Lpc2000

----- 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 

---
[This E-mail has been scanned for viruses but it is your responsibility 
to maintain up to date anti virus software on the device that you are
currently using to read this email. ]