I want a way to spoof GPS signals within my own home such that devices e.g. my phones cannot geolocate themselves using GPS, or get a reading with a pre-defined wrong location.
At the same time, I don't want to affect devices outside my home.
It doesn't need to fill my home either, I'd be happy with a PCB that be stuck to the back of my phone or in a backpack that does this for a 30cm radius.
As for jamming it, I think most GPS receivers probably saturate at around -60 dBm in band, so you can probably just strap a noise diode with a suitable filter on the back of your phone or something...
Alternatively, I could just move my fake location a few blocks down the road and it would be enough to satisfy my privacy wishes while not being too much of an outlier.
Still though, I would like to at least /try/ it rather than just sitting here and doing nothing about it.
You might be able to set your bssid to all zeros or something to fight this tracking. Not sure if this would lead to your devices no longer associating though...
Some time back, I was helping prep a uBlox MAX-5Q receiver for a high-altitude balloon flight. At altitude and with no other noise around, we figured we could get away without an amplified antenna, so we had a little passive helix design. But before attaching that, for giggles, I just soldered a piece of plain wire to the module's antenna pad, trimmed to what I eyeballed as probably roughly something approximating a quarter-wavelength at 1.5GHz-ish maybe.
It got a 3D fix within moments. Indoors. On a workbench under a mountain of test equipment. With a ton of RFI around. In an industrial building with 2 layers of roof. With a paperclip for an antenna.
And that was a 5th-generation receiver. We're up to the 9th generation now and they've only continued to improve.
Yes, most cellphone locations are wifi geolocation, because it takes less power. But even if you can render that moot, the GPS signal itself is plenty strong to receive indoors. And modern chipsets are tracking at least 3 and maybe 4 constellations, giving them a lot more satellite options, so there's almost always a good set overhead at favorable angles.
Did your receiver work at high altitudes? I guess ITAR rules have been relaxed so GNSS receivers are allowed on balloons with no problems nowadays.
One of these days I'm gonna sit down with SatGen and figure out how to make a track that rises to high altitude, then simulate it with gps-sdr-sim and do some ITAR testing. I have a HackRF with a stable enough clock, and I have the shielded test enclosures, I just don't have a good way to generate a track that's not at sea level.
As for your results... Those are some pretty fancy receivers, do I know you as a fellow Galmon contributor? There's an F9P on my windowsill as station #41, and I had an M8U on my desk last week. Each has gotten a fix just fine sitting on the desk, by the way.
In your office I suspect the glass has a low-E coating which is metallic, and effectively forms a skin over the whole building. No explanation for the house though; I see moderately slower TTFF times and sometimes poor C/no stats for certain parts of the sky, but otherwise things work just fine in my house. Is there a way to get a background noise level rating out of these receivers?
Yeah, probably my office building has some sort of shielding... I barely even get cell reception in my office, even sitting by the window.
It worked better in my apartment, but I had to basically hang the antennas off my window. I have since moved from that apartment and have not tried in my new place, although I suspect it would be worse since there's another tall building across the street. I did (and still do) live very close to an elevated train line, which noticeably produces tons of noise (as in my TV antenna cuts out...) whenever a train goes by!
But you really don’t want to do this in any way that could possibly leak out. You will make a bunch of connections you never wanted to make.
Or maybe I should just desolder the GPS chip, if I can figure out which one it is.
Tencent does some horrible things with software beyond the laws of China. Apple does too -- that's why I don't use an iPhone as my normal phone. But I have to use an iPhone for certain test apps and I'd like to be able to spoof GPS for Apple and Tencent at the same time.
I'm much more concerned about these companies invading my privacy than the US or China government.
Also, I don't actually have an option if I want to maintain my social life.