Hello A.N.,
it took me a while to find out what is going wrong here: Your data points do not really fill a plane, but rather lie on a straight line. You can see this with:
Graphics[Point[data[[;; , {1, 2}]]], Frame -> True]
ListContourPlot
cannot work that way.
Instead of working with data you can define a analytical function:
constL = 0.0000346737;
constR = 100000;
f[x_, y_] := (1 - (1/(10^y))*(10^x)^0.7*constL)/(1 + (2.*Pi*(10^y)/10^x*constR))
which can be plotted like:
ContourPlot[f[x, y], {x, -10, 30}, {y, -10, 20}, Mesh -> None,
ContourLabels -> All, ContourShading -> None,
Contours -> Range[.2, 1, .2]]
This gives the result you are expecting!
Henrik
Addendum: I do not want to change your concept. Of course you can work with data values as well:
constL = 0.0000346737;
constR = 100000;
data = Flatten[Table[{x, y, (1 - (1/10^y)*(10^x)^0.7*constL)/(1 + (2*Pi*10^y/10^x*constR))}, {x, -10, 30, .1}, {y, -10, 20, .1}], 1];
ListContourPlot[data, Contours -> Range[.2, 1, .2], ContourLabels -> All, ContourShading -> None]
This also gives the expected result.