GPS wire antena for cat collar

Thread Starter

Kevil

Joined Jun 28, 2020
72
I designed Cat Tracker (GPS/LoRa) based on S76G chip which is working well. The four layers PCB has dimensions just 26x12x1.5 mm. The only problem is that the GPS monopole wire antenna 90 mm doesn't have enough gain and the GPS can't get position. Any idea what may help? I need to stow the antenna inside the collar.

 

Delta Prime

Joined Nov 15, 2019
1,150
I designed Cat Tracker (GPS/LoRa) based on S76G chip which is working well.
If it does not have "enough"gain whatever that means next time you design you will not overlook a very important parameter. Or you could come clean and say hey I have this module I would like to know how it works.thank you in advance
 

Thread Starter

Kevil

Joined Jun 28, 2020
72
I was told that the problem is a missing ground for the wire antenna. In my first PCB design (although the chip was not working because of other PCB design errors) I had additional GND pad i.e. regular wire dipole antenna next to GPS & LoRa signal pads.

 

Delta Prime

Joined Nov 15, 2019
1,150
You must provide any & all pertinent information if you wish to resolve and avoid errors in the future. I personally wish to help you out but I need a lot of more information than you have provided.
Most of my designs begin with a hand drawn schematic and design plan. With these, the circuit is prototyped and tested to verify that the design works correctly. Then, using software, an electronic version of the schematic is created. A netlist file is created from the electronic schematic and used in other software to create the physical layout of the PCB. Next, the components are placed and routed in the physical layout software and Gerber files are created. These Gerber files are used in a prototyping system to mill, drill, and cut the PCB substrate. The components are then placed and soldered to the substrate. Finally, the board is tested to verify that it works as expected.
 

Thread Starter

Kevil

Joined Jun 28, 2020
72
Although the components were soldered by the professional company it looks like that GPS pin of the chip may be not soldered properly. I will let check it by microscope and get some pictures.
 

Thread Starter

Kevil

Joined Jun 28, 2020
72
Half dipole length for 1.575 GHz GPS is 90.4 mm (-5%) and for 868 MHz LORA 82.0 mm (-5%). I am going to buy the NanoVNA to tune antenna later.
 

sagor

Joined Mar 10, 2019
479
Your 1/2 wavelength for 868 is wrong, closer to 173mm (almost twice as long at that of 1.575Ghz)
Lower frequency has a longer wavelength, not shorter....
 

Thread Starter

Kevil

Joined Jun 28, 2020
72
Sorry, instead of half the length, I should have written it is a quarter wavelength.

I have found the problem. The GPS inside the chip has very low sensitivity (-146 dBm for aquisition and -158 dBm for tracking) and requires to use the active GPS antenna with 27-30 dB signal gain. On the development board I didn't get the position with passive 5 cm 2.5 dB antenna.
 

andrewmm

Joined Feb 25, 2011
1,757
@Kevil. Well done for the dogged determination to find the problem,
you used the greatest engineer principles of contrast and compare, and the make a hypophysis using ocams razor as to the most likely reason, you then tested.

Well done also for getting back to us all with your results.
 
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