On 10 May 2006 10:34:13 -0700, "K7ITM" wrote:

LMR400 outer conductor should be a bit less than 10 milliohms per foot
at 4MHz.

So... close to 0.140 ohms loss restance for the loop conductor, and if
the loop is resonated by the o/c stub which presents an impedance of
around 0.14+j116, and taking Richard's estimate of Rr at 0.002, the
the efficiency of the main loop (ignoring coupling loop / circuits) is
about 0.002/(0.14+0.14+0.002), less than 1%, or about 21dB of loss.

It seems that the convenience of the TL loop / capacitor comes at a
significance expense.

Owen


Rule of thumb: for copper, assuming thickness at least a couple of
skin depths, RF resistance in ohms per thousand feet is about
sqrt(freq(MHz))/(diameter(inches)). Aluminum will run 25% more or so.
I've assumed the aluminum foil shield of the LMR400 is at least 3 mils
thick, and I've neglected the overbraid.

Cheers,
Tom
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