subroutine qlfnh (rz,fnb,hb,fnm,hm,h,a,b,fn)
c	s/r to find the parameters A and B for a quasi-linear layer
c	through the two points (fnb,hb) and (fnm,hm), and the plasma
c	frequency, fn, at a specified height,h
c
c	written by leo mcnamara 8-sep-88
c-----	last modified 9-sep-88
c
c	the layer is fn**2 = a * (r/rb)**2 - b
	top = fnm*fnm - fnb*fnb
	bot = ((rz + hm) / (rz + hb)) **2 - 1.
	a = top / bot
	b = a - fnb * fnb
c
	r = rz + h
	rb = rz + hb
	fn2 = a * (r / rb )**2 - b
	fn = sqrt (fn2)
c
	return
	end