Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: A DIY Faraday cage: caveats and hints?
    From: Brad Morris
    Date: 2019 Jan 22, 13:23 -0500
    As an engineer who has spent a goodly amount of time in an anechoic chamber measuring RF energy, some statements should be made:

    1) lightning strikes are more than the simple discharge of electrical energy.  They also produce a pulse of RF energy.
    2) Shielding your equipment from a direct strike will be a fools' errand.  No matter the insulating impedance, there will always be a discharge that will bridge the insulator, unless you get ridiculous.  You'll likely be fried yourself, but thank goodness your heirs will get your still good cell phone. Heh!
    3) Shielding your equipment from external RF energy is exactly equivalent to shielding your equipment from emitting RF noise. RF energy does not know direction.
    CONCLUSION: Multiple papers exist for the implementation of RF shielding in a commercial environment.  This is not lore, it is engineering.  The bulk of my experience in shielding is for the US military, among the best you can get. I can tell you frankly: Nothing is perfect, the RF energy is just attenuated to a certain amplitude.
    4) The RF energy in a lightning pulse is broadband noise, ranging in frequency.
    5) RF shielding must take into account the wavelength of the RF energy, as others have pointed out.
    CONCLUSION: Since we cannot predict what frequencies/wavelengths are produced, we cannot determine the minimum size hole permissible as a function of wavelength.  Therefore, we can rule out a mesh shield and must use a solid shield.
    6) We must know the energy level we wish to shield, in order to effectively define its characteristics.  Yet we cannot know the energy level of the RF strike as the proximity to the strike and the strike power itself are variable.  
    CONCLUSION: Whatever shielding you do apply, can and will be overcome by a closer, more powerful strike.
    7) RF energy crawls on conductive surfaces and not on non-conductive surfaces. 
    CONCLUSION: the better the insulator, the tougher it is for RF to bridge the gap. The higher the impedance, the better.

    So why should we bother?   It seems like we cannot protect ourselves from RF.  The closer, more powerful lightning strike will always overcome our feeble efforts.

    Some shielding is better than none.  A solid (not mesh) box with an excellent conductive seal (conductive grease/gasket) will go a long way in keeping RF energy out.  The energy that does sneak through (remember, nothing is perfect) must then be forced to bridge another gap, to wit, the internal insulator. The higher the impedance, the harder it is for the RF energy to crawl on the surfaces of your electronic equipment.  

    This is not a recipe for a 'perfect shield'.  Such a thing does not exist.  An imperfect shield is still better than sailing without a shield.  

    The better, common sense advice is to not go out on the water if thunderstorms are in the area and to get off the water as soon as you can.  Your fishing trip  joy ride can wait.




    On Tue, Jan 22, 2019, 12:18 PM Tony Oz <NoReply_TonyOz@fer3.com wrote:

    Frank, you say:

    Perhaps we need to commission a vessel to sail out into some thunderstorms loaded up with a few dozen variants on the Faraday cage concept to find out what really works.

    I volunteer to be a navigator on that boat! List me in if this project ever starts!




    60°N 30°E

    View and reply to this message

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site