SparkFun Forums

[Damonwill]

All

I've searched many forums and haven't been able to get a solid answer on this. Using PCB123 to create prototype boards. Using a A2200-A (digikey 927-A2200-A) GPS module and a passive GPS antenna with a pin. My questions are, how do I design the 50 ohm stripline to maximize sensitivity if I have a 2cm flying lead that goes to the GPS antenna pin? Does the flying lead affect it? do I need a coax to have a shield to ground for the flying lead? and most importantly, what can I use to design the stripline? Never did it before and don't have the best understanding of why its important. Other than it is important...

Thanks!!

[dlotton]

Here's a link to some stripline/microstrip calculators. There are probably hundreds of them online...

http://www.ekswai.com/en_stripline.htm

The calculators help you determine critical dimensions to achieve the target impedance for the stripline (or microstrip). I think you may find that if you're using PCB123, you may not have sufficient control of some of the dimensions (e.g. dielectric thickness, layer stackup) to achieve your target impedance, especially for a stripline (as opposed to a microstrip). For a stripline you have to control dielectric thikness on both sides of the signal trace.

Stripline = signal trace is sandwiched between two reference planes
Microstrip = signal trace is referenced to a single reference plane

Can you not connect the flying lead from the GPS directly to the antenna?

Impedance mismatch between the cable and stripline/microstrip will affect sensitivity, as will overall length of the signal path. The safer bet would be using a cable, if you can do that.

[Damonwill]

Hmm, actually yes. I could go directly from the gps module to the antenna using a coax. any design tips for that configuration? It will have to be a thin coax to fit inside the enclosure....

[dlotton]

Hmm, actually yes. I could go directly from the gps module to the antenna using a coax. any design tips for that configuration? It will have to be a thin coax to fit inside the enclosure....

I don't really have any specific tips. I'd just try to find someplace online that has what you need or can build it for you. Connectorizing coax can be challenging if you don't have the right tools and/or knowledge. There are some mini-coax selections that get pretty small that should address your size concerns.

L-Com (link below) has some cable assemblies. You'll need to know what connectors you require on each end and make sure the mini-coax is compatible with GPS band.

http://www.l-com.com/coaxial-cable-assemblies

[dlotton]

L-Com also has a decent tutorial page...

http://www.l-com.com/content/Coaxial-Ca ... orial.html