Passive Radar Experimentation: Help Requested

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andrew_w
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Joined: Sun Jan 24, 2021 3:18 am

Passive Radar Experimentation: Help Requested

Post by andrew_w » Fri Jan 29, 2021 3:03 am

Hello! First: I really like the Kerberos and the different projects I’ve seen with it. Big thanks to everyone who has worked on this and posted about projects they have done with it. I’m trying to experiment with the Kerberos in its passive radar mode, and could use some advice with my setup, as so far I have not been successful with it. I live in the United States and am trying to use it with FM radio stations. To date, I have not gotten a really clean Range Doppler Map, and could use some suggestions about next steps. Quick overview of my setup:

For the reference antenna I am using the dipole antenna that comes with the rtl-sdr.com kit.
For the surveillance antenna I am using a directional Yagi antenna.
I am currently doing the setup indoors (top floor of my house) with the directional antenna either facing to the East or West.
I am running on a Raspberry Pi 4, 8GB RAM with libraries installed (instead of using the default image due to the compatibility issue with the 8GB RAM Raspberry Pi 4)
I have experimented with FM rock, alternative, and R&B stations between 94.7 and 100.9 mHz to the north, south, and east of my location. All of the transmitters have been fairly close (I live in a city) between 6 and 14 miles from my location. Most of the transmitters in the 15-30 mi range broadcast voice stations.

The setup I have experimented with the most looks like this:
Screen Shot 2021-01-28 at 9.54.54 PM.png
Screen Shot 2021-01-28 at 9.54.54 PM.png (1.03 MiB) Viewed 1021 times
My Spectrum displays have generally looked like this.
Screen Shot 2021-01-23 at 10.27.52 PM.png
Screen Shot 2021-01-23 at 10.27.52 PM.png (678.36 KiB) Viewed 1021 times
With the Range Doppler Map cycling between views like the following (will reply in thread with the second image as it looks like I can only post 3 attachments to this messge):
Screen Shot 2021-01-23 at 10.14.12 PM.png
Screen Shot 2021-01-23 at 10.14.12 PM.png (848.04 KiB) Viewed 1021 times
I would greatly appreciate feedback on any or all aspects of this setup. If you think I should get two directional FM antennas, any recommendations on specific antennas would be welcome, as I’m not confident the one I am currently using has a lot of directional differentiation.

Thanks in advance. Despite the lack of success this has been fun to experiment with and learn about the basics of passive radar.
Last edited by andrew_w on Fri Jan 29, 2021 3:10 am, edited 1 time in total.

andrew_w
Posts: 2
Joined: Sun Jan 24, 2021 3:18 am

Re: Passive Radar Experimentation: Help Requested

Post by andrew_w » Fri Jan 29, 2021 3:07 am

Follow up with the cluttered Range Doppler Map that is representative of what I'm seeing as this cycles.
Screen Shot 2021-01-23 at 10.14.34 PM.png
Screen Shot 2021-01-23 at 10.14.34 PM.png (2.26 MiB) Viewed 1015 times

rtlsdrblog
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Re: Passive Radar Experimentation: Help Requested

Post by rtlsdrblog » Wed Feb 10, 2021 2:21 am

Okay some notes that will hopefully help:

1) For the reference antenna you will still definitely need a yagi. You will need to use TWO directional antennas. One points to the transmitter, another towards the reflective objects.

You do not want signals from the reflected objects getting into the reference antenna, and vice versa, you do not want reference signal getting into the surveillance antenna. So this is why you use a directional antenna for both.

2) FM is quite difficult to get good PR results with due to the small bandwidth and non-ideal type of signal that WBFM is.

If you have it in your area, try DVB-T or ATSC or DAB signals. Those work the best. Also it's a lot easier to manage a TV Yagi compared to an FM Yagi.

andrew_hw
Posts: 4
Joined: Wed Feb 24, 2021 11:32 pm

Re: Passive Radar Experimentation: Help Requested

Post by andrew_hw » Sat Apr 03, 2021 11:46 pm

Thanks so much for the above. I do have ATSC in my area, and I now have two Yagi TV antennas. They are much easier to work with! Any suggestions on an ATSC center frequency and bandwidth to experiment with? From a geometry perspective Channels 8 and 34 look promising.

Context: I'm still getting pretty poor results. On one channel I get consistent detections for about 5 seconds when planes are 1-3km away from my location (planes come close to flying over my hose as part of one of the landing approaches to the international airport near me. The aiproirt is about 12-15 miles from my location). But I'm not getting any of the nice track-like detections in the videos (i.e. the plane is detected very briefly when it's almost directly overhead, but that's it). When I'm not getting these very clean results, my display is very noisy with most of the screen looking like noise. Happy to post details about the different settings I've been trying and screensots. But figured I'd start with the general question first.

Thanks in advance.

rtlsdrblog
Site Admin
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Re: Passive Radar Experimentation: Help Requested

Post by rtlsdrblog » Wed Apr 14, 2021 11:27 am

For bandwidth just use the largest available 2.56 MSPS.

Yes screenshots are very helpful to see what you're getting. If you like a map showing the geometry of your setup could help too. And do you have two TV Yagis in your setup now? Make sure that the cables are the same length and low loss.

You might also want to try and get the antennas outdoors. Your house materials could be blocking significant signal, and we're dealing with weak reflections with passive radar.

Another tip: Use rtl_tcp and SDR# first to get optimal gain settings for your reference antenna. You'll probably need to set the gain of the reference antenna much lower than that of the surveillance one.

Another tip is to try using the surveillance antenna in a vertically polarized configuration (mount it vertically). I'm assuming your TV signal is horizontally polarized. The idea here is that the horizontally polarized TV signal will become randomly polarized after reflecting off an object. Placing your surveillance antenna in vertical polarization will then pick up those randomly polarized reflections the same as having it horizontal, BUT you will all attenuating the actual signal on your surveillance channel which is what we want.

andrew_hw
Posts: 4
Joined: Wed Feb 24, 2021 11:32 pm

Re: Passive Radar Experimentation: Help Requested

Post by andrew_hw » Wed Apr 14, 2021 1:32 pm

Thank you! I'll post pictures / more details this weekend.

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