And that my friends is why the broadcast stations have extended amounts of "sheet" copper tying everything to ground that should be. IMHO.
Mel, K6KBE ________________________________ From: Ron D'Eau Claire <r...@cobi.biz> To: elecraft@mailman.qth.net Sent: Friday, October 21, 2011 4:07 PM Subject: Re: [Elecraft] OT- Coax for ground wire? I think Jim accidentally reversed his meaning about ground lead inductance. Lowering the inductance of the ground connection does *not* lengthen the effective radiator or "add loss". Allowing the ground system to be part of the radiator by letting the ground lead have significant inductance and so add to the overall length of the antenna system may well increase losses and promote coupling to house wiring, etc. That's good reason to use a low-inductance ground connection. When running an end-fed wire as I do, it's useful to keep the rig chassis at a low RF potential. If the rig is allowed to have significant RF voltage on it (as when the feed point of the wire is near a voltage loop), the rig adds my body to the active antenna, changing the tuning. Also, significant RF voltage floating around the DC supply chassis (because it's connected to the rig) can do weird things to the voltage regulation if a junction in the regulator starts rectifying the RF. In my case the copper sheet terminates in an RF ground system that enters through the wall a few feet from the operating position, so extending the sheet to where it enters ensures that the entire copper sheet stays at a very low RF potential at all times, and having the sheet extend behind the equipment allows very short ground connections to each chassis, keeping everything at the same low RF potential. 73, Ron AC7AC -----Original Message----- On 10/21/2011 12:25 PM, Ron D'Eau Claire wrote: > For RF, you want the lowest possible inductance in the ground lead since > inductance has reactance and reactance is what you do*not* want. Yes, BUT -- the principal function of the EARTH connection is lightning safety. With any antenna that loads like a long wire and ends in the shack, the "ground" wire is part of the antenna unless it has been decoupled from the "ground" wire by a lot of radials that end in the shack. Further, the other end of that wire goes to lossy earth, and the equivalent resistance of the earth connection reduces the power that gets radiated -- UNLESS there are radials. Bottom line -- low inductance is important for lightning safety, but it's primary effect on behavior of a long wire antenna (including inverted L, Tee vertical) is to lengthen the antenna a bit and add loss. And yes, the braid of coax makes a nice ground conductor. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
