[NLRS] Help with math

[Scott]

I'm having some trouble with my math (I am NOT a math major!)...

I am trying to find a microstrip width for DEMI circuit board (they call 
it Duroid 5880 equivalent).

If so, it should have a dielectric constant (Er) of about 2.20.

Looking in my (VERY BRITISH) VHF/UHF Manual, here is the formula for 
width of a microstripline...

Log(subscript 10)W= 0.8736 + log(subscript10)t -0.004992 x Z X (Sqroot 
Er) + 1.14

W=width (mm)
t= thickness (mm)
Z=Impedance

So Er=2.20
Z=50 Ohm
t=0.787 mm (0.031")

What is W (in mm)??

Or, has anyone built 50 Ohm line on DEMI 0.031" circuit board and if so, 
how wide were the strips????

-- 
Scott N0EDV
http://corbenflyer.tripod.com/
Building RV-4
Gotta Fly or Gonna Die