[Elecraft] k2 audio power

[Jim Brown]

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.