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Direction finding for intermittent signal

Posted: Wed Apr 10, 2019 5:43 am
by GrouchoDuke
I'm trying to track a radio beacon that transmits for 0.5seconds every 5 seconds. (So, the signal is 0.5sec on, 4.5sec off.) I'm using v1.2 of the Raspberry Pi software.

When I use the compass webpage on the Pi or the Compass Android app, it looks like the arrow points toward the signal just after it transmits. However, for the other 90% of the cycle time, the arrow bounces around all over the place. This makes it pretty much impossible to figure out which direction the radio transmitter is.

Is there a way to only update the compass solution when there's a signal over a certain strength? It'd be great if the compass showed the last good solution for a signal over some threshold strength and maybe also showed the time since the last update.

Thanks!

Re: Direction finding for intermittent signal

Posted: Wed Apr 10, 2019 10:14 am
by rtlsdrblog
Sorry at the moment we don't have any way to handle intermittent signals. That would be something that you'd need to implement yourself in the open source code. We'll look into the possibility of doing this ourselves, but I can't guarantee that it's soon.

Re: Direction finding for intermittent signal

Posted: Wed Apr 10, 2019 3:07 pm
by mdacosta
GrouchoDuke, I'm also trying to find intermittent beacons. I suggest you play with the Sample Size settings under the DOA Estimation page, right under the Corr. Matrix. I found that a smaller Sample Size will result in a slower moving arrow so you won't see much "jumping around".

Re: Direction finding for intermittent signal

Posted: Wed Apr 10, 2019 4:40 pm
by GrouchoDuke
Thanks to both of you. I'll try the sample size first to see how that impacts things with my transmitter.

For the code to do modify the compass calcs to not update when the signal is below a threshold, do you mind pointing me to where I could add that? I made it as far as estimate_DOA in hydra_signal_processor.py.

Thanks!

Re: Direction finding for intermittent signal

Posted: Wed Apr 10, 2019 11:22 pm
by rtlsdrblog
GrouchoDuke wrote:
Wed Apr 10, 2019 4:40 pm
Thanks to both of you. I'll try the sample size first to see how that impacts things with my transmitter.

For the code to do modify the compass calcs to not update when the signal is below a threshold, do you mind pointing me to where I could add that? I made it as far as estimate_DOA in hydra_signal_processor.py.

Thanks!
For the code you could try adding a SNR detection threshold algorithm in the hydra_signal_processor.py code. Setting it to not write to the the HTML file when below a certain threshold.

We're currently thinking about how to add a 'confidence' reading to the DoA results. That might be the ultimate solution as ideally the confidence would be low when there is just noise. Still investigating how to do that.

Re: Direction finding for intermittent signal

Posted: Thu Apr 11, 2019 1:22 am
by GrouchoDuke
Great, thanks. I'll do some more digging in there.

If you come up with anything like you're talking about, I'd love to see that too.

Thanks!

Re: Direction finding for intermittent signal

Posted: Sat May 18, 2019 9:06 pm
by 253flo
DFing intermittent signals is a must have capability.

Re: Direction finding for intermittent signal

Posted: Tue May 21, 2019 6:02 am
by rtlsdrblog
In the latest version we added the possibility for squelch based on power levels to be implemented. For the compass, if you edit the _webDisplay/compass.js file, you'll see the MIN_PWR const at the top.

It works on the PWR values output at IP_ADDR:8081/DOA_value.html

The Android app can also now filter the log by PWR value, so you could remove all low PWR readings.

We're working on a more advanced Android version that would be able to plot the log history in real time.

Re: Direction finding for intermittent signal

Posted: Fri May 24, 2019 5:48 am
by GrouchoDuke
Thanks for adding this in. I'm hoping to use this for a high power rocket tracker this weekend.