It's so weird. This GPS antenna seems to only work with line of sight.
2mm PETG plastic in front of it and it stops working.
Is there a better antenna?
Those modules are dirt cheap for a reason. They are poor quality imitations of the genuine item and don't work well.
That looks like a circa 12mm ceramic patch antenna.
The 25mm ones would likley work a lot better.
Maybe you can search for ceramic patch antennas in amazon and buy a branded ( I mean well-reviewed) one. Anyways, I have a question, How can these antennas have direct contact with satellites millions of km away? Do GPS satellites transmit such strong signals?
Because they dont.
GPS satellites have an orbit of circa 20km.
What you are calling the "antenna" is actually a very low-noise, sensitive receiver in a metal shielded enclosure under the actual patch antenna. The antenna and the metal box make a complete enclosure to keep any noise out of the receiver.
We used to make the circuit boards for a marine electronics company that used the patch antenna/ receiver on their board. One time one of the "antennas" came apart in the reflow oven and we could see all the stuff under the antenna. Pretty impressive.
The patch antennas can be either passive or active. If a GPS module incorporates a passive patch antenna then there are a few additional components on the module's board. I was also curious to see what was inside and could not find an online teardown so I ripped one apart, an active one which came with a defective module. There was not much in it but I seem to remember one weird 4 pin RF transistor. I've still got it somewhere and can produce a picture if anyone is interested.
That would put them in the Earth's atmosphere!
They orbit at about 20000km Global Positioning System - Wikipedia
Fair point, I did mean 20,000km.
I should have realised, my own satellite orbited at 700km.
Thanks for explaining, at first I thought GPS satellites are in the Geo-stationary orbit...
That has a height of 42,164 km.
How would that work? They would only be above the equator, so would provide very poor coverage at the poles. No, they are lower and in various orbits to cover the planet.
And they are in constantly changing orbits because the earth is NOT a sphere and the mass/gravity changes from place to place on the earth. There are 5 ground stations in the US that apply adjustments to each satellite's data based on where the device is in it's orbit. There are other stations scattered around the earth that do the same thing. But none in Russia. A very complex operation, indeed!
Here's two pics of what's under the can of an active patch antenna/aerial.
Second pic shows the soldered connection of the coaxial cable. Very weak physical connection. Easi;ly broken if the antenna catches on something if it is left dangling from the GPS board. Also breaks from fatigue if subject to repeated bending. It pays to secure the antenna to the GPS board as soon as you receive it.
Was the plastic touching the patch antenna? That could detune it a small amount perhaps. With all antennas you should have empty space in the immediate vicinity where the em-fields exist (the near-field region). The near-field area is where the magic happens and cluttering it can change the antenna's response markedly.
Patch antennas can be quite complex internally providing multi-mode operation for instance, they are not necessarily just a bit of metal on top of a ceramic block.
Many people come to the forum with the problem that their newly purchased GPS module doesn't get a fix no matter how long they wait or where they set it up. They often condemn the GPS module as a dud and either buy a new one or give up altogether.
I have a notion -- can't prove it -- that the antenna side of the GPS/antenna system is more prone to problems than the GPS module. I think it's more vulnerable to electrical or physical damage, but it's difficult to test its functionality.
Anyone else have thoughts on this?
I am sure there is a big element of truth in that, I too have seen faulty antenans on GPSs. I tend to bin them even though I could maybe fix them.
But those small 5mm x 15mm ceramic GPS atennas that some modules come with are just useless anyway, only really suitable for perfect conditions.
The GPS itself will need to be assembled by relativly sophisticated automatic assemble equipment, so if you want to cut costs its the addition of wires for the anternna etc where shortcuts might be made.
Do you have a way to test an antenna? I can only test by swapping it out with one that does perform.
No, I normally just look at the signals in UCenter.