foil or screen to the edges of the wall studs, you will have your overlap. If you then use screws instead of nails, you can then (relatively) easily gain access for future wiring changes. I guess I also have the Y gene, the only reason I was thinking about foil is that it is cheap and easy to work with. Wire screen would work also (I think) but much simpler, glueing foil to plywood than screen. If so what frequency range could I expect it to work in? Most. Depends on the gaps. Staple it every inch, and it may work from LF to VHF. I know there is a term for a room like this but I can not rember it..faraday chamber? Farady shield, room, chamber.... The shack will be 12 foot by 16 foot, right next to my 60' tower, with HF and 2m antennas on it. I have no idea how they will interact with such a building... Are you doing the windows and doors too? Most doors have a gasket of fringed fingers making contact with the conductive door. No window, kinda bytes but needed. Welded "chicken wire" with ¼x¼" openings over any windows will pass light but will represent less than 1/10 wavelength up to 4725 MHz. You did get me on the door, I didnt think of that one (DUH) I guess I will have to use a metal door or coat it with foil and strap it to the rest of the foil. Chomerics (http://www.chomerics.com/) and Tech Etch (http://www.tech-etch.com/) -- among others -- produce compressible shielding material that can be used to make a door RF-tight. You need to choke EVERY wire penetrating the walls. Any exception and your room will fill like an RF gong. This is going to be a whole new problem. With solar panel wire runs, coax runs for radio gear etc. I can deal with that even if I have to disconnect everything when needed. I just need a RF quiet room from time to time for searching for birdies and the like. I may even section off a small area of the shack for that.( big enough for a frequincy counter, a few other test instraments and the gear being tested. In that case, think about using a suitably-sized cardboard box (coated with conductive material). It has the potential of being folded up when not in use! Thanks joe KI4ILB 73's Richard Clark, KB7QHC |
blocking radio waves
Sure, but bonding one sheet to the next overlapping one might "foil" your goal. Few of us with dominant Y genes realize that aluminum foil is wax (an insulator) coated on one side. I understand it's typically a very thin plastic or paper, to which the aluminum is laminated It is just plain aluminium, no wax, no paper, no plastic. Just think of the results if you cooked something wrapped in a foil with a wax or plastic coating!!! The matt finish on one side is just a result of the way that the foil is rolled when being manufactured. Jeff |
blocking radio waves
" When working with a Faraday cage, remember that safety is of the utmost importance. Any mains voltage electrical supply fed into the cage must come in via an isolating transformer so that the mains voltages are floating. This will reduce the risk of electric shock if a chassis becomes live with respect to the earthed cage. It should not be possible to reach any 'ordinary' mains powered sockets, switches or devices outside the cage area when you are within the cage. No external mains earth should be brought into the cage area. The Faraday cage should be provided with its own completely separate electrical earth. Mains sockets within the cage area should not contain an earth connection. That is certainly not the way any screened room I have worked is has been wired, and sounds extremely dangerous. Not having the earths connected inside the room is potentially lethal should a case go live.This is a particular problem with a lot of test equipment where the input filtering causes the case to float to 1/2 mains voltage without an earth. An RCD will not protect you in this situation because of the isolating transformer. Imaging the situation where you are conducting emc tests with the UUT on an earthed copper sheet but all the test equipment is floating at 120V!! It is also a common requirement to have test equipment outside the screened room but connected to equipment inside, isolating transformers and the lack of mains earth would complicate this set up immensely. All the installations that I have seen have not used isolating transformers, just filtering on the incoming mains with a mains earth connection. Protection being provided by an RCD on the mains input. Jeff |
blocking radio waves
"Jeff" wrote in message . com... " When working with a Faraday cage, remember that safety is of the utmost importance. Any mains voltage electrical supply fed into the cage must come in via an isolating transformer so that the mains voltages are floating. This will reduce the risk of electric shock if a chassis becomes live with respect to the earthed cage. It should not be possible to reach any 'ordinary' mains powered sockets, switches or devices outside the cage area when you are within the cage. No external mains earth should be brought into the cage area. The Faraday cage should be provided with its own completely separate electrical earth. Mains sockets within the cage area should not contain an earth connection. That is certainly not the way any screened room I have worked is has been wired, and sounds extremely dangerous. Not having the earths connected inside the room is potentially lethal should a case go live.This is a particular problem with a lot of test equipment where the input filtering causes the case to float to 1/2 mains voltage without an earth. An RCD will not protect you in this situation because of the isolating transformer. Imaging the situation where you are conducting emc tests with the UUT on an earthed copper sheet but all the test equipment is floating at 120V!! It is also a common requirement to have test equipment outside the screened room but connected to equipment inside, isolating transformers and the lack of mains earth would complicate this set up immensely. All the installations that I have seen have not used isolating transformers, just filtering on the incoming mains with a mains earth connection. Protection being provided by an RCD on the mains input. Jeff Jeff If you are working surrounded on all sides by earth potential and you touch a mains live wire, then the current has a path through you to earth. In theory, only the phase (or live) wire represents a serious hazard but in the event of a chassis going live, this could be fatal. By having mains voltages floating, earthing either side of the isolated mains accidently to earth should not result in a lethal shock as the potential on the touched wire only will move down to earth. An RCD is not needed because although one side of the mains has become earthed through you, there should be no return path unless you are touching the other mains wire somehow, in which case you would get a shock whether you were in contact with earth or not! 110v Isolating transformers with their central point earthed are used on all building sites in the UK to limit shock voltages to 55v AC. In this case the transformer is earthed because it is impossible to work away from other natural earth points, girders, trusses, rods, etc. To a large extent this also prevents the risk of inappropriate equipment designed only for domestic purposes being used on site. For a Faraday cage installation, the mains supply should be completely isolated and floating using a double insulated approved transformer, no autotransformers. I previously worked in a test environment where isolating transformers and a rubber mat were regarded as adequate protection against shock. Times change. A proper Faraday cage setup does represent quite a complex environment to design, is potentially (sorry) very dangererous to work in and so it is worth looking at the official documents available for their recommendations. In the UK at least, the standards are recommendations rather than statutory requirements although you will have a tough time in court if someone is injured or killed as a result of non-compliance. Before attempting to set up this sort of testing room, consider carefully what your requirements are, the safety implications and design accordingly. Sticking a load of earthed foil and mesh around the inside of a shed is only the start. Better safe than crispy fried critter. Mike G0ULI |
blocking radio waves
If you are working surrounded on all sides by earth potential and you touch a mains live wire, then the current has a path through you to earth. In theory, only the phase (or live) wire represents a serious hazard but in the event of a chassis going live, this could be fatal. This is exactly the recommended situation in a 'normal' UK mains enviroment where all exposed metal must be bonded to mains earth (equi-potential bonding). An RCD is used to provide protection. By having mains voltages floating, earthing either side of the isolated mains accidently to earth should not result in a lethal shock as the potential on the touched wire only will move down to earth. An RCD is not needed because although one side of the mains has become earthed through you, there should be no return path unless you are touching the other mains wire somehow, in which case you would get a shock whether you were in contact with earth or not! Whilst that is true, not having a earth on equipment *inside* the screened room is still a hazard.For Example; If due to a fault a case goes to mains potential, the the case of adjacent equipment will be at some other potential, that could be anything from 'real' ground (the earthed wall potential of the cage) to perhaps 1/2 rail due the filtering components. Either way there exists the possiblity of lethal shocks. It is not easy to control what the case potential or connection will be. Commonly there will be a connection to the screened room ground on at least some of the equipment, and that will aslo be external mains ground by default. A lot of equipment cases will float to 1/2 mains due to the input filtering. Once a fault develops it is very easy for the isolation barrier provided by the transformer to be by-passed leaving you with no protection. A neutral to ground fault could go undetected forever until someone touches something at line potential. At least with an earth and an rcd there is some protection in this situation. 110v Isolating transformers with their central point earthed are used on all building sites in the UK to limit shock voltages to 55v AC. In this case the transformer is earthed because it is impossible to work away from other natural earth points, girders, trusses, rods, etc. To a large extent this also prevents the risk of inappropriate equipment designed only for domestic purposes being used on site. True, 55V is considered 'safe', but it is not common to have 110V test equipment and mains in a screened room in the UK, so it is not really relavent. For a Faraday cage installation, the mains supply should be completely isolated and floating using a double insulated approved transformer, no autotransformers. As I said this has never been the case in the dozen or so screened rooms that I have worked in!! 73 Jeff |
blocking radio waves
On 19 Jun, 23:50, "merlin-7" wrote:
When I build my new shack, I was thinking about lining the inside of the plywood with something, before it is installed, that would block outside radio transmissions inside the shack. Mostly in the 2 meter range and higher. Would simple aluminum foil work? If so what frequency range could I expect it to work in? If not any suggestions on material? The cheaper the better. I know there is a term for a room like this but I can not rember it..faraday chamber? The shack will be 12 foot by 16 foot, right next to my 60' tower, with HF and 2m antennas on it. I have no idea how they will interact with such a building... Thanks Joe We had very expensive screened rooms at Racal's Bracknell site when I worked there a few years ago. They were double-screened with copper sheet on the inside and outside. We had to use double-screened cables for some measurements, there was too much leakage from standard coax. Leon |
blocking radio waves
On Wed, 20 Jun 2007 09:26:17 -0700, Leon
wrote: We had to use double-screened cables for some measurements, there was too much leakage from standard coax. The term for this is Tri-axial cable. Often each end of the braid is left open but each connector has one braid. In other words, there is no braid to braid connection, and there is no shell to shell connection. The braids overlap. It is very simple to violate shielding through the wrong sequence of groundings from the source to the load. The art of shielding is actually found in the practice of finding your reference (ground). 73's Richard Clark, KB7QHC |
blocking radio waves
merlin-7 wrote:
... In the end, I would make sure that large of cube of metal sheet (capacitor plate) was grounded, finally, to some ground close to the shack--I'd image if that "capacitor plate" was allowed to float it may well be able to store a lethal charge in itself (if well insulated enough.) The main ground, tied to close earth ground at the shack, would be my goal, whether it filled code requirements or not ... damn inspector can't sleep in my shack! Of course, you are talking to guy who has worn a grounding strap on his wrist ... Regards, JS |
blocking radio waves
"Jeff" wrote in message . com... If you are working surrounded on all sides by earth potential and you touch a mains live wire, then the current has a path through you to earth. In theory, only the phase (or live) wire represents a serious hazard but in the event of a chassis going live, this could be fatal. This is exactly the recommended situation in a 'normal' UK mains enviroment where all exposed metal must be bonded to mains earth (equi-potential bonding). An RCD is used to provide protection. By having mains voltages floating, earthing either side of the isolated mains accidently to earth should not result in a lethal shock as the potential on the touched wire only will move down to earth. An RCD is not needed because although one side of the mains has become earthed through you, there should be no return path unless you are touching the other mains wire somehow, in which case you would get a shock whether you were in contact with earth or not! Whilst that is true, not having a earth on equipment *inside* the screened room is still a hazard.For Example; If due to a fault a case goes to mains potential, the the case of adjacent equipment will be at some other potential, that could be anything from 'real' ground (the earthed wall potential of the cage) to perhaps 1/2 rail due the filtering components. Either way there exists the possiblity of lethal shocks. It is not easy to control what the case potential or connection will be. Commonly there will be a connection to the screened room ground on at least some of the equipment, and that will aslo be external mains ground by default. A lot of equipment cases will float to 1/2 mains due to the input filtering. Once a fault develops it is very easy for the isolation barrier provided by the transformer to be by-passed leaving you with no protection. A neutral to ground fault could go undetected forever until someone touches something at line potential. At least with an earth and an rcd there is some protection in this situation. 110v Isolating transformers with their central point earthed are used on all building sites in the UK to limit shock voltages to 55v AC. In this case the transformer is earthed because it is impossible to work away from other natural earth points, girders, trusses, rods, etc. To a large extent this also prevents the risk of inappropriate equipment designed only for domestic purposes being used on site. True, 55V is considered 'safe', but it is not common to have 110V test equipment and mains in a screened room in the UK, so it is not really relavent. For a Faraday cage installation, the mains supply should be completely isolated and floating using a double insulated approved transformer, no autotransformers. As I said this has never been the case in the dozen or so screened rooms that I have worked in!! 73 Jeff Jeff You are quite correct in what you say, however working in a Faraday cage is inherently unsafe. You are surrounded on all sides by earth potential and in the event of any fault, the path is more than likely going to go through you to earth. Not a desirable situation. If mains supplies are floating, then there should be no return path to provide a lethal shock. Further provisions in the BS 7671 regs suggest that items of equipment are separated so that a person cannot be in contact with two items of equipment for precisely the reasons you give, to eliminate the risk of shock if two items of equipment are faulty with the case of each item being connected to a different side or phase of the mains. The Faraday cage is designed to prevent all external influences from affecting experiments and tests inside the cage. Careful design and consideration of the inherent risks need to be taken into account at every stage. A lot of stuff in commercial labs is hidden behind panels or incorporated into the building design at the planning stage, so may not be apparent in everyday use. Commercial labs also have the resorces to put screening materials behind insulated walls, floors and ceilings and to employ special techniques around window and door openings. These techniques are simply too time consuming and expensive for most people to use in a domestic shed type environment. The standard insulation tests for floors using heavy, sharp, pointy objects with high voltage applied are just not practical for a shed, the floor would collapse under the stress. It is quite feasible to build a Faraday cage in a room or shed within a domestic environment. It will be inherently unsafe to work in the shed with live equipment exhibiting certain fault conditions unless additional precautions are taken to ensure that no contact whatsoever can be made with the screening material. Floating power supplies are a requirement due to the need to maintain isolation of the interior of the cage from the outside conditions. None of these regulations are a statutory requirement in the UK but are based on best practice as identified by the IET (formerly IEE). My concern is to point out the safety implications and not dictate how the project is finally built. Under UK law, electrical contractors are not allowed to disconnect a customer's supply no matter how unsafe it may be. They can only advise the customer not to use the installation/equipment and advise the electrical supply company of the defects. The supply company can disconnect a supply, but rarely do so as long as they are getting paid. Mike G0ULI |
blocking radio waves
Joe wrote:
"I know there is a term for a room like this but I can not remember it..'' The term that comes to mind for me is "screened room". I`ve used them in shortwave broadcasting stations where they provided excellent isolation. They were constructed of ordinary copper windowscreen wire which solders well for good continuity. Sometimes the rooms were double screened with wire on both sides of the supporting structure. You`ve already been given the caveats on joints and bypassing every conductor which punctures the structure. That`s necessary. Best regards, Richard Harrison, KB5WZI |
blocking radio waves
Thanks everyone
The shack will be run off of solar power only and 95% of everything it it will be 12 volt. It will have a 1200 watt inverter to run different AC items as needed ( a soldering iron comes to mind) I plan on grounding the sheild (for lack of a better term) of the shack, to my lightning /RF grounding system. There is no way that I would not ground the hell out of something like this. I use LMR 600 and 400 for the coax runs. The sheilding does not need to be perfect, just good. thanks again.. joe KI4ILB |
blocking radio waves
The real problem in making a shielded area like you propose isn't so
much the material as the seams and wires. Connection between panels has to be virtually continuous, or you'll have very ineffective shielding no matter what material you use. You need a completely sealed box, floor and ceiling included, with no unbonded hole or seam larger than a very small fraction of a wavelength in size. Aluminum is hard to bond well, so that's a poor choice. Doorways are particularly problematic - make a visit to a local EMC lab to see what measures are typically taken. The sealing requirements become more stringent as frequency increases. An equally or even more difficult problem is getting power, telephone, and any other conductors through the shield without allowing unwanted signals to come in with them. Roy Lewallen, W7EL merlin-7 wrote: When I build my new shack, I was thinking about lining the inside of the plywood with something, before it is installed, that would block outside radio transmissions inside the shack. Mostly in the 2 meter range and higher. Would simple aluminum foil work? If so what frequency range could I expect it to work in? If not any suggestions on material? The cheaper the better. I know there is a term for a room like this but I can not rember it..faraday chamber? The shack will be 12 foot by 16 foot, right next to my 60' tower, with HF and 2m antennas on it. I have no idea how they will interact with such a building... Thanks Joe |
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blocking radio waves
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