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## RE: [RFI] Earth isolation

 To: "Jim Brown" RE: [RFI] Earth isolation "EDWARDS, EDDIE J" Thu, 9 Sep 2004 10:21:18 -0500
 ```You're correct Jim-- wrong word choice. "Characteristic Impedance" has a specific meaning in electrical theory related to transmission lines. My goof. That's why peer review for papers is so important! :-) On the last part, I disagree however. You've simply restated what I said except in one case. You have not disconnected anything when adding a choke (and you actually state this by noting the DC connection); you only change the impedance which is frequency dependant: Z=SQ RT[(R*R)+(X*X)] & X=[-wfL*(1/wfC)]/[(WfL)-(1/wfC)]. Note the "f" in each term. Now, at certain frequencies, other circuits that were higher in impedance before are now lower in impedance by comparison. That can lead to "ZAP!" 73, de ed -K0iL -----Original Message----- From: rfi- On Behalf Of Jim Brown On Thu, 9 Sep 2004 08:48:49 -0500, EDWARDS, EDDIE J wrote: >If you place the choke on the AC mains ground you WILL create a change >of that circuit's characteristic impedance Leave out the word "characteristic" -- it's not a transmission line. Just plain old series impedance. Now the sentence is right on! >and it will no longer >function as the AC safety ground whenever you need it. Yes >You also violate >the single point grounding principle since that circuit now sees other >grounds as lower impedances (like thru your equipment circuit boards or >through humans in some cases). Again, not the right words, but the right problem. The single point principle is violated because the choke disconnects the power system from the single point. And the system is unsafe because the choke blocks the required connection at the frequency of potential power faults (spikes, lightning hits, etc.). You DO see the connection if you measure it with a DC ohmmeter (or audio frequency bridge), but lightning and power spikes aren't predominantly DC or audio, most of their energy is at much higher frequencies. Jim Brown K9YC

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