Introduction: SIM5320E Shield- GPS Antenna Fix

I bought 3 of these 3G GPS combo shields for making car trackers but that is another story (Future Instructable).

When testing these I found they were not getting a GPS lock at all. They did find a few satellites after an hour. Not Happy Jan.

After some investigation and searching the datasheets I found that the active GPS antenna circuit on the top right had a capacitor at R1 where there probably should be an inductor. I luckily had some parts given to me by a friend who bought up some junk at an auction and viola, there was the exact part I needed.

After replacing the capacitor with a 30nH 0603 surface mount inductor, the GPS acquired a fix in less than 30 seconds, cold start. I call that a win.

What follows is what I wanted to know a few days ago.

Step 1: Locate the R1 Component

Firstly, to check my theory that the bias voltage isnt supplied to the GPS connector, I powered the shield and measured the voltage on either side of R1. 2.7V on the right side and 0V on the antenna side. So no bias voltage to the active GPS antenna.

I unsoldered the capacitor ar R1 right beside the GPS connector.

A fine tip and desoldering wick, heat one side and wick up any solder.

Rinse and repeat for the other side.

Then swap the tip back and forth and apply a little up force to the capacitor. Careful not to lift the pads under the cap.

Once the capacitor is off, a little heat and wick to smooth the pads.

Step 2: Solder in the Inductor

Thanks to Adafruit, I had a look at their design to see what might work. 30nH seems to be about right and that is the one I have in the bucket of spares so that will be the one to use...

RS has this part that I was going to buy if I didn't have anything to use.

RS 30nH wire wound surface mount inductor

I like to use a pair of reverse tweezers to hold the part in position as I solder both sides of it.

Step 3: Happiness

Now when I test the shield, the time to get a GPS fix, the TTFF is less than the time for the ESP8266 micro processor to get connected to my wifi and power up the SIM5320E and check it has a 3G connection. I guess less than 30s from cold start.

Sweet

Comments

author
mic-j (author)2017-08-20

Fantastic work! I bought two of these for the same reason and wondered why it would refuse to get a fix. Inductors are in the mail.

author
WhereisWally (author)mic-j2017-08-21

Ii have 3 car trackers that have been working for years on Vodafone GSM which I just saw will stop in September 2017. Mad scramble to make new PCB and rewrite code this time I am using ESP8266 and Arduino core.

author
mic-j (author)WhereisWally2017-08-24

Yep same reason with Optus. I'm using a Pi Zero W as I'm aiming for more functions than the TK103 it replaced.

author
Swansong (author)2017-08-15

That's a neat fix :)

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