Help Debugging Fisher Transform Code (Ehlers)

The attached file is a chart showing a test on the S&P 500 for the past 10 years.

This looks obviously wrong and I may be having problems with how I scale/normalize the data before passing it to the Fisher Transform function.

NOTE: I am not using smoothing via Moving Averages or Exp. Moving Averages as I am trying to simplify my code to identify the main error. It may have to do with using a global min and global max for data scaling.

Pseudo Code:

Code:

# normalization / scaling to keep data within (-1, 1)
gMin = min(ts)
gMax = max(ts)
gRng = gMax-gMin
gMid = (gMin + gMax)/2.0

for i in range(0, ts.size-1):           
	t = 2 * (ts[i]-gMid)/gRng
	
	if t < -.9999:
		t = -.9999
	elif t > .9999:
		t = .9999
	
	#           t -= .5
	ndata.append(t)

#fisher transform being applied below

ndata = .5 * ln( (1+ndata)/(1-ndata) )