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Fake multichannel #697
Fake multichannel #697
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Help me understand what this PR does, since the code change is trivial. On line 138 the number of channels from the signal source are extracted (in your examples, this value is 3). Then the three signal conditioners are created. Then, starting at line 933, each channel of the output is connected to a corresponding signal conditioner. As I work through this, what I'm guessing is that the signal source doesn't actually support multiple channels; and you are emulating the multi-channel capability by connecting different processing chains to the same source output. While this is a nice use of the underlying GNU Radio infrastructure, I'm less comfortable with your (under-documented) approach for GNSS-SDR. Personally, I've butted up against the expressive limitations of the config file, and would like for more flexibility, but I'm not convinced (yet) that this is a good change to the baseline. The whole wiring of the the flowgraph is brittle and inflexible, beyond the pre-defined flexibility in this file. I'm wondering if embracing GNU Radio more closely (maybe even a GRC file) is a better solution to this issue? |
This PR makes it possible to receive multiple constellations at different frequencies using one single channel device. This is achieved by connecting several signal conditioners to the same signal source/channel and setting different IF offsets. |
What is your system configuration? Because I couldn't keep up with the 56MHz stream. My host configuration is, OS: Ubuntu 20.04.5 LTS x86_64 I followed the guidline in -> However, overflow is still occuring. I am not sure volk is working properly. Although, I run |
OS: Ubuntu 18.04.6 LTS x86_64 You may have to apply this patch: vladisslav2011/gr-osmosdr@1888972 You may try to reduce the sampling rate to 48MHz. It should be enough to get both BeiDou and Glonass. |
Thanks for your reply, @vladisslav2011 I will try that ->
I've tried the HackRF configuration and only keep up with 20MHz bw and 2 MHz internal_fs_sps. Also, I will try to run default configuration with more powerfull host which has 20 threads. |
Hi I am trying to use the multichannel gnss receiver with hack rf... when I use the code, it says segmentation fault.. Can you help? |
Signed-off-by: Vladislav P <vladisslav2011@gmail.com>
@aniljangral
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I've rebased this PR on top of current 'next' branch (4836785) and corrected config files placement. |
@carlesfernandez what are your thoughts? This is a trivial change that doesn't seem to do harm, and has been around for a while. |
Thank you for your prompt reply! I am not very good at computers.. Please bear with me!! |
@aniljangral
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@aniljangral |
Hi Thanks! |
Hmmm... "7 overflows occurred" means that your machine is not powerful enough to process full bandwidth or buffers are too small. b205 will not work with this antenna ("GPS Antenna 1575.42MHz"). It needs an external bias tee and 3.3V power supply. |
Signed-off-by: Vladislav P <vladisslav2011@gmail.com>
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Adding more RAM will not help. Try increasing |
Okay. |
There is no need to install patched gr_osmosdr anywhere.
There is no need to install the development version of GNSS-SDR as well. It can be easily run from it's build directory too. |
That's not a bias tee. That's an amplifier... Rebuild gr-uhd or uninstall UHD 4.6 and install UHD 3.15 and matching firmware and FPGA images. |
See, as to best of my understanding, Bias Tee is required to power the LNA present inside the active antenna(antenna + LNA).. so, when i use an external LNA with the normal antenna and power the LNA with an external DC source, it essentially makes an active antenna. Hence, it obviates the requirement of a bias tee.. correct me if I am wrong.. |
Your antenna is active, so it has an LNA inside. This LNA, when not powered, will add ~20...30db insertion loss, so the antenna will not work even with an external LNA. You may disassemble the antenna, remove the internal LNA and matching network and use an external LNA, but the external LNA should be put as close to the antenna as possible especially when the cable is not good at 1+GHz like this long thin RG174, that is usually used with these antennas. |
Not sure if this is the best solution (I think it is not), but let's accept this PR since it seems harmless. |
Very well explained. Thanks then I will have to purchase a bias tee and may take a weeks time at least to be delivered. |
Since the fake_multichannel branch has been merged with next branch, do I need to build the next branch again?? |
Yes. |
Make it possible to receive multiple constellations using single channel wideband device (HackRF/LimeSDR/USRP).
Demonstration: https://www.youtube.com/watch?v=ZQs2sFchJ6w https://www.youtube.com/watch?v=HnZkKj9a-QM