Hi,
After some hours of trying to get a fix with the GNSS receiver on the VU GPSDR board I decided to connect an active GNSS antenna. I used a small cable (pigtail) with a connector suitable for the GPSDR antenna connector a SMA female connector. With this set-up even inside the house I got a fix within a few minutes. This is conform my experience with GNSS u-blox modules connected via a serial to USB interface and using U-center. To investigate further I connected the GPSDR patch antenna (13x13mm) to one of my U-blox M8N modules. It took a long time to get a fix with the GPSDR patch antenna, less satellites and the deviations were much larger than with the patch antenna (20x20) delivered with the module.
For me the patch antenna seems to be inadequate and I plan to make a 3D printed back plate with the possibilitie to attach the SMA pigtail permanently to the GPSDR unit.
By the way I also went also through all the power problems with the Vivid Unit combined with the GPSDR. Facing USB-C cables that don't work and USB chargers that don't work even when specified for 5V, 3 Amp. I got it working with a Samsung Super fast charger with its original USB-C to USB-C cable and with an Anker powerbank with an USB-C to USB-A cable connected to Vivid Unit extender board.
The 18x18mm GPS antenna on VU GPSDR is already an active one, and it has an LNA with about 30dB gain built-in. Its performance may get limited by the way it is placed.
We never have problem to get a GPS fix outdoor, sometimes we even get a fix inside our office (the emerald LED lights up).
We did tested some bigger active antennas with iPEX-to-SMA adapter, and some of them did get better performance. Probably due to:
- bigger antenna size, and
- the flexibility to adjust angle during usage
@admin It is probably true that you get a fix outside with that small patch antenna. But I see a significant difference between that antenna and the patch antennas with a larger dimension when I connect it to a GNSS-module with an original U-Blox Neo M8N module while observing the performance with Ublox's U-center. The C/N0 is lower, the amount of satellites is lower, the position deviations are larger (50 m against 5 m). To really make use of the frequency output I assume that one needs to have a stable fix providing the 1 second PPS sync pulse. Maybe the active part of my GPSDR patch antenna LNA gain is lower than its specification or it is faulty. The actual position I used for both patch antennas was exactly the same.
Can you tell me the configuration of the U-blox Neo M8N on the GPSDR? As it is using the I2C communication I don't have a means to query the module with the UBXTool that communicates over serial or USB-to-serial COM ports. I guess I could take the GPSDR out of the extender board and hook up a serial to USB interface to the serial header near the U-Blox Neo M8N module marked as RXD, GND and TXD and connect the 3.3 V near IC31.
The TXD and RXD of M8N module has already been brok out to the unpopulated header P1 (on the right of the M8N), and you may try your connection from there first.
The STM8 microcontroller also queries the module in the background, and I am not sure if that will affect the communication with your UBXTool.
I am not sure what kind of configuration are you looking for? If you wonder how GPSDR++ initialises the M8N module, it is all in the gps.c file: https://github.com/uugear/GPSDRPP/blob/main/core/src/gps.cpp