GPS Antenna for RTL-SDR - Page 1
Forum section: electronics / rf-microwave

author: Axk
author_rank: Regular Contributor
timestamp: March 14, 2020, 04:11:37 pm
content: I'm trying to receive GPS with a cheap active gps ceramic patch antenna like this one:https://www.aliexpress.com/item/4000414502949.htmlI'm using the RTL-SDR blog v3 dongle with its bias-t enabled.Enabling the bias-t does result in the rise of the noise floor as see in SDR#.I'm using GNSS-SDRLIB and I only get very weak reception of 2 satellites max (the antenna is taped to a window pane and shielded with a piece of foil from the inside of the room).Without the foil it doesn't see any GPS satellites.The spectrum in SDR# looks quite "spiky", especially without the foil, so I guess the antenna picks up EMI, probably from the desktop because when I bring the antenna right next to the box the noise floor is rising by about 20 dB and the spikes become more prominent.I've also tried correlating the recorded signal with C/A codes in Octave and I need to correlate over 10 or 20 C/A periods to get more or less prominent peaks.If anyone has any experience with such setup I wonder which antenna should I use with RTL-SDR v3 to get better GPS reception.Or if powering it directly from RTL-SDR is coupling additional noise and I should use a separate battery-powered bias-t.I've already killed the antenna by trying to power it directly from 3 AAA batteries, so I'm looking for a better antenna or other setup changes to get better GPS reception with RTL-SDR.I saw blog posts with people demonstrating good GPS reception with RTL-SDR and GNSS-SDRLIB so I suppose GPS reception is possible with RTL-SDR.

author: vk4ffab
author_rank: Frequent Contributor
timestamp: March 14, 2020, 10:30:24 pm
content: Did you try taking the whole setup outside into the clear and trying it? This is what I would do first. It might just be that the antenna needs a clearer view of the sky.

author: Axk
author_rank: Regular Contributor
timestamp: March 15, 2020, 09:02:15 am
content: I did record outside.I couldn't test with gnss-sdrlib outside because it wont run on the tablet's 32 bit windows.But corellating the recording with c/a codes in Ovtabe does find more satellites, but the signals are still weak.I'm expecting to get a good corellation peak over one c/a period, and I still need 10-20 periods.

author: 9aplus
author_rank: Regular Contributor
timestamp: March 15, 2020, 10:09:10 am
content: Try with one more LNA stage in between. RTL-SDR sticks are not famous to be sensitive enoughover 1 GHz... For example on the same collinear antenna FR24 receiver is getting 50 km more on averagedistance compared with stick without LNA.

author: TheMG
author_rank: Frequent Contributor
timestamp: March 16, 2020, 12:23:06 am
content: Any specific reason you're trying to receive GPS signals with an RTL-SDR?You're always going to get better results with a dedicated GPS receiver chipset. Heck, even the GPS receiver in an average smartphone with its integrated antenna will run circles around an RTL-SDR any day.You can get USB GPS receivers for not much more (or less) than the cost of an RTL-SDR + LNA + antenna.

author: Axk
author_rank: Regular Contributor
timestamp: March 24, 2020, 07:07:29 pm
content: Quote from: TheMG on March 16, 2020, 12:23:06 amI'm learning how GPS works, how the GPS C/A signal is modulated and and tracked in receivers.As a DSP learning exercise.Wouldn't make any sense if I was looking for GPS data in a device, would have just used a module.I looked at the specs of the LNA chips used in the antenna (it has a cascade of 2 AT2659S chips) and the supply voltage range for these is 1.4-3.6V and I don't see any voltage regulators in the circuit.Considering RTL-SDR's bias-T is supplying 5V could my issue be because of the overvoltage?(The specs on Aliexpress say 2.8-5.0V, need to check if they're powering the chips in series)