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GPS problem solved (Finally)

Discussion in 'General Discussion' started by Seedler, Jun 26, 2014.

  1. Seedler

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    Hi folks,

    Just a small update on my gps problems. They're solved, woo hoo.

    A small recap. Ever since I bought my phantom I have found I hard to get a full lock, usually only getting 6 satellites, and loosing them in flight. So I started looking into my gps module.

    These are the steps of what I did:
    1. Found the small battery in module was dead so replaced it. Made no difference to number of satellites.
    2. Replaced antenna with high gain antenna. Make no difference.
    3. Found that a small resistor that sends power to lna on/off pin was not in place. Soldered it in. Again made no difference.
    4. Tried another high gain antenna. Still same amount of satellites.
    5. Decided to put the original antenna and battery back just in case.

    After the final step I didn't get any satellites at all. Accepted the fact that I had damaged something and was about to buy a new module.

    But decided I'd bypass the lna and solder a wire from the antenna pin to the Ublox module just to see what would happen:

    As you can see the soldering isn't very good but I wasn't expecting anything to change. Tested it outside and to my surprise it locked on in less than a minute and got 12 satellites. Amazing I've never got that many. I've had no problems with gps since. I can even see satellites in my house now, and I live in an old stone house with 3 foot stone walls.

    Don't know what's happening here. If I'm even benefiting from the lna at all now, but I don't care, it works :)

    I'm over the moon now, but I'm also annoyed. This has obviously been a problem with my phantom from I bought it. For the price of these things you would think they were well tested before they were shipped out.

    Cheers for listening. Maybe it can help someone else with same problem.

    Damien.
     

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  2. dragonash

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    wow, congrats.

    Good thing you knew something about the circuitry! What is the INA anyway?
     
  3. ianwood

    ianwood Taco Wrangler
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    So, if understand that correctly, you had a bad trace/contact between uBlox module and the LNA or LNA to the antenna? Or are you saying the LNA was bad and you bypassed it? Have you tested it mounted in place on the Phantom now that you bypassed the LNA? Curious what the absence of the LNA will do.
     
  4. Seedler

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    I think I damaged the trace after all my workings, that's why I ended up with no satellites. I'm guessing the original problem was coming from the lna. Yes I've tested it with the wire in place and I now see all satellites. Suppose its not really a bypass, its in parallel with lna.

    Damien.
     
  5. Seedler

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    From what I've read the lna is a (low noise amplifier and saw filter) Think it boosts the signal and cleans up any interference

    Damien.
     
  6. N017RW

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    I too hope you are successful but the engineering is not on your side.

    Bypassing the LNA reduces sensitivity and immunity to near by frequencies that could cause 'jamming'.
    (Seems like you are aware of that).

    The other concern is the impedance of the feed line. It should be maintained at 50 ohms or [further] signal degradation may occur by de-tuning the antenna.

    I applaud the spirit and trail-blazer attitude!
     
  7. sar104

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    Nice work - I would not have been that persistent. And you have satellites in your house? Just small ones I assume.
     
  8. Helveticus

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    :lol: :lol: :lol: Had to spit out a mouthful of coke through the window or it would have ended up on my keyboard/screen !
     
  9. Seedler

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    Yes only mini ones :)
     
  10. Seedler

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    I believe it was the lna that was at fault from the word go. I have an app that tells me how many satellites are visible at different times of the day. I now see them all. So whether the lna is working or not, you cant get much better than that :)

    Damien.
     
  11. ElGuano

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    Glad you got it working.

    Interestingly, the Phantom module is the only DJI GPS part I'm aware of that actually has the secondary SAW filter installed. The puck GPS's don't have it. I've also heard of people modding to ADD the saw filter to increase GPS precision and reliability, this is the first I've heard of a move to bypass it.
     
  12. Seedler

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    Just another update folks. Think the module is totally fried now. Everything was working well until one day I was getting no satellites. I checked my other devices and they were getting zero satellites as well, so I thought it was interference of some sort. After a bit of testing I realised that the Phantom was jamming the gps of my satnav. Strange.

    Everything was surrounded with glue and when I removed it the wire soldered to the ublox came off, so I don't know if it had came loose or I pulled it off. Re-soldered it back on and tried again. worked but only the way it was working out of the box. Could only lock onto 6 satellites and took ages to lock on. Thought it was a bad solder so tried re-soldering again. Now I'm just getting an orange light on the Phantom and the assistant software says I have no gps module, and I'm not getting any compass data. must have fried something this time.

    I was so over the moon about the huge number of satellites I was getting the first time I added the wire. That's the universe for ya :)

    Hope a new module will bring me back to those numbers.

    It was a hard battle that I thought I'd won, but in the end it beat me :(

    Damien
     
  13. The Editor

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    Were you using an ESD safe soldering iron/station?

    If not, static may well have destroyed some components without you even knowing. :cry:
     
  14. OI Photography

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    Right there with you Damien, I lost that same battle a few weeks ago. I was trying to replace the antenna on my GPS module and when I removed it the same center pin came off, and took with it most if not all of the trace on the board that goes to the hole/post. After spending several hours and half a spool of wasted solder trying to fix it I finally gave in and bought a new board. Still bugs me though.
     
  15. Seedler

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    Probably not. It was just a cheap 30w iron. Should probably invest in some decent tools.

    Ah well, live and learn :)

    Damien
     
  16. Seedler

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    I know, I would rather work something out myself too, or at least know how it broke.

    Damien.