What’s A Faraday Cage?

Written by on October 22, 2012 in Antenna Turns, Faraday Cages, LBA Products, Test Equipment - 50 Comments
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Ben and His Kite – Don’t Try This At Home!

Ben and His Kite – Don’t Try This At Home!

A Faraday cage (sometimes called a Faraday shield, RF cage or EMF cage) is a shielded enclosure formed by conducting material or by a mesh of such material.  The enclosure is like a sealed tin can; it keeps the electromagnetic fields inside, and blocks the entry of external electric fields and radiofrequency waves. Faraday cages are named after English scientist Michael Faraday, who is credited with their invention in 1836.

Quick history:   Although the development of the faraday cage shielding effect has been attributed to Michael Faraday, it was actually Benjamin Franklin in 1755 who observed the effect by lowering an uncharged cork ball suspended on a silk thread through an opening into a metal container.  He noted that the cork was not attracted to the inside of the enclosure as it would have been to the outside and although it touched the bottom, when pulled out it was not found to be “charged” by the touch. Thus, Franklin actually discovered the behavior of what we now refer to as a Faraday cage or shield.

Faraday’s famous ice pail experiments duplicated Franklin’s cork and can trial. He conclusively demonstrated the electrostatic shielding effect when he built the first formal Faraday cage in 1836. With it, he observed and documented that the charge on a charged conductor remained only on its exterior with no influence on the interior.  His Faraday enclosure was a room coated with metal foil. Faraday made high voltage discharges from an electrostatic generator to strike the outside of the room.  Using an electroscope, he demonstrated that the discharges caused no deflection when located inside the room. Since it did so outside, no response meant absence of an electric charge on the inside of the walls.

Quick physics: The operation of a Faraday shield is best understood considering a hollow conductor. Externally applied electric fields produce forces on the charge carriers (usually electrons) within the conductor, generating a current that rearranges the charges. The rearranged charges cancel the applied field within and the current stops. There are additional factors to consider when applying an alternating current, particularly one in the radio frequency (RF) domain. The walls of a Faraday box or enclosure only shield the interior from external electromagnetic (RF) radiation if the walls are thick enough to reduce skin effect penetration and any holes are much smaller than the radiation’s wavelength.

Applications: The usefulness of the RF Faraday cage is its ability to protect personnel, operating systems, sensitive test equipment, volatile materials, and other things from radio frequency waves.  For instance, in the hospital environment sensitive operating room instruments are protected by RF shields from the bombardment of environmental RF energy.  In research and test labs and industrial shops similar protection is often afforded by faraday enclosures similar to the LBA EMFaraCage® (http://www.lbagroup.com/technology/faraday-cages.php).

Technicians Applying LBA Room Shielding Systems

Technicians Applying LBA Room Shielding Systems

The security of wireless communications is often protected using the Faraday principle by shielding building areas and forensic test facilities with architectural materials such as LBA’s SM-10 shielding fabric or CPC-54  conductive paint (http://www.lbagroup.com/technology/emi-rf-shielding-materials-fabric-paint.php). Coaxial cable such as used for cable television, actually includes a continuous Faraday shield to protect the internal conductors from electrical noise and to limit external radiation of the enclosed RF. Finally, the military uses this Faraday cage technology for protection of defense equipment for both RF protection, and protection from electromagnetic pulse attacks.

Ironically, the technology can also be used for illicit purposes.  A shopping bag lined with aluminum foil acts as a Faraday cage assisting shoplifters to steal RFID tagged merchandise. Hackers can set up Faraday cage test cells for “black” development of wireless LAN intrusion tools, for instance. On the other hand, university researchers use faraday cages to study anti-hacking in a secure RF environment. An excellent example is the program at East Carolina University that utilizes a custom LBA EMFaraCage® Faraday box as discussed in Technical Note 127: Keeping Black Hat In The Box.

University “Black Hat” Test in an LBA FC-10 EMFaraCage® Faraday Cage

University “Black Hat” Test in an LBA FC-10 EMFaraCage® Faraday Cage

LBA Faraday cage solutions: The EMFaraCage® shown above is one of a line of innovative portable desktop Faraday cages developed by LBA for production testing, laboratories, and other applications. Many other RF shielding requirements may be accomplished through LBA designed Faraday cages of architectural shielding materials. We design and furnish RF cages integrated into room or building construction using the most effective RF fabrics and RF conductive paints. We can also furnish architectural shielding solutions against EMF effects of nearby power lines, such as found in utility telecommunications sites.

For assistance on shielding system design, or to purchase EMFaraCages® or shielding materials, contact Byron Johnson at byron.johnson@lbagroup.com or at 252-757-0279.

 

50 Comments on "What’s A Faraday Cage?"

  1. Lt Col William B. Cheney, III, CAP November 1, 2012 at 1:50 pm · Reply

    A Faraday cage or Shield is a way to isolate componets from RF energy or to contain High Intensity RF such a a Broadcast Transmitter tube. The point is that it efficiently blocks RF energy. ln

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  2. Elmer Croan November 2, 2012 at 11:50 am · Reply

    I see a lot of people asking this question lately, and if you are having a problem with RFI then it could be useful, but an easier way to solve the problems with RFI in many cases is just insuring the grounding is correct and as close to 1 ohm as possible as well as filtering the power leads as usually this is where RF gets onto the back-planes from and mixes with the various circuits. If you are interested as one instance I saw of trying to shield your equipment from an E-Bomb or Coronal Mass Ejection (CME) as many survivalists or prepers are discussing then you are wasting your time, and money. The amount of energy would most likely be too excessive for anything but a purpose built grounding system to handle. Filtering a few millivolts of RFI as is the case in most EMC Testing is a lot different than trying to bleed off the energy from either lightning or an e-Bomb. In fact the Faraday Cage could actually become a safety hazard if it absorbs more energy than the grounding system can handle it will actually act as a very high power storage device like a huge Capacitor.

    The Lightning Protection systems used by Cell Sites is entirely different than the National Electrical Code or NEC most buildings are built to comply with, and exceeds it in many important ways such as no connections that are not exothermic or CAD welded. The ground rods are also significantly different (Lyncole) as well since they are drilled into the ground and are approx. 5 inches in diameter.

    I know lots more detail than you probably need, but given I have seen lots of people asking about these lately I can not be sure of your application or requirements. This is to say their is very limited real need for a Faraday Cage except getting rid of RFI in a very high radiation area such as adjacent to a High Power Broadcast Tower or in EMC testing were an absolutely RF quiet zone is needed. The National Radio Astronomy Lab has a whole valley where a RF Quiet zone has been built for just such a purposes so yes there are valid needs but I doubt most people really need them.

    I have solved lots of RFI problems by just checking the grounding and seeing it was too high when checked with a Megger or an Ohm Meter designed for testing soil conductivity under higher voltages than the 1.5V a typical VOM outputs. Induction is also such a problem on power leads that many manufactures take great care in data-center applications to physically separate power cables from data cables. I would try all of this before going to the expense of building a Faraday Cage.

    Elmer
    KF5RUK
    ln

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  3. Roland Richter November 2, 2012 at 11:51 am · Reply

    Lawrence, I could have probably used help from both you and Elmer a few times in my life dealing with station studio operations co located with transmitters…particularly FM. My worst problem was at a station in Beaumont where a 1 kw AM had a two tower directional right outside the building with the antenna for a 100 kw FM on one of the towers with the center of radiation of the FM only 240 feet high. RF was in everything. The problem there was often too much grounding…there were ground loops everywhere. Finally got each studio to “float” then grounded them from one point centrally. I was young in those days and had to learn the hard way that for 95 mHz RF, a wire is not a good ground connection because of the inductance and ended up having the boss buy a lot of 4 and 6 inch strap. At least we got all the buzz out of the mike channels and the cartridge machines were no longer stopping erratically! The telephone system was another whole problem. That was a long time ago and we did not know a lot about RF and humans, but I wonder just how safe that whole thing was for all of us working there. After that I discouraged anyone collocating that kind of stuff with studios…It was already in place when I went to work there.

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  4. Karl Schenk November 2, 2012 at 1:31 pm · Reply

    A Faraday cage is the one place at work where your cell phone won’t ring. ln

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  5. Jeremy Howard November 2, 2012 at 1:42 pm · Reply

    Ahh yes, a tried and true friend in a high voltage and high RF environment like we have here on Mt. Wilson. I have used variants of the principal in everything from analog exciters (so you could actually tune the thing while it was on the air and not get blown out by the klystron humming happily along three feet away) to generator transfer switches.

    A tool every RF guy or gal should have in their toolbox. ln

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  6. Allan Johnson November 5, 2012 at 9:53 am · Reply

    I remember the first radio shop was one for the AM directional just outside the back door. The AM moved out of town and the computer network moved into the shop creating the noise again. The flood ended it’s usefulness but it was a nice quiet place to test audio and rf gear. ln

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  7. Eduardo Cappia November 5, 2012 at 9:54 am · Reply

    Sometimes the Faraday Cage is responsible for increasing the RF internal noise in áudio equipamentos. This way we did it with a key that Is able to connect or not to the ground dependable on the results. Anyone did the same? ln

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  8. Brian Walker November 5, 2012 at 9:55 am · Reply

    If only I could put my office in a Faraday cage, I could get a lot more work done… ln

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  9. Karl Schenk November 5, 2012 at 9:56 am · Reply

    Yep. I worked in 2-Way radio for a while, and we had a “screen room” that was a simple Faraday cage about 8 feet to the side. We tested transmitters in there, using dummy load antennas, to avoid annoying the techs who were aligning receivers.
    It had two layers of screen, the outer layer grounded and the inner one isolated. The only RF leakage was through the power line, and that was minimized with a filter. ln

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  10. Lt Col William B. Cheney, III, CAP November 5, 2012 at 11:18 am · Reply

    For sure, good grounding of all equipment, antennas, and towers or masts is essential. And that means bare metal to metal contact. Number 6 or Number 4 wire or even better grounding straps can solve a whole host of problems.

    In Charleston, many broadcast radio antennas were built into the marsh to ensure good grounds.
    And its not enough to just set them up, connections need to be conductivity tested about once a quarter, and remade once a year. ln

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  11. Elmer Croan November 5, 2012 at 11:18 am · Reply

    Roland certainly one of the first things people thought of once the private sector started using Microwave instead of buried cables was to use a Microwave Radio for a Studio Transmitter Link just to get the Studio as far from the Transmitters as possible. It is unfortunate that many in the early days of Radio didn’t have this luxury, and Faraday Cages were needed. Today the best and often cheapest solution is just move the Studio to a location that makes more sense for business access, and place the transmitter as far away in a rural area as possible so the near field effects are of less concern to fewer people. ln

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  12. Lt Col William B. Cheney, III, CAP November 5, 2012 at 11:20 am · Reply

    The old HeathKit HW series came with a faraday shield over the finals.
    A Faraday cage room with two layers of counter valent mesh screen is no cheap item and is usually found in an RF labatory where total isolation to develop Signal to Noise ratios is essential and design reduction of transmitted sidebands require transmitter testing for long periods.

    It is only needed where you need complete control of the RF enviroment. Or as pointed out above, to need to isolaate people and equipment from a high level RF Energy Field. ln

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  13. Tim Hague November 5, 2012 at 11:20 am · Reply

    I was involved in designing a Faraday Shield for use in a hospital, we had to take a side room and totally isolate it from the EM environment, >70db to 3 GHz. We used the new copper (at that time) fabrics on the walls, isolated all the plumbing and services, filtered all power and data lines, shielded the windows with mesh embedded glass and ensured all surfaces were bonded together, took a standard hospital door, put a shield through the door, finger stock on the door edges. The finger stock was the only outward sign that it was a controlled environment. We met the specification. The room is used for monitoring brain wave patterns on stroke victims. A really interesting project. ln

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  14. Elmer Croan November 5, 2012 at 11:29 am · Reply

    Tim that sounds like it was a lot of fun, and it sounds like you
    accomplished a really RF Free Zone which makes me curious about the
    specification. Ii would.like to ask if you know why the 70db was needed.
    Was the objective to shield the patient from the effects of the RF or the
    measuring sensors and processing equipment?

    I am just the curious type and was wondering if you knew why the 70db.

    Elmer

    KF5RUK /AE
    ln

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  15. Roland Richter November 5, 2012 at 11:29 am · Reply

    Elmer:
    You are right about the split site situation being the best. Some of these small stations just could not afford having two separate pieces of real estate. In some cases, as long as it took me to get paid for some projects, I wonder if they could have afforded the microwave gear. Some of these guys were really on the air on a tube and a prayer! ln

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  16. Lt Col William B. Cheney, III, CAP November 5, 2012 at 11:29 am · Reply

    70 db is the Military specification for the rejection of unwanted RF. It has become pretty much a standard. Amateur Service requires only 40db rejection. ln

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  17. Elmer Croan November 5, 2012 at 11:30 am · Reply

    Roland I can see your point about the money issues …as they say necessity
    is the mother of invention. LOL!

    It have been over 35 years since I last saw a Low Frequency Antenna
    nicknames”The Dinosaur Cage” and I am not sure what they were used for
    since my HF,VHF, and UHF training was limited to the shipboard side with no
    ground station training except in SHF Satellites. The antenna looked
    exactly like the nickname a series of 12 to 15 poles in a circle with wire
    stretched between them. I found pictures on Google Earth of the one
    abandoned in Panama. It wasn’t to my knowledge LORAN because everyone of
    those I have is just a single tower. The antenna in question put out such a
    strong EIRP that for personnel safety the automobiles parked nearby were
    required to be grounded otherwise the charge that would build up during a
    standard shift on the car was enough to knock you out when you reached over
    and grabbed the car to unlock it and drive home. There were signs in the
    parking lot but frequently visitors would disregard when thinking they
    would only be a few minutes and once returning got an unpleasant surprise
    as they entered their vehicles. I hope to find on one of the either
    Veterans Websites a Navy or Army Tech who worked on one of these, or maybe
    some Ham knows what it was as those poor guys I am sure had to work in a
    Faraday Cage, or at least the Operations Room had to be one. Any ideas what
    frequency and or power that thing put out?

    Elmer

    KF5RUK /AE
    ln

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  18. Tim Hague November 5, 2012 at 11:41 am · Reply

    Hi, we’ll to be honest the spec was based around what we thought we could
    achieve, screening using materials rather than pan or sandwich aluminium
    construction is always difficult.

    When you are looking at brain wave patterns in coma patients interference
    from external sources can mask what you are trying to see.

    We also do standard cages with 100dB isolation up to 18 or 40 GHz, some can
    do 140dB in tempest applications.

    Best regards, Tim Hague
    Skype m0afj.Tim
    ln

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  19. Elmer Croan November 5, 2012 at 11:42 am · Reply

    Tim if I understand what you are saying
    it is that the signals are so weak from the patient that any
    background radiation picked up by the sensors could mask the
    signals you are looking for so you are doing this purely to
    improve the Signal To Noise Ratio (SNR) on the instruments used
    to detect the signals. If that is the case I can see how even 70db
    might not be what you are looking for. I don’t know if you have
    ever seen the detectors they use for sub-atomic particle research,
    but they are looking at such a weak signal they basically look for
    an old abandoned mine so they can get at least a couple of Km.
    below the surface since the particles they are looking for are not
    affected by this depth they can remove all other noise sources
    from the surface. Really the boundaries of science here, and
    certainly not what most of use have used Faraday Cages for.

    Thanks again for sharing all this great information. I am an
    Engineer first, but a self confessed Science Junkie. In my
    Satellite Communications days I have experience with Low Noise
    Amplifiers (LNA’s) such that in order to get the SNR needed we had
    to cool the electronic to about 14 degrees Kelvin, but the newer
    technologies have improved so much that this is no longer
    necessary, and GAs FET’s, and much more reasonable temperatures
    (noise and ambient) have made the communications much more
    reliable will much cheaper components.

    73

    Elmer

    KF5RUK /AE
    ln

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  20. Lt Col William B. Cheney, III, CAP November 5, 2012 at 11:44 am · Reply

    ELF is used to contact submerged submarines. There is one antenna stateside that I know of that was the target of several lawsuits back in the 80s. I think it was in WI. ln

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  21. Elmer Croan November 5, 2012 at 11:44 am · Reply

    William I thought I might share this
    little experiment we did with the metal they build the Faraday
    Cages out of that you speak of. I am not sure if the stuff you are
    talking about has air-holes or not, but the stuff we used didn’t
    so you usually just used it between two items on the circuit board
    you wanted to isolate.

    Anyway my friend who is a brilliant guy with a Phd. in Chemistry
    and works at one of the major Universities on staff is an Amateur
    Speaker Builder, and decided he was going to upgrade the fidelity
    of his 17″ TV back a few years ago when they still used Picture
    Tubes. He first looked at the very small magnets, and concluded
    this was the problem with the limited bass from the small speakers
    built in. Then he order so really high end speakers from Germany,
    and waited fort hem to come in, and he was so excited he called me
    to let me know he was going to change them out, and I should come
    check out the sound. The project was complete by the time I
    arrived to see or rather hear the results. I was wondering why he
    had a puzzled look on his face when he answered the door when I
    asked him how it sounded. He answered it sounded great, but the
    picture now was good. He wasn’t aware the magnetic field from the
    bigger speakers magnet would interfere with the electron beam used
    to scan the front of the screen so that the colors would be
    shifted. We were able to build a wall between the speaker &
    the picture tube, and luckily no permanent damage was done so we
    didn’t have to degauss the picture tube as this is really a last
    resort to restore the magnetic field of the picture tube. The
    older picture tubes for color we so sensitive to this that in some
    instances if they were reoriented from a North-South Facing to a
    East-West facing orientation you might see issues with the
    picture. Just one more reason we should be glad the industry is
    switching to DLP,Plasma, and LCD/LED technologies which are more
    immune to this effect. ln

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  22. Lawrence Behr November 5, 2012 at 11:45 am · Reply

    Thanks for all the great comments on faraday cages! As you see from the comments, they do come in all shapes and sizes for a wide range of purposes. For those wanting to read a bit more about shielding and interference, there are several informative technical notes at http://www.lbagroup.com/wireless_university.php.

    Col. Cheney, the sub comms antennas are a great subject! Back in the ’60′s, I was in charge of Pacific transmit antennas for the Polaris fleet, and was part of the project team for airborne 20 kHz transmissions. We used Super-Constellation aircraft packed with transmission gear and a five mile long antenna. Boy, did we have fun!

    K4JRZ

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  23. Elmer Croan November 5, 2012 at 11:45 am · Reply

    William I know what that antenna looks
    like, and the location you mentioning is not where the ones I have
    seen are at. The one on the West Coast is in the Pacific Northwest
    in the Cascade Mountains but not in a very well traveled area, and
    there was one in Hawaii as well in a Private Mountain Pass strung
    between two mountains just as the one in Washington is.

    The “Dinosaur Cage” was something else since there was one even in
    Panama I doubt it was for the Submarines. The ELF Antenna used to
    talk to Submerged Submarines is actually Much Larger since the
    frequency they use has a wavelength of several miles even a
    quarter wave antenna would be really huge. Much bigger than the
    Dinosaur Cage which I suspect was probably some kind of Ship To
    Shore M.F. link.

    73′s

    Elmer

    KF5RUK /AE
    ln

    Ex-Navy ET (Ship to Shore, Ship To Ship, Ship To Aircraft, as well
    as Satellite Communications)

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  24. Tim Hague November 5, 2012 at 11:46 am · Reply

    Hi Elmer, I’m surprised that your friend didn’t know the effects of magnetics to CRT’s, in the old days magnets were used external to the CRT to help focus the electron beam. I worked on the early projection TV’s which used this principle.
    I know people are glad to get rid on CRT technology but when set up ell they produce a better picture than flat screens and do not produce the amount to RFI that a plasma set does.
    ln

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  25. Elmer Croan November 5, 2012 at 11:47 am · Reply

    Tim you make good points about Plasmas,
    and I was never a fan of them. I avoided them in my applications
    in Telecom as much as possible because they also suffer from a
    Burn In Issue the gamers identified, but we identified it in
    Network Operations Centers at least 20 years ago because of
    displaying a US Map, and overlaying data on top. The picture
    started after awhile have permanent ghost images. I have always
    been a bigger fan of projection, and I myself use a DLP at home. I
    know there are issues but he last generation before Samsung
    shifted away from them were really good as it used the 5th
    generation TI DLP’s which had a much better contrast ratio due to
    tweaking of the mirrors deflection capabilities so they could be
    masked better to eliminate residual light when a pixel was
    supposed to be off. .

    My friend was a Chemist and not an Electrical Engineer, and as
    such was unaware the Electron Beam that scanned the phosphorus was
    driven or aimed by a magnetic field which was controlled by
    windings around the yoke of the picture tube. I actually showed
    him the windings in the yoke assembly when we had the set opened
    up, and he instantly understood a magnetic field anywhere nearby
    would be problematic. We laughed after we got it corrected, but
    was a tense situation until we got the shield built because the
    picture really was distorted.

    Good times !! LOL !!

    We talked after we fixed the set and while having a beer I told
    him of some interesting stories about a time in the US Navy about
    people permanently magnetizing their wrist watches by getting too
    close to a magnetron. I still to this day wear very little if any
    jewelry, and once I explained it to my wife she prefers that I
    don’t wear a ring either since she prefers my hands aren’t
    disfigured by burns. I wear watches, but out of habit the instant
    I get near any electronics it goes off the wrist, and into my
    pocket. I also learned in the US Navy that hand needs to stay
    there as well or behind your back when around high voltages.

    The usage of the human body to complete a circuit is something I
    usually don’t recommend as the one time I took 220V (defective
    safety ground) from one arm to the other it popped by shoulders
    out of socket so hard I was speechless, and my lab partner thought
    my inability to speak meant my heart stopped and I needed a punch
    in the chest which was not needed to restart my heart but it did
    serve the purpose to relocate my shoulders so that the words I was
    attempting to say ended up being the first thing I screamed when
    they relocated which was “DON’T I AM OKAY” followed by “Oh Crap !
    that really F%$#ing hurts” I really did cuss like a sailor for a
    few seconds after regaining speech….LOL !!! I now know why they
    told us one hand behind your back. Weeks later I tried not to
    laugh when this real gung-ho guy who always wore his Dog Tags even
    though we weren’t required to stateside, and even if we were they
    told us to remove them when working on energized
    electronics….Anyway he was working on this VHF/UHF Transceiver
    with the PA Finals exposed making a measurement on the tubes when
    his Dog Tags fell out of his shirt into the High Voltage Power
    Supply which made a really nice burn around the back of his neck
    where the chain holding the dog-tags touched him completing the
    circuit to ground via his human flesh.

    I guess I should have posted the previous paragraph as a Public
    Service Announcement PSA or to the hazards of working on radio
    Equipment that is energized…LOL !!!

    73′s

    Elmer

    KF5RUK /AE
    ln

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  26. Elmer Croan November 6, 2012 at 11:15 am · Reply

    Lawrence I would take it the stuff you worked on for the Polaris is pretty much unchanged till today then? The other issue is I understood that the antenna is several miles long as would be the case with what I saw in Hawaii up in a mountain pass strung between to mountains, so what is the Dinosaur Cage that is a circular antenna about 300 feet? I found the one in Hawaii that I had been up close to in the 1970′s and like the one I previously found in Panama it was abandoned as it had no visible staff in any of the support buildings unlike the nearby Satellite Dishes. I wasn’t sure if Panama was abandoned for other reasons, but it would see the same configuration was also abandoned in Hawaii.The SHF Satellites orginally used in the DSCS or Discus Project were only able to communicate to shipboard terminals on larger ships such as Aircraft Carriers, and the advent of newer Phased Array Antennas improved on the fast tracking that was almost impossible for a dish in a dome. The advent of a Fleet Satellite Communications System FSC-79 using a UHF Satellites and smaller ships being able to reliably communicate to shore bases without the need for MF & HF Communications probably expedited the retirement of some of the older systems such as the one using the strange Dinosaur Cage Antenna. If you look at the Naval Communications Station near Whitmore Village in Oahu Hawaii you will see three antennas in a triangle with two pointing one direction which is the FSC-79′s for FLT-SATCOM and the one point a different direction if the FSC-78 which was initially used for the old Defense Communications Agency DSCS Phase 2 satellites which were SHF. I do not know if this is a relay to other shore-bases as they have these in the USA on the West Coast as well as Guam & Japan.
    I know in a Ham group the subject of Navy abandoning MF & HF for Satellite probably won’t win me any friends, but for the exact same reason we use those frequencies as a hobby, and require a constant adjustment to how propagation performs from day to day this is the exact reason the US Navy probably moved away from these modes of communications. I still as a historian of radio Communications would like to know what frequency the Dinosaur Cage was used for and if there is a formal name for that type of antenna. I have pondered over the years if these were just 8 or twelve dipoles aranged together in a circle with each one having a different orientation so the operators can switch between them to effectively steer the direction of the antenna without any moving parts that would be problematic in climates that experience high humidity and hurricane force winds such as almost any US Navy base would be expected to experience. Let me know Lawerence if you need help finding the Dinosaur Cage as it is just to the left in Google Earth to the Satellite Antennas at the Naval Communication Station.

    73′s
    Elmer
    KF5RUK
    USN-ET
    ln

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  27. John Marshall November 6, 2012 at 11:16 am · Reply

    There is a VLF station is Jim Creek Naval Radio Station, Arlington, Washington. The station is in a valley with the antenna streached across the valley from two mountain tops. Amateur radio operators have toured the facility. It is also a RV camping facility for the military. The facility can be seen on Google Maps. ln

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  28. Elmer Croan November 6, 2012 at 11:17 am · Reply

    John is road below the antenna in the one in Washington State open to the public? The one in Hawaii is on Military Land and although you can access it from the other side of the Mountain it is a restricted area for only Military , and since the raod is accessed from Scofield Barracks it is not open to the public as a Navy Base is on the other side of the mountain making it impossible to get to the antenna. I am not sure you can see anything from Google Earth. How long is the cable itself that is strung between the two mountains?

    Elmer
    KF5RUK
    ex-Navy ET
    ln

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  29. John Marshall November 6, 2012 at 11:17 am · Reply

    The site is only open to the military. This is a wikipedia link: http://en.wikipedia.org/wiki/Jim_Creek_Naval_Radio_Station
    Navy link:
    http://www.navylifepnw.com/site/67/Jim-Creek.aspx

    Harold E Holt:
    http://en.wikipedia.org/wiki/Naval_Communication_Station_Harold_E._Holt

    Cutler Maine:
    http://en.wikipedia.org/wiki/VLF_Transmitter_Cutler

    I was chief engineer at an AM station at Drayton Harbor, Blaine, Washington. Nearby at Birch Bay was an over the horizon radar Air Force Base. It was work keeping the radar signal out of the AM station. Just a little further away at Custer, Washington was an FCC monitor station. ln

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  30. eric smitt November 6, 2012 at 11:18 am · Reply

    The “Dinosaur Cage” you refer to is a Wullenweber receive antenna used by the military as a direction finding array, made of minopole verticals with a “cage” reflector behind it (100 feet tall). All verticals are fed to a rotating switch, called a goniometer, that takes the radio wave approaching the verticals and sums up the signals to give very high gain in the direction the switch is “pointed” to. The antenna is actually 2 sets of monopoles, the low band array, and the high band array, which uses smaller vertical monopoles (more of them), a smaller reflector cage, but is a larger diameter. When I worked with these arrays (in the late 60′s) I think the diamater of the cage was 1000 feet. The directional receive gain was in the order of 32 dB from 2 to 32 MHz. They were located all over the world in the HFDF program, which has since been declassified. ln

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  31. Elmer Croan November 6, 2012 at 11:27 am · Reply

    John thanks for all the information I
    have already been looking at the Jim Creek Facility on Google
    Earth. I can’t see nearly as much detail on Google Earth in the
    Hawaii location. I might need to reexamine Hawaii now that I know
    what I am looking at.

    I am really interested in the OTH Radar being a Radar Person
    myself. I have no experience on this kind of stuff as wondering if
    the US Version was as bad as the Russian Woodpecker or if your job
    was a little easier than getting rid of that constant chatter.
    What kind of frequencies were you concerned about or was it just
    so strong it bleed into everything including the power cabling?

    73

    Elmer

    KF5RUK
    ln

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  32. Lawrence Behr November 6, 2012 at 11:28 am · Reply

    Elmer,

    The “dinosaur cages” were indeed DF arrays, receive only.

    The high power LF in Hawaii was 600 kw and used a five tower flat top array at NAVCOMSTA Lualualei. At the same site was a variable frequency NORD LF 100 kw array that was used in the Polaris program. These were relatively broadband and similar NORDs were located in five places around the Pacific. One was also at Annapolis. All have been decommissioned and removed, I believe. Informally, we used the NORD at about 50 kHz for pioneering SSB communications to a receive station in Kodiak, Alaska. This was unheard of, and generated great interest in the Navy, but disappeared after a few years and I’ve heard nothing more since. Possibly because no antenna, to my knowledge, has ever been able to match the bandwidth of the NORDs, and they went away with the cold war.

    Just a note on HF. Several of the Navy chiefs were hams, as I was. We set up a ham station using transmitters there with big rhombics (legal power, of course). We piped in the receive end from other rhombics at a receive site near Schoffield Barracks. We had a ball being the only signal on dead bands. We ran virtually a 24/7 20 meter link with some other COMSTA hams with a similar rig near Washington, DC. It was hot. Official excuse for the lash up was a MARS station, and a deal of MARS traffic was linked into Vietnam on the MARS frequencies… ln

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  33. Elmer Croan November 6, 2012 at 11:31 am · Reply

    Lawrence thanks for the information, but I got to disagree with the Dinosaur Cages being receive only as my previous post stated we had to ground your vehicle while inside the control rooms in the center of the cage as it would collect E-Fields from the transmitted EIRP which was quite large. I saw the facility at Lualaulei when we drove thru the pass between Schoffield Barracks. The Dinosaur Cage in question was back at NAvCamsEastPac which is North of Whitmore Village. Do you know of anything else that could have used a Circular Antenna and transmitted? ln

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  34. eric smitt November 7, 2012 at 4:39 pm · Reply

    Elmer, I worked on the Wullenweber System. It was receive only. I don’t know why you had to ground your vehicle, but it may have upset the receive pattern of the array. The Goniometer (RF Switching System) was a capacitive coupled switch that had a power limitation of less than 100 mW of power. All coax cable to the elements was phase matched triaxial cable, phase matched to within a tenth of a degree at the highest frequency of interest. Inside the goniometer switch (which was driven by a servo-motor) 17 elements were combined. The center element had a delay line inserted. The next to center elements had a slightly less delay line. The next element set had a slightly lower delay line, until you reached the last elements. Then all the signals were added together, as a reinforced signal, in phase. This system could not take any power. It was receive only. The goniometer was located in the exact center of the array circle.
    73,
    Eric K9ES
    ln

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  35. Lawrence Behr November 7, 2012 at 4:39 pm · Reply

    Elmer, I don’t know that there weren’t some other antennas that physically looked like Wullenwebers for OTH radar, etc. There are also some structures similar to those used for EMP testing, not communications. I can’t think of any reason why there would be high RF fields inside a receive array. More at http://en.wikipedia.org/wiki/Wullenweber.

    Relevant to the faraday cage note, I understand that the control/receiver areas of these arrays were heavily shielded to contain secret traffic and prevent unwanted RFI intrusion. The main purpose of these, as I recall, was to support Naval intelligence in monitoring Russian sub movements, so everything was considered very sensitive. I think typical faraday shielding was similar to today’s TEMPEST standards, around 100 dB or so.

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  36. Elmer Croan November 7, 2012 at 4:40 pm · Reply

    Lawrence I indeed was getting the Lualualei Transmitter confused as far as the whole induced E-Fields was going with the grounding the car. Looking at the pictures jogged my memory on Lualualei being the High Power Transmitter. The description of the Dinosaur Cage being a D.F. more closely fits the units duties that ran ours at NavCamsEastPac or N.C.S. Honolulu as it was know previously. It’s funny how after reading the descriptions then looking at the pictures I can see myself driving thru Lualualei those many years ago. I only drove by the Dinosaur cage a handful of times since there was a looping road that meant the Satcom Site could be accessed by driving either way on the loop, and the other way that avoided the Dinosaur Cage was the shortest.

    Again thanks for all the information, and solving my decades old question. Did the Keyhole or Big Bird Satellites make these no longer needed so that’s why the one in Hawaii is abandoned?
    ln

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  37. Elmer Croan November 7, 2012 at 4:40 pm · Reply

    Eric I thanked Lawrence, but left you out. I appreciate the help you gave as well on identifying this really interesting system. I am getting distracted looking at all these pictures of the old bases I was stationed on. LOL ! I am really starting to rememeber driving around on the bases, and as I said above I was actually over on Lualualei when I saw the grounding hookups for the cars. It’s has been 35years so it took a few looks at the pictures to remmeber I was actually on the other base so it couldn’t have been the Dinosaur Cage so you are right there probably wasn’t a hook up near the Wullenweber. Again thanks for all you help. ln

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  38. Jacek Krzywicki November 7, 2012 at 4:42 pm · Reply

    The link is very interesting, but the discussion and comments shared by the other visitors are truly fascinating. I personally enjoyed some of the historical anecdotes. ln

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  39. michael November 9, 2012 at 2:12 pm · Reply

    Thank you for the explanation I always thought a faraday cage was where he kept his budgie

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  40. Charlie Cunningham November 13, 2012 at 5:15 pm · Reply

    I’m a little surprised that there isn’t more mention in this thread of employing Faraday Cages to defend against High Voltage and ESD hazards! The focus here seems to be almost exclusively on RF shielding. Charlie, K4OTV ln

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  41. Elmer Croan November 14, 2012 at 9:20 am · Reply

    Charlie you make valid points, but given the LinkedIn Group you are posting
    this on I would expect the focus to be mostly RF Interference which is from
    induced currents the same the two issues you mention. The internal designs
    of many transceivers (mostly HF due to higher powers) utilize small Faraday
    Cages to shield the components inside. Microprocessors and other Logic
    Circuits could experience data transfer issues resulting in errors so they
    are also important. I believe everyone was aware of these transceiver
    issues as someone previously mention the Power Amplifier (PA) are many
    times shielded. I am unsure of your reference to High Voltage so please
    expand on that unless you are talking about protecting the low voltage
    circuits from the induced fields inside switchgear cabinets.

    I believe we have for the most part covered all the valid applications for
    Hams even the one I personally feel is getting too much hype which is from
    “preppers” to shield from an eBomb or the effects of one I feel which is
    more valid a threat to general public which is a Coronal Mass Ejection
    which is not really a threat you need a Faraday Shield but some backup
    power. The question I first saw asking about Faraday Cage was posted in
    response to something a “prepper” told someone about these two issues.

    Elmer

    KF5RUK /AE
    ln

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  42. Phil Chadwick September 3, 2013 at 2:31 pm · Reply

    “The walls of a Faraday box or enclosure only shield the interior from external electromagnetic (RF) radiation if the walls are thick enough to reduce skin effect penetration”

    That’s true for RF, but for lower frequencies such a cage will shield the electric field component whilst not doing a whole lot for magnetic, even when very thin. Because it’s an isopotential (or, if you like, because Maxwell’s equations require it at the boundary of a perfect conductor).

    A good example is live-line working, when power workers go in close to 400 kV 50/60 Hz lines wearing conductive suits. The immediate risk from the high E-field is removed (and in fact they connect themselves electrically to the line to stop the corona discharge) but they still have to show compliance with magnetic field limits since the B field goes right through the suit, as you say. ln

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  43. Greg Alberti September 3, 2013 at 2:31 pm · Reply

    http://www.youtube.com/watch?v=9tzga6qAaBA

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  44. LBA September 16, 2013 at 9:50 am · Reply

    Good point. Low frequency magnetic shields generally require ferrous metals to be effective.

    -LB

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  45. Tim Kridel November 21, 2013 at 10:51 am · Reply

    Some trivia: When Eddie Van Halen built 5150, his home recording studio, he had to enshroud the entire facility in a Faraday cage made out of chicken fence because his gear was picking up a nearby AM station. ln

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  46. Mary Christine Erikson November 21, 2013 at 10:52 am · Reply

    hee hee, 5150 the police code for a nutcase.
    ln

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  47. Tim Kridel November 21, 2013 at 11:31 am · Reply

    Yup. Ed got the name from his engineer, Donn Landee, who heard it on his scanner. And to bring this back to ham radio, 5150′s original console had preamps designed by WA6PUK (SK). ln

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  48. Mary Christine Erikson November 21, 2013 at 11:37 am · Reply

    love the tutorial. holes smaller than wavelength – so use a total surface no holes and it protects, if thick enough, against all frequencies, right?

    what would happen if the electrostatic discharge was done INSIDE the faraday cage? charge the walls and get a shock?

    does conductive paint come in all colors? I would have a major problem at home if I painted the inside of a room something other than the original color (blue). Does it dry hard or some different texture than normal paint? ln

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  49. Wes Brodsky November 22, 2013 at 10:12 am · Reply

    I am a volunteer at Boston’s Museum of Science. Follow this link to see a very convincing demonstration of a Faraday Cage:

    http://www.mos.org/live-presentations/lightning
    ln

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  50. Cortland Richmond November 22, 2013 at 10:12 am · Reply

    Wes,I’ve been there (1980′s) and seen the Van de Graaf in action when I was living and working in Massachusetts; my son LOVED it. But you know, its only a Faraday shield if current on the surface doesn’t get inside; just drawing leaders to the bars is *cheating*. Heh! ln

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