SparkFun Forums

[Superluminal]

Hi all,

Can anyone advise me on the following...

I'm planning to have a play with a Fastrax IT520 GPS module. I need some advice on how to form the PCB trace that connects an SMA RF connector to the antenna pin on the IT520. I know that the trace width needs to be about 0.12" in order to achieve the required 50 Ohms impedance (this based on a 1.6mm thick FR4 PCB).

It turns out that the pad/pin on the IT520 is well under this width, so my question is how do I best reduce the trace width in order to match it up with the antenna pad?

I've had a look at a couple of actual designs. Some don't appear to make any effort to use a suitable PCB trace, others just use the widest trace they can get away with, and I've also seen some designs where the trace "curves in" to match the pad width.

I'd like to try and get this right! Any suggestions or advice would be most welcome...

Max

[Superluminal]

Hi all,

Whilst waiting for my new user moderation to go through I've had a bit of time to research further into my question.

I came across this application note at,

http://www.analoghome.com/news/2011_8_29.html

It's very useful and describes pretty much what I need to do. I've gone for a CPWG solution, and I also used the following trace width calculator at,

http://chemandy.com/calculators/coplana ... ulator.htm

I've also attached an image of the layout (generated in Eagle) in case anyone is interested. The trace in question is the one in the top left connected to pin 1 on the GPS module.

As before any comments or suggestions are most welcome!

Max

[leon_heller]

Over such a short distance the impedance of the track doesn't really matter.

[Superluminal]

Thanks Leon!

I did wonder how critical this would be over such short distances...

I'll probably stick with what I've got and if nothing else I've learnt some new stuff, which is always good!

Max