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..
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