Addressing skin depth:
For copper:
Conductivity:? σ = 6.30 E +7 S/m
Resistivity:? 1/σ = 1.60 E -8 Ωm
Skin Depth: 2.47 E-5 m
Frequency of following analysis:? 7.000 MHz
For the above, refer to:?
? ??????????????????????? and
?
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From the same reference the resistance due to skin depth can be calculated:?
? ? ?
For my 36-inch diameter loop made of 0.5-in copper tubing (and converting everything to the MKS system) the resistance due only to skin depth comes out to be:
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? 0.0952 ohms
At 1 MHz, this will be "roughy" 0.1X of that value and at 100 MHz, this will be "roughly" 10X of that value.?? These are only roughly.? But it does indicate some frequency dependance.
However, in all cases from 1 MHz through 100 MHz, the added resistance is considerably greater than the DC or radiation resistance.? So, I'd conclude current in the loop should vary with frequency as a result of skin depth.? In addition, the variation between "DC" and 30 MHz should be only a factor of "roughly" 10.?
Interestingly this goes against the EZNEC analysis presented earlier.? It showed current pretty much constant even up to resonance.?
Guess someone needs to actually measure current as a function of frequency with a constant RF input level.??
I can short my 36-inch tuned loop to do that.? Anyone else want to contribute in this measurement????
Dave - W?LEV
