[TowerTalk] Q of coil Al vs Cu - Re: OT: Inductor Calculator

[jimlux]

On 2/28/19 11:05 AM, Jim Thomson wrote:

> 
> ## Forget Q  for a minute, thats  semantics.  Copper tubing is a helluva lot higher  Q  vs  aluminum  tubing, for the same  OD  tubing...period.
> Same deal  with  copper wire  vs  aluminum wire...for the same gauge.   Dont believe me, try winding an aluminum tubing coil, identical to whats
> in a  hb linear amp, then  compare the difference.  The aluminum  coil will run a helluva lot hotter.
> 
> 

Aluminum resistivity is 2.65, Copper is 1.68
Skin depth at 7MHz for AL is 30.97 micron, for Cu is 24.66 micron

So, resistance of a coil in Al vs Cu is = 2.65/1.68 * 24.66/30.97 = 1.26

Q of a Al coil would be 80% of the Q of a Copper coil.

Assuming the current in the coil is the same, the resistive power 
dissipation in the Aluminum will be 60% higher.

In a RF tank situation where you have high Q (say you're operating Class 
C) that's noticeable - mostly because of the high circulating current.

In a Antenna loading coil or matching network situation, where the Q is 
pretty low (so you don't get much resonant rise) and the coil 
dissipation is 1% of the total system, you're looking at a change from 
1% loss to 1.5%, which is pretty small.

On a vertical, where half the power is probably lost in soil heating..