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What I found + more questions

Discussion in 'General Discussion' started by Seedler, May 29, 2014.

  1. Seedler

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    Hi folks,

    In my quest to find out why I find it hard to get gps lock I found out a few things, but also have more questions.

    I found out that my gps module backup battery was dead so I replaced it with a CR2032, its a non-rechargeable but I'm hoping that wont matter. When I was removing the original battery I found out the module draws 0.004ma from this battery. The original battery didn't have any numbers on it, but from its size I think its a 1Mah battery. This would mean it would last for 10 days. The Cr2032 should last 6 years.

    While I was at it I added a 4mm ceramic patch antenna GP.1575.25.4.A.02 from digi-key.

    After a few test nothing much different was happening except it was locking onto 4 satellites much quicker (I'm guessing that means the battery is working), but it was still hard to get a lock and the satellite number was all over the place as usual.

    So I ripped her down again and added another 4mm antenna, tested, still the same. I was expecting great results from these antennas so I was really disappointed.

    I ripped her down again and that's when I noticed this:


    This small module was not in place. I done a bit of research and found out that the larger black module below it is an LNA and saw filter. This means that we do have active gps so our reception should be great. I found out that the pin this small component connected to is basically the on/off switch for the LNA. I'm not sure if I did this when adding the antenna, or it has always been this way. But I thought that if the LNA has never been on it would explain a few things. Great I thought, I'll just connect this and all will be fine. Not as easy as it looks, this thing is small. Anyhow I appeared to get it in place and went out for a test and still no joy. I don't know if I got it connected correctly or damaged it while soldering.

    Should I definitely notice the difference between the LNA being on and off? Is this little component a resistor? Does it have an input and an output side?

    When I put the multimeter to it it reads at 4.7k. I am reading voltage on the right side of the component so I know I got it soldered to the left pad ok, but I cant tell if I have it soldered to the right pad ok. Does anyone know how to test if there is power going to the LNA on/off pin?

    The voltage at these components reads 3.27v when main battery is connected.

    Hope someone can help with my questions, and sorry for the long post.

    Thanks,

    Damien.
     

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  2. N017RW

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    It does appear and measure like a resistor. 4.7K is a common value.

    If you Google the GPS module for images you'll see photos of your module and the correct orientation of the part on the pads.

    It [resistor] is not polarized so there is no in or out 'per se'.
     
  3. darwin-t

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    What exactly does the backup battery do in this case? "Remember" the last location used to make GPS lock quicker? Anything else?
     
  4. Seedler

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    I believe it stores Real Time Clock and satellite orbit information for quicker locks..

    I thought resistor myself. Any idea how to test if power is getting to LNA?

    Cheers,

    Damien.