Direction finding for intermittent signal

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GrouchoDuke
Posts: 6
Joined: Fri Mar 15, 2019 7:09 pm

Direction finding for intermittent signal

Post by GrouchoDuke » Wed Apr 10, 2019 5:43 am

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!

rtlsdrblog
Site Admin
Posts: 2427
Joined: Mon Nov 19, 2012 11:54 pm

Re: Direction finding for intermittent signal

Post by rtlsdrblog » Wed Apr 10, 2019 10:14 am

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.

mdacosta
Posts: 17
Joined: Mon Mar 18, 2019 6:27 pm

Re: Direction finding for intermittent signal

Post by mdacosta » Wed Apr 10, 2019 3:07 pm

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".

GrouchoDuke
Posts: 6
Joined: Fri Mar 15, 2019 7:09 pm

Re: Direction finding for intermittent signal

Post by GrouchoDuke » 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!

rtlsdrblog
Site Admin
Posts: 2427
Joined: Mon Nov 19, 2012 11:54 pm

Re: Direction finding for intermittent signal

Post by rtlsdrblog » Wed Apr 10, 2019 11:22 pm

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.

GrouchoDuke
Posts: 6
Joined: Fri Mar 15, 2019 7:09 pm

Re: Direction finding for intermittent signal

Post by GrouchoDuke » Thu Apr 11, 2019 1:22 am

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!

253flo
Posts: 14
Joined: Mon Apr 22, 2019 6:20 pm

Re: Direction finding for intermittent signal

Post by 253flo » Sat May 18, 2019 9:06 pm

DFing intermittent signals is a must have capability.

rtlsdrblog
Site Admin
Posts: 2427
Joined: Mon Nov 19, 2012 11:54 pm

Re: Direction finding for intermittent signal

Post by rtlsdrblog » Tue May 21, 2019 6:02 am

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.

GrouchoDuke
Posts: 6
Joined: Fri Mar 15, 2019 7:09 pm

Re: Direction finding for intermittent signal

Post by GrouchoDuke » Fri May 24, 2019 5:48 am

Thanks for adding this in. I'm hoping to use this for a high power rocket tracker this weekend.

myke
Posts: 37
Joined: Wed Aug 28, 2019 7:03 pm

Re: Direction finding for intermittent signal

Post by myke » Wed Aug 28, 2019 7:34 pm

Bumping a month+ old subject here - but wondering how much was accomplished with intermittent signal locating in Pi image 1.4 .. I can see where the sampling rate would help considerably short of a SNR, min pwr or squelch setting ... or is this resolved with the confidence indicator on a heat map? (looking forward to getting my hands on a board!!!)

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