Phase coherent IQ samples for a Windows program

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ClintMclean
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Joined: Thu Oct 17, 2019 5:12 pm

Phase coherent IQ samples for a Windows program

Post by ClintMclean » Thu Oct 17, 2019 5:14 pm

Hi,

I received the kerberos sdr a few weeks ago and now I just need the phase coherent IQ samples from each of the rtl-sdrs so that I can get it working with a windows program that I wrote.

How would I do this?

myke
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Joined: Wed Aug 28, 2019 7:03 pm

Re: Phase coherent IQ samples for a Windows program

Post by myke » Sun Oct 20, 2019 5:25 pm

Take a look at the Receiver @ https://github.com/rtlsdrblog/kerbeross ... eceiver.py

line 192 would be a good start I think.... #np.save("hydra_raw.npy",self.iq_samples)

Windows development - what's your goal?

rtlsdrblog
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Re: Phase coherent IQ samples for a Windows program

Post by rtlsdrblog » Tue Oct 22, 2019 9:41 am

Yep for now you'll need to modify the code yourself, or simply pipe out the stream from the run.sh before it goes into the Python program. But either way you'll need to modify the code for that.

In the future software version (still several months away), we'll have the coherent stream easily accessible via a TCP connection.

ClintMclean
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Re: Phase coherent IQ samples for a Windows program

Post by ClintMclean » Thu Nov 14, 2019 5:38 pm

Thanks Guys

I've got the kerberos c code compiled and working in Visual Studio.

I also wrote some code to calculate the amount to shift a signal so that it's synchronized with another signal.

Now though, I've found that it seems to only generate noise for the first rtl sdr.

In the code at line 367:

https://github.com/rtlsdrblog/kerbeross ... /rtl_daq.c

it also seems to only connect the first rtl sdr to the noise source.

367: rtl_rec = &rtl_receivers[0];

Shouldn't it generate noise on all of them so that the same signal can be synchronised?

Also, the rtl sdr still seems to be able to receive an FM signal with the noise.

Is that the way it's designed, it doesn't affect the synchronisation?

rtlsdrblog
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Re: Phase coherent IQ samples for a Windows program

Post by rtlsdrblog » Fri Nov 15, 2019 2:38 am

The noise source is activated by the GPIO on RTL-SDR #0. The noise source is hard wired to provide noise equally to all RTL-SDRs on board.

It's not powerful enough to overcome strong signals like BCFM. You should disconnect the antennas first when calibrating to ensure that strong signals don't corrupt your phase sync.

AE6EO
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Re: Phase coherent IQ samples for a Windows program

Post by AE6EO » Sat Nov 16, 2019 3:09 am

By any chance, is this GPIO also plumbed out to one of the contacts on the 40-pin header?

I'm tempted to build a small external antenna connect/disconnect board - I have some nice SMT 50-ohm surface-mount relays that I think might pass the RF through cleanly enough to not disrupt the DOA process. I'll need some form of driver for the relays of course (can't drive directly from any GPIO with safety!). I can do this with a simple external toggle switch, but it'd be convenient to have the antennas connect and disconnect automatically when the noise source is switched.

If not I'll probably use one of the GPIOs on the La Frite server board, and hack the GUI script handler to toggle this in sync with the RTL GPIO.

rtlsdrblog
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Re: Phase coherent IQ samples for a Windows program

Post by rtlsdrblog » Sat Nov 16, 2019 7:45 am

Unfortunately not, the header only contains power. I'll double check with the hardware designer if there's any other good place to tap the GPIO.

Will be keen to see your results with the relays. We have someone working on a design with silicon switches as a prototype test for a future KerberosSDR V2.

If it works without distortion we'll see how difficult it would be to have a retrofit calibration board with switches built in for V1 owners.

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