Lpc2000

--- In lpc2000@yahoogroups.com, "Leon Heller" <leon.heller@...> wrote:
>
> ----- Original Message ----- 
> From: "Guillermo Prandi" <yahoo.messenger@...>
> To: <lpc2000@yahoogroups.com>
> Sent: Wednesday, May 03, 2006 12:50 PM
> Subject: [lpc2000] OFFTOPIC: PCB impedance calculation without GND 
plane
> 
> 
> > Hi. Sorry for the offtopic, guys. If anybody can point me out 
some good
> > forum/group to post this question, I'll be glad.
> >
> > I need to calculate trace witdh and cleareance to achive an 
impedance
> > of nearly 50 ohm for an RF trace surrounded by a GND polygon. My 
board
> > is SINGLE layered, so I have no power or GND planes. There's 
plenty of
> > online calculators for this *if* I have a GND plane, but I 
couldn't
> > find any for surface impedance calculation (i.e., between 
tracks). Any
> > hints?
> 
> You will find it impossible to get a 50 ohm impedance the way you 
describe. 
> Why not just put some copper pour on the other side of the track, 
making it 
> a microstrip section. A track width of 0.1" will give you about 50 
ohms with 
> FR4 material. If you are stuck with a single-sided board you could 
glue a 
> piece of copper foil to the other side of the board or use some 50 
ohm coax 
> cable. If the connection is short and the frequency not all that 
high, I 
> wouldn't bother with impedance matching anyway.
> 
> Leon
> --
> Leon Heller, G1HSM
> leon.heller@...
> http://www.geocities.com/leon_heller
> 
> Leon 
> 
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>

Thanks, Leon. I'll keep in mind your suggestions if I bump into this 
problem again, but you're right, a second layer is way easier. The 
line is relatively short (1 inch), but frequency is GSM (1.8/1.9 
GHz), so I want to be careful to keep signal integrity in good shape 
as much as I can within reason.

Guille