Hi All,
Late yesterday I re-installed the 200ft of 1/2" copper pipe in my std
50'/50' loop location. The pipe had been laying on the ground in the back
woods for about 6 weeks while experiments with other loop conductors were
going on. During this time I had begun doubting the accuracy of my
measurements with this conductor some time ago, that, according to my notes,
had an Rac of less than 0.5ohm.
Just before removing the RG-8 conductor I measured the Rac at 0.82 ohms. It
had rained 2 days before so the ground was still a bit damp, so this reading
was probably high by about 0.05 ohms compared to a 'dry' condition. Another
factor is that I am using the transmitter INPUT power of 1w to make the Rac
calculation and this fails to account for the loss in transistors, resonant
capacitors, and output transformer. I will re-calculate this later based on
the actual output power and this will reduce all Rac measurements by ~7%.
The installation of the pipe was actually easier than anticipated. I used
the RG-8 to pull a #8 wire over the top and then the #8 to pull over the
pipe (which is quite compliant). The pipe is composed of twenty 10ft
sections all soldered together and the total weight is 40lbs. This is
standard thinwall house plumbing pipe at $3.15 per section at Home Depot.
The OD is .63" and the wall thickness is 0.03. No support ropes are needed
since the trees totally support the pipe.
I was surprised, and relieved to find the Rac measured 0.49 ohm! After an
all night rain I see the input current is down by about 8% and I will
recalculate the Rac tonight. BTW this is ~185kHz.
I have calculated the Rac for the following conductors using the .0062" skin
depth, using 0.2 ohms for soil loss, and nothing included for tree loss:
(and yes, Mal, the actual measurements Do check out pretty close :-)
1) #12 1.31ohms 2) #8 1.13 ohms 3) RG-8 0.82 ohms
4) 1/2" Cu pipe 0.49 ohms
Next - on to multiple Litz conductors!
Bill A
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