fFINAL REPORT Cu COIL vs Al COIL (fwd)

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Date: Mon, 08 Oct 2007 17:18:01 -0700
From: Ed Phillips <evp@xxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: fFINAL REPORT Cu COIL vs Al COIL

    Here is a final report on the experiment I ran to compare aluminum
and copper conductors at RF.  The coils were as close to the same as I
could wind them without going to the trouble of putting them on a form. 
Just air core with masking tape to hold them in shape, hardly an optimum
design but good enough for these measurements.  Table looks OK here and
hope it comes through.  If not will resend IF anyone is interested.  I've
had my fun so the effort is not in vain.

                            Al                           Cu
            _______________     ______________     
   f         Q        C        Leff     Q        C        Leff    Q
(Cu/Al)
5000    565    103.5    9.78    655    102.2    9.91    1.16
4500    547    129       9.69    625    129       9.70    1.14
4000    515    164       9.65    600    163       9.71    1.17
3500    505    214       9.66    565    211       9.80    1.12
3000    479    293.5    9.59    535    291.5    9.66    1.12
2500    438    428       9.47    495    423.5    9.57    1.13
2400    425    463       9.50    490    460       9.56    1.16
      0      0                                0

Frequencies in kHz, capacitance in uufd         
                               
Data            Al           Cu                       
WIRE        0.125"    #12               
Rdc mW    12.3        17.3               

    Bottom line is that the Q of the copper coil was close to 15% higher
than that of the aluminum coil wound with a larger conductor.  The
inductance of the copper coil was about 1%  higher so, assuming the AC
resistance of the wire was independent of turn spacing, for the same
inductance its Q would be 1% lower and the ratio of Q's would be about
14%. 

    Here's some tortured reasoning saying this difference is reasonable
and about what be expected.  Per simple theory the ratio of the AC
resistance of wires of the same size should vary inversely as the square
root of the resistivities and should scale with wire size as the inverse
of the diameter.  Based on this I think it's safe to say that,
independent of wire diameter, the ratio of AC resistance to DC resistance
should scale inversely as the square root of the DC resistance.  This is
certainly comparable to the observed 14% and probably not coincidental.

    I should mention that these data were measured with a 50 year old [at
least] Boonton 160A Q meter with "swap meet" calibration.  All of the Q's
were high enough that I had to use the X2.5 setting on the drive meter
and it was mighty difficult to make sure the adjustment was the same each
time.

Ed