PostCard u.fl antenna connector questions

GPS/GNSS
1

Great Product Documentation, but I need some guidance.

The PostCard is so small, it’s natural to start thinking of its use in space-constrained applications.
The snag I’m having is the SMA connector obviously demands that the coax leaves the board in this direction but it also requires a decent amount of space outside the boards footprint before redirecting the antenna cable/coax towards the antenna location.

The Hardware Overview mentions:

While there are two GNSS antenna connectors, only the SMA connector is connected to the LG290P GNSS module by default. If users wish, they can rework the 402 resistor on the antenna trace to utilize the u.fl connector instead.

The Schematic shows:

image
image492×335 22.2 KB

The 3D Model:

image
image544×443 30.2 KB

Questions:

  1. Is the reference to " the 402 resistor" indeed what I’m looking at on the 3D model (the unpopulated pads), and R20 on the schematic ?
  2. If R20 was populated in the future, could anyone use Either antenna connector ?
  3. Given the nature, sensitivity, etc, of an RTK product like this - would the tiny coax used in most u.fl be limiting in this application (in regards to signal strength, noise, etc,) ? IE: should I forget about using u.fl ?

My scanning electron microscope is “in-the-shop”, so I personally wont be reworking that surface mount resistor anyway :wink:

Thanks in Advance,
Ryan

2

Hi Ryan,

0402 is the resistor package size. Correct, ideally you’d rework R19, swinging it round onto the R20 pads. Doing that will leave a teeny tiny RF “stub”, the ~1mm of track going to one end of R19, but it’s the best way to do it without cutting tracks.

If you want to experiment, link the two R20 pads with a blob of solder, and leave R19 alone. This creates an unbalanced Tee, which will degrade your signal. But you probably won’t notice the difference, so long as you use either-or, not both… You can use wick to remove the solder blob afterwards. Make sure the board is off while you do all of this, and take anti-static precautions too.

Short u.FL to SMA pigtails are readily available. 6" of tiny coax will degrade the signal ever so slightly, but you’d struggle to notice the difference. Use regular coax to connect your antenna to the pigtail.

I hope this helps,
Paul

1 Like
3

Paul, thanks for the info. That sounds like something worth trying :slight_smile: