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Passive Radar.
#1
I have been playing with a passive radar setup at home. A side project to the AIS receiver. I live near an airport and can see the traffic come and go they are a little bit of a PITA to wire and tune but I did get it working. The good news is RTL-SDR is coming out with a 4 channel receiver. One of my concerns with passive radar is how it will perform in a moving vessel. Where you would either have to reposition the reference antenna or would have varying input of the reference signal. But with a 4 channel I think the extra inputs could not only help with the dimensional reflection but help in keeping that reference signal more stable.


Has anyone put this to use in a moving vehicle?


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#2
Are you detecting radar from other vessels? What frequencies are you using? Why would 4 inputs help? Couldn't you use multiple rtlsdr dongles instead?
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#3
(2019-01-22, 12:54 AM)seandepagnier Wrote: Are you detecting radar from other vessels? What frequencies are you using? Why would 4 inputs help? Couldn't you use multiple rtlsdr dongles instead?


No you are using a known large radio source as a reference point. TV or Radio station. With a semi directional or directional antenna pointed at the station. You are using another antenna to listen for the same fm station but from a reflection slightly later than the first known reference signal. The dongles need to be altered so they are all using the same clock timing. Not individual clock timings to accurately measure the Delay. You need at least 2 inputs but I was thinking with 4 you would have better coverage and a better idea of the exact direction of the target as you would have different reflection rates. My other thought was writing a quick scan every 30 seconds of the reference signal strength to change the reference antenna on the fly Incase you changed course and a different antenna should now be the reference antenna.

Hope that makes sense.


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#4
http://jmfriedt.free.fr/URSI.pdf


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#5
Are you using the FM stations reflected off a ship to find where the ship is?

I think it would be a lot more interesting to detect normal ship radar, but this would need a down-converter.. has anyone tried it?
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#6
(2019-01-23, 05:07 AM)seandepagnier Wrote: Are you using the FM stations reflected off a ship to find where the ship is?

I think it would be a lot more interesting to detect normal ship radar, but this would need a down-converter.. has anyone tried it?
Most larger ships running radar already have AIS. I want to be able to detect smaller ships without radar and islands ect.


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Fm or TV stations yes. They are my transmitter. You could definitely use the same set up as a radio direction finder to pinpoint other ships active radar. Very similar hardware setup just wouldn’t need to be on the same clock crystal.


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#7
i was looking at these receivers for weather fax but i didn't find enough info on them.
http://www.elektronik-labor.de/HF/DSPM2.html

https://www.ebay.com/itm/DSPM2-FM-Stereo...4902.l9144
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#8
I use an RTL-SDR dongle by nooelec. I do believe they do weatherfax but haven’t played with it yet.


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