You are confusing DC resistance with impedance. The impedance of a transducer (loudspeaker, microphone, headphones) is a combination of the dc resistance of the voice coil, the motional impedances, and a resistance that corresponds to the power converted to sound. Thus, those headphones that look like 72 ohms to you DC ohm meter look more like 150-250 ohms to an audio frequency source.
An antenna acts the same. If you were to measure the DC resistance of the wire that makes up your antenna, you might see an ohm or two, yet the impedance of the antenna may be anywhere from 10-20 ohms for a short mobile antenna to 40 ohms for a quarter wave vertical to 70 ohms for a dipole to hundreds of ohms for a longer antenna. Much of the difference is the radiation resistance, which is a circuit element that accounts for the power that is radiated. And, in both the antenna and the loudspeaker/headphones, there are reactances (L and C) that account for the resonances. In the loudspeaker/headphones they are mechanical resonances, where in the antenna they are electrical ones. Jim K9YC On Tue, 15 Jun 2004 21:32:40 -0700, Rick Dettinger wrote: >My Sony MDR 7506's have a DC resistance of 72 ohms per side. Since the >phones are in parallel, the rig will see about 36 ohms. _______________________________________________ Elecraft mailing list Post to: [email protected] http://mailman.qth.net/mailman/listinfo/elecraft You must subscribe to post. Subscriber Info (Addr. Change, Unsub etc): http://mailman.qth.net/subscribers.htm Elecraft page: http://www.elecraft.com
