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Direction finding issue

Posted: Tue May 07, 2019 2:02 pm
by GermanTerrible
Hello everyone, could you please review this video and the comment?

It seems to be happening to several of us.

Thank you in advance.

Re: Direction finding issue

Posted: Tue May 07, 2019 5:17 pm
by Corrosive
There is really not enough information in your video to be able to provide much help in the matter.
Can you make another video showing the entire setup?

Antennas, distance, settings and signal source would be very helpful.

Re: Direction finding issue

Posted: Tue May 07, 2019 6:25 pm
by GermanTerrible
I am sorry but it is not possible. The video is not mine but another user's, I am just suffering the same problem. As I explained in my comment in, it is not easy for me to perform extra tests these days. The youtube user published some other videos but his setup is not shown. I will further describe mine.

I tried using four dipoles as antenna array and looked for the DoA of the Madrid TV tower. The approximate frequency could be about 770 MHz. I tried mostly ULA with 0.3 lambda spacing.

After the first test I realised that the four dipoles are not equal to each other, the inner conductor of the coax cable is not always connected to the same half of the dipole. I suppose that this issue inverts the phase of the two affected antennas. In order to avoid confusing myself I decided to remove the "ground" half of each dipole. Then I set up the array, with the "active" half upwards, and repeated the tests; this way I also got bad results.

As I posted in, I suspect multipath issues, I could only perform the tests at home these days, with the array always fixed at the same place. Perhaps such environment is not the best. The compass usually pointed not so far from the tower, but not too exactly, and sometimes it pointed to random directions.

I also suspect the ferrite balun of these antennas is not good enough for this work, because ferrites are not useful at UHF frequencies. If the balun is not working properly, the feed line would be receiving as part of the antenna itself. I have properly separated the dipoles, but not the feed lines as well. I tried moving the feeders and it seemed that the DoA screen graphic changed a lot.

I tried also to DF my ham radio walkie talkie, with 50 mW of power at 435 MHz, with similar results. This test was also performed at home.

This user had published four videos, but unfortunately only a little is seen. Anyway, they are: (you have already seen this one)

Re: Direction finding issue

Posted: Tue May 07, 2019 11:37 pm
by rtlsdrblog
Could you please explain what the issue actually is? Also, i'd definitely need more information about the physical setup, and screenshots of your settings etc. e.g. have you set the decimation/FIR filters? Is the KSDR in proper sample and phase sync?

One thing I saw in your last video though, you've activated every single direction finding algorithm at once. It is recommended to only activate ONE at a time unless you really know what you are doing. Activating all at once will take the average of all the peaks, and if one is wrong the results will be skewed. Notably the Maximum Entropy (MEM) algorithm can often be very wrong in normal use and would certainly skew the average peak.

In most cases the MUSIC algorithm is the one that is able to get closest to the optimal solution.

For the dipoles, just orient them all with the center conductor facing upwards.

Also i'm not sure if it was you or someone else who posted, but in their settings I did see that they left the noise source on by accident. Make sure that the noise source is turned OFF after calibration.

Re: Direction finding issue

Posted: Mon May 13, 2019 6:29 am
by GermanTerrible
Sorry about it. I am tapering the dosage of a pill against anxiety. It is not always easy for me. I will try when I can.

Re: Direction finding issue

Posted: Mon Jun 03, 2019 6:12 am
by GermanTerrible
Sorry again. This weekend I could do more tests. I think it works correctly most of the time, and that only occasionally indicates the wrong direction. I think it's the same behavior that I see in the videos. For now we can close this thread. Thank you.