TDOA application


#64

Could you paste a print screen of Device Info window from LimeSuiteGUI (Modules -> Device Info and then press GET INFO button).


#65

Hi Zack,

Here’s the screenshot.


#66

Hi @shao,

Just for my clarification. You are using LimeSDR-QPCIe board, right?


#67

yes


#68

OK, thanks @shao. Now we are implementing phase check software to check phase jumps between channels from different LMS7 chips using LimeSDR-QPCIe board. Will update later with results.


#69

Hi @shao,

Could you make one experiment. Feed all 4 RX channels from one signal generator via RF signal spliter and check the phase with your software. Let me know about results.


#70

@Zack
Excuse my ignorance but do you expect that upgraded TDOA functions
can be used on two LimeSDR USB units on the same clock source?
Regards
Djani


#71

Ok. I will buy the RF signal splitter. If I use a LimeSDR-Mini as my signal generator, is it safe to directly connect it to the receiving port of the qpcie board? Do I need to use a 5dB or 10dB attenuator on the tx port of LimeSDR-Mini to avoid damaging the receiving ports of the qpcie board?


#72

Hi Shao,
You can safely use LimeSDR-Mini (or any otyer similar board/device, even signal generator) to generate test signal for DOA application. Just to fnd why the phase is jumping so randomly. Not to mention. Do not drive RX inputs with 30dBm :slight_smile: Power splitter can even be made quickly (voltage divideer 150 Ohm in series + 50 Ohm to the ground) x 4. Should be good to prove the concept. Fine tunning we do later. I hope you agree? Regards,


#73

Hi @Zack @srdjan

This is my test. I am using LimeSDR-Mini as the signal generator, and a mini-circuit signal splitter. I am still using attenuator (5db+10db), because I find limesdr mini would send a high level signal at the beginning of transmission for calibration, which would saturate the receiver.

In my test, I found the phase jumping is even more severe than when I was testing with walkie-talkie. But channel 0 and channel 1 is still more stable than channel 1 and channel 2.


#74

Are you having any underflows? That would kill your coherence no questions asked.


#75

How to determine whether underflow is happening? I am directly calling LMS API, instead of through gnuradio, so no UUUUU or OOOOO showing up.

I think for LMS API, if something like that happened, it should also print something in terminal right? But there isn’t, you can see on my terminal in the video. Plus I am using a rather fast computer, its processor is E5, and the sampling rate is only 10MHz per channel.


#76

I think it’s possible, even if two limesdr-usb isn’t synchronized with the same clock. It’s similar as what I am doing now, only the 2 antennae in diagonal is synchronized, and I am currently doing 2 sets of 2 channel DOA, combining their result into 360 degree.

The shortage of that is without 4 channel synchronized, I can’t detect 3 incoming signal simultaneously, and only azimuth angle is detected.


#77

Thank You Shao,
I am expecting the same result.

Such approach can be useful for my SAR application.
If you imagine aircraft flying in the sector where someone is
expecting assistance. With 3-4 full heading sample, out of simple
“S” turn on course you can narrow exact location with certain probability.