[TowerTalk] Force 12 loading coils

[Robert Harmon]

Jim,

Sounds like copper tubing (without cool-amp) is the way to go.

I am impressed with the JK coils.  Solid aluminun rod and
welded connectors, very nice !  I assume the solid rod coils are pretty 
rigid and
hold their shape and turn spacing nicely.

thanks,
Bob
K6UJ




On 1/4/16 7:17 AM, jimlux wrote:
> On 1/4/16 6:24 AM, Peter Voelpel wrote:
>> With wider turn spacings capacity between turns is lower and coil Q 
>> higher.
>>
>> Centre loading is more sufficient then base loading on shortened 
>> antennas.
>>
>>
>> Silver plating of coils with cool-amp is for the birds.
>>
>
>
> I'll agree with Peter here.. Skin depth at HF is large enough (about 
> 20 microns, 0.0008" in copper at 10 MHz)  that a thin layer of silver 
> isn't going to make very much difference. Silver is only 5% lower 
> resistivity, and skin depth goes as square root of resistivity, so 
> skin depth is pretty much the same for silver as copper.
>
> Typical silver plating thickness runs from 1-2 micron (typical for 
> terminals and components which you want to solder to) to 40 microns 
> (wearing surface, like switch contacts).
>
> Worse than that, usually, Silver is plated over Nickel over Copper. 
> Nickel is magnetic (mu > 50, as I recall) and fairly resistive (8.67 
> for Ni vs 1.67 for Cu and 1.58 for Silver).  Many a microwave engineer 
> has been surprised by the loss of the plated waveguide being higher 
> than the unplated aluminum. Same for PCBs: the usual gold plating is 
> actually gold over nickel on the copper. Maybe 0.05 dB/inch increased 
> loss at 10 GHz.  (I generally figure FR-4 with 1 oz copper traces is 
> about 1 dB/inch at 10 GHz, almost entirely due to the substrate)
> http://www.taconic-add.com/pdf/technicalarticles--effectsofsurfacefinish.pdf 
> shows 0.8 dB/inch
>
> There are silver plating processes directly onto copper, but they have 
> reliability and durability problems: it's hard to get the silver to 
> stick.  There's also a diffusion effect over the long term, but I 
> suspect that for ham applications, this wouldn't be significant.
>
> I think silver plating is chosen because it's easier to solder to, 
> looks nice, etc.   I'll bet an inexpensive dinner that you couldn't 
> tell the difference in performance in an antenna application without 
> resorting to truly extreme measurement methods.
>
> Jim
> W6RMK
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