The loss will be from dielectric loss, especially with asphalt shingles above. For RF loss purposes, not much difference between layered asphalt shingles and an inch, half inch, of dirt. Plenty lossy. Lay a dipole on an asphalt roof and explain the detuning and the widening of the SWR curve.
73, Guy ----- Original Message ----- From: "Jim Brown" <[email protected]> To: "Elecraft" <[email protected]> Sent: Tuesday, May 26, 2009 7:08 PM Subject: Re: [Elecraft] Dipoles and Heat > On Tue, 26 May 2009 18:06:03 -0400, Guy Olinger, K2AV wrote: > >>Probably the same as as a 50 watt light bulb, > > This seems wildly pessimistic. I'd guess no more than a dB or so of > dissipation. A typical dipole near resonance looks like about 70 > ohms, nearly all of which is a resistance that represents RADIATED > power, with the rest being wire resistance. So lets say that some of > that power causes current flow in nearby conductive objects. That > current will be small unless those objects are near resonance, and > whatever the current, it will cause more re-radiation than > dissipation, because those objects have radiation resistance too. > > 73, > > Jim K9YC > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
