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GPS performance

elafargueelafargue
in KiwiSDR Discussion
Hi,

    Just started to use KiwiSDR, pretty awesome system! I was wondering how sensitive the GPS is on this design? In my experience so far, with the active antenna shipped by Seeed, it is not super sensitive compared to integrated modules, but at the same time, we are talking about a GPS for a static location where the actual fix is less important than the clock & frequency calibration :)

    One thing I noticed, is that the patch antenna that is in the Seeed kit definitely benefits from being placed on a ground plane - sticking it to a large metal plate using its magnet makes a night and day difference!

Keep up the good work.

Comments

  • jksjks
    In my experience the GPS sensitivity seems to be a little marginal. But it is very difficult to quantify. I don't have the specialized test equipment to make sensitivity comparisons.

    The GPS front-end chip used by the Kiwi (Skyworks SE4150L) is a standard part used by millions of GPS receivers worldwide. But there are so many things that can contribute to reduced sensitivity. But for example I have an ancient Garmin Nuvi that uses the same chip (I think) and it can work indoors just fine using an internal patch antenna not dissimilar to the Kiwi. Whereas the Kiwi's active antenna must definitely be outside with a clear view of the sky and positioned horizontally ("base down") as you note. Now does the Garmin have a better RF amplification chain? Better firmware/software to pull signals out of the noise? Who knows..

    To place the antenna where needed during development I had to extend the 3m coax of the active antenna by splicing in an additional length of RG174 and crimping on my own RP-SMA connector. I'm sure the impedance bump and additional loss by doing this was awful. The sensitivity was terrible. But later when I moved locations and was able to use a stock antenna without the spice I noticed an improvement in sensitivity by a factor of two! It was amazing. So that tells me that the SNR of the receiver is not so good and every little thing that can be done will result in an improvement.



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