[hpsdr] Fw: [Discuss-gnuradio] Software Defined Radio Direction Finding (SDRDF)

[Joe Martin K5SO]

Hi Jeff! 

That's very slick!   Thanks for sharing it.   

As you likely know, currently I am working hard trying to develop a suitable direction finding (DF) capability using our multiple-receiver HPSDR rig at HF frequencies.  The YouTube video referenced in your post briefly mentions DF at HF frequencies but, of course, the actual unit shown and demonstrated is working at much higher frequencies than HF.  The magnitude of Doppler shifts are directly proportional to the operating frequency, therefore Doppler-based DF is usually not done at HF;  instead, it is much more common to use Doppler shift DF at VHF and higher frequencies simply because the measured shifts are much larger and therefore the S/N is better.  

At HF, I've been developing a different approach that has been around for some time that is very different from Doppler DF methods, namely, using measured phase-shift differences among three antennas/Mercury receivers to calculate the angle of arrival of the rf wave.  This approach is showing quite good promise except for a "little" problem that, as it turns out, is a fundamental characteristic of our HPSDR radio design.  

The problem centers around the fact that when we start up multiple Mercury boards the relative phase relationships between the receivers is random.  Try and try as I might I have not yet been able to devise a suitable method to force all receivers to be in phase at startup.  I've tried numerous methods to do this, most centered around holding the receivers in "reset" until everything else stabilizes but, while that sort of works it isn't good enough for accurate DF work at HF.  I'm still working hard at this issue and believe I will eventually find a solution that works for our HPSDR radio.  I have a suitable GUI coded already to display everything needed, with a modified v2.2.3 PowerSDR program, so that's ready to roll as soon as I figure out a suitable method to cure the start up phase problem.  

Thanks again for the info!  Good stuff.

73,  Joe K5SO


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