Matt: Agreed that digging your own hole in the ground is a tad costly for creating RF shielding. OTOH, when the salt is removed from a mine, they don't back-fill it to delete the insult to Mother Earth. So, as the miners extract their economic interest, they move on, leaving access and big, relatively useless holes. To paraphrase Dire Straits; "Shielding for nothing and your holes for free."
Obviously, a hole in the ground may yield shielding, but it's very echoic. It's a long correlation to OATS conditions. My flash on the subject had to do with the myriad problems we have with the darn ground plane. We want it big but cheap, highly conductive but exposed to the weather, made up of repairable (or replaceable) pieces but electrically smooth and flat. There's not much cheaper in this world than water and salt. Combined into a conductive fluid, gravity (and the fact that the Earth is flat) pulls the fluid into a nice flat, smooth surface. Maybe the conductivity of the near-saturated solution is good enough to use by itself. Or possibly the salt water could be used to flood the existing mesh or plate ground plane to just a half-inch or so, where it would function to smooth the surface roughness of the underlying conductive metal. (We might need to provide some type of active galvanic protection to prevent corrosion.) I don't have any current need to investigate this idea, as I'm primarily involved in Military related EMC. But the cost/benefits seem very interesting, and someone may be able to follow up on it. (I'm visualizing those big, shallow salt marshes at the south end of San Francisco Bay. Or maybe someone has a computer routine for investigating OATS performance.) Ed :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-) Ed Price ed.pr...@cubic.com Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 (Voice) 619-505-1502 (Fax) Military & Avionics EMC Services Is Our Specialty Shake-Bake-Shock - Metrology - Reliability Analysis :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-) > -----Original Message----- > From: Aschenberg, Mat [SMTP:matt.aschenb...@echostar.com] > Sent: Thursday, August 05, 1999 6:17 AM > To: 'roger.vi...@wwgsolutions.com'; Lacey,Scott > Cc: 'Price, Ed'; 'emc-p...@ieee.org' > Subject: RE: cost effective EMC facility > > > I was under the impression that we were discussion the "Cost-effective" > emc > testing solutions, not the cost-absurd solutions. Maybe salt mines are > going > for a lot less these days. > > > -----Original Message----- > > From: roger.vi...@wwgsolutions.com > [SMTP:roger.vi...@wwgsolutions.com] > > Sent: Thursday, August 05, 1999 2:28 AM > > To: Lacey,Scott > > Cc: 'Price, Ed'; 'emc-p...@ieee.org' > > Subject: RE: cost effective EMC facility > > > > > > > > > > A very large EMC test site has been operating underground in England for > > some > > years. This is in Cheshire where salt is mined, leaving large > underground > > open > > spaces surrounded by absorbing salt-laden walls. The reduction in > ambient > > emissions is another benefit of this site. As an article in the UK EMC > > Journal > > reports (http://www.emc-journal.co.uk/archive1/980402.html) , it is now > > run by > > Celestica. > > > > Roger Viles > > WWG > > > > > > > > > > "Lacey,Scott" <sla...@foxboro.com> on 04/08/99 16:37:09 > > > > Please respond to "Lacey,Scott" <sla...@foxboro.com> > > > > To: "'Price, Ed'" <ed.pr...@cubic.com> > > cc: "'emc-p...@ieee.org'" <emc-p...@ieee.org> (bcc: Roger > > Viles/PLY/Global) > > > > Subject: RE: cost effective EMC facility > > > > > > > > > > > > Ed, > > > > I find your idea of a salt water ground plane very intriguing. I imagine > > the > > salts used would involve more than just table salt, and the chemistry > > would > > have to be checked and adjusted regularly, similar to a swimming pool. > The > > problem of stratification could easily be solved with circulator pumps, > > which would be turned off just prior to actual use (those of you near > > fault > > lines might take advantage of natural agitation, your salt water pools > > would > > be "shaken, not stirred"). : ) > > > > On a related note, does anyone have any experience doing EMC scans below > > ground? It seems that the earth would be about the lowest cost shielding > > material available. Perhaps an updated and enlarged version of the early > > pioneers "soddie" (sod hut) might be just the ticket. It might even > > incorporate a salt water ground plane. A side benefit would be that EMC > > engineers might gain some useful exercise by swimming a few laps at > lunch > > time (how many laps around the turntable/raft equals one mile?). : ) > > > > Scott Lacey > > > > -----Original Message----- > > From: Price, Ed [SMTP:ed.pr...@cubic.com] > > Sent: Monday, August 02, 1999 5:35 PM > > To: 'Arun Kaore'; 'emc-p...@majordomo.ieee.org' > > Subject: RE: cost effective EMC facility > > > > > > Arun: > > > > I was just struck by what you said about "setup a Sea Plane or a > > salt water > > based site" . Has anyone ever set up an OATS using salt water as > > the ground > > plane? Talk about excellent surface smoothness, easy to level and > > cheap > > material, plus simple repair! (Uhh, could we say it fixes itself?) > > > > Just what conductivity would be enough? Could we get enough > > conductivity > > before we reach salt saturation? > > > > I suppose the upper limit on surface area would be when we get to > > the point > > of the wind causing surface ripples. Or gravitational tides. > > > > Turntables might be a lot cheaper, too. Just a thin raft that > > floats. > > > > Seriously, has anyone tried this for an OATS? (I seem to recall the > > US Navy > > had a really big ship simulator here in San Diego, where they > placed > > scale > > models of ships on a sheet-steel "sea" in order to model HF wire > > antennas.) > > > > Regards, > > > > Ed > > > > > > > :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):- > > ): > > -):-):-):-):-):-):-):-):-):-):-):-):-):-):-) > > Ed Price > > ed.pr...@cubic.com > > Electromagnetic Compatibility Lab > > Cubic Defense Systems > > San Diego, CA. USA > > 619-505-2780 (Voice) > > 619-505-1502 (Fax) > > Military & Avionics EMC Services Is Our Specialty > > Shake-Bake-Shock - Metrology - Reliability Analysis > > > > > :-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):-):- > > ): > > -):-):-):-):-):-):-):-):-):-):-):-):-):-):-) > > > > > > --------- > > This message is coming from the emc-pstc discussion list. > > To cancel your subscription, send mail to majord...@ieee.org > > with the single line: "unsubscribe emc-pstc" (without the > > quotes). For help, send mail to ed.pr...@cubic.com, > > jim_bac...@monarch.com, ri...@sdd.hp.com, or > > roger.volgst...@compaq.com (the list administrators). > > > > > > > > > > > > > > > > > > > > --------- > > This message is coming from the emc-pstc discussion list. > > To cancel your subscription, send mail to majord...@ieee.org > > with the single line: "unsubscribe emc-pstc" (without the > > quotes). For help, send mail to ed.pr...@cubic.com, > > jim_bac...@monarch.com, ri...@sdd.hp.com, or > > roger.volgst...@compaq.com (the list administrators). > > > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to majord...@ieee.org > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to ed.pr...@cubic.com, > jim_bac...@monarch.com, ri...@sdd.hp.com, or > roger.volgst...@compaq.com (the list administrators). > --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
