I've been really puzzled by seemingly sporadic behavior of my GPS dongle... until today.
I just could not figure out the pattern in which it would sometimes work fine and sometimes get no fix at all.
Most of the time it looked quite funny in fact: during set-up and testing at home everything worked, but once I went on outside to shoot targets, there was no fix.
I even ended up getting an upgraded version of the dongle with a newer chip, just to get to exactly the same erratic pattern.
Now that I have upgraded from Astroberry to manually built indi on a newer OS, I needed to try setting up GPS again.
My Pi is riding piggy-backed on the OTA right on top of the [active] USB hub, into which I plug the devices, including the GPS dongle.
In fact, the full sandwich is 3-layered: USB hub, then the SSD drive, and then the Pi.
I took out the telescope with everything attached to it out to the balcony, attached the cameras just to simulate everything, and had no GPS fix at all for several minutes under clear skies.
I must note here that cgps is actually saying it sees 29 satellites, but using 0 of them, which, according to some sources, could be explained by its inability to actually differentiate the actual signal from the noise.
I read about some USB3 interference with GPS signals. So I re-plugged the GPS dongle into the only vacant USB2 port on the Pi itself. No effect.
Next I took a 2m USB extender to move the GPS farther from the computer itself — no fix in both USB3 and 2 ports.
Disappointed, I moved everything inside the room and was just about to start disconnecting everything... when I noticed that cgps was suddenly showing a 3D fix! (The GPS device on the 2m extender was still out on the balcony)
So I ended up grabbing the telescope bag in my hand and moving it out to the balcony and back into the room, while myself standing in the door and keeping the GPS outside all the time.
The pattern could not be clearer: whenever the computer was outside of the room (out on the balcony), the cgps was showing no fix, but as soon as I would move the Pi across the door into the room, cgps was quickly acquiring the fix!
Now, full disclosure, the whole "package" that I have on my OTA is a bit of a "nest" in the sense that it's quite compact and has quite a bunch of devices all next to each other:
- Power distribution panel that feeds all devices listed below
- Dew heater controller
- USB hub
- Raspberry Pi with its dedicated 12V->5V converter
- SSD
plus a bunch of wires, obviously.
Out of the 4 USB ports on the Pi itself the 2 USB3 ones are taken by the USB hub and the SATA->USB adapter via which the SSD is connected, plus the USB wi-fi adapter plugged into one of the USB2 ports, leaving the other one vacant.
Everything else (2 cameras, mount, focuser and GPS) is plugged into the hub.
I am a bit lost in trying to interpret results of this experiment as I used to assume that overall electrical interference inside my apartment would be stronger than outside.
Would anybody have any idea on what exactly is going on and how to get GPS working when the whole set-up is outside? Maybe wrap some devices in aluminum foil? Get a better USB hub with isolation?
Both the hub and the power distribution panel are pretty cheap off AliExpress, but they have been working for quite a few years already with basically no issues...
Thank you for reading!