Radio location possible with multiple RTL-SDR's?

[ki7fk]

I have a thought I want to throw out here. I am wondering how difficult it would be for a group of us to use RTL-SDR’s to receive signals from our various locations and upload the signal strength to a web site that would analyze and map transmitter locations in near real-time. It would be somewhat like PSK Reporter, but more regional in map plotting.

It would be useful in locating rouge signals and even lost people that may have transceivers. I suppose it could be used on trunked systems monitoring the input frequencies as well. Maybe require participation for viewing the maps to encourage enough users to get more accurate results?

Anyway, this is beyond my ability to design, but was wondering what others think about the viability of such a radio location project. It seems pretty doable to me, but I am probably missing a few key elements.

Happy New Year to all

 

[nd5y]

A while back there were articles about doing that on hackaday.com and rtl-sdr.com.

 

[kma371]

I have a thought I want to throw out here. I am wondering how difficult it would be for a group of us to use RTL-SDR’s to receive signals from our various locations and upload the signal strength to a web site that would analyze and map transmitter locations in near real-time. It would be somewhat like PSK Reporter, but more regional in map plotting.

It would be useful in locating rouge signals and even lost people that may have transceivers. I suppose it could be used on trunked systems monitoring the input frequencies as well. Maybe require participation for viewing the maps to encourage enough users to get more accurate results?

Anyway, this is beyond my ability to design, but was wondering what others think about the viability of such a radio location project. It seems pretty doable to me, but I am probably missing a few key elements.

Happy New Year to all

Kiwisdr does this
KiwiSDR TDoA Direction Finding Now Freely Available for Public Use

 

[ki7fk]

Intersting, but appears to be only HF below 30 MHz. I was hoping for VHF/UHF radio location.

 

[Token]

Intersting, but appears to be only HF below 30 MHz. I was hoping for VHF/UHF radio location.

The same techniques work fine at any frequency, including VHF/UHF. The Kiwi answer is just an off-the-shelf, in-place solution. TDOA / MLAT is the way to do it, not signal strength. Signal strength can be misleading, while MLAT will get you the right answer with far greater accuracy.

T!

 

[willstuder]

I am VERY new to SDR, but I do have two of the RTL-SDR's which are connected to my scanner discone antenna and even fed with an amp, along with my other two scanners. I am capable of picking up about a 40 mile radius of Hermiston and sometimes more depending on elevation of what I am receiving.

I don't know if my location is something you are interested in and if you feel like teaching a newbie, but I all in if I can help in any way.

 

[slicerwizard]

Intersting, but appears to be only HF below 30 MHz. I was hoping for VHF/UHF radio location.

Then read the articles on rtl-sdr.com

 

[Tom_Neverwinter]

A²+b²=c² radio A and B signal strength = approximate range of radio C

 

[Token]

A²+b²=c² radio A and B signal strength = approximate range of radio C

Wrong on so many levels. Pythagoras theorem simply has no application in this way.

Leaving out the fact the geometry is bad, what happens when A is a 5 Watt HT, B is a 50 Watt mobile, and C is a 50 Watt base station with a directional antenna?

T!

 

[Tom_Neverwinter]

Wrong on so many levels. Pythagoras theorem simply has no application in this way.

Leaving out the fact the geometry is bad, what happens when A is a 5 Watt HT, B is a 50 Watt mobile, and C is a 50 Watt base station with a directional antenna?

T!

you control a and b you are searching for C which is broadcasting. if you want to get into the "nitty gritty", yes the math becomes more complicated. K.I.S.S.

 

[prcguy]

Signal strength alone would not get you any useful direction information, even if you had full control of A and B to find C. You can use time of arrival between several receiving stations, or angle of intercept, but signal strength has little bearing on those methods. In this age where nearly unlimited smarts are available for direction finding systems, there are no signal strength only methods used that I know of.

you control a and b you are searching for C which is broadcasting. if you want to get into the "nitty gritty", yes the math becomes more complicated. K.I.S.S.

 

[Token]

you control a and b you are searching for C which is broadcasting. if you want to get into the "nitty gritty", yes the math becomes more complicated. K.I.S.S.

Even if you have complete control of the EIRP of A and B (transmitter power, antenna gain in a specific direction, and feedline losses) and 100% knowledge of their locations, there is no relationship to the unknown C. Further, if you do know the EIRP of C you do not need A or B to find the range to C, space loss will give you the answer.

T!

 

[prcguy]

Free space loss is just that, loss in free space. Loss over terra firma with ground bounce and reflections off things is completely different and can add up to 6dB gain or loss exceeding 20dB from multipath reflections. Ever been in your car listening to an FM station as you come to a stop and it rapidly goes from full quieting to noise every 6ft or so? That is multipath in action, not fading due to weak signal but strong signals fading due to multiple reflections arriving out of phase and canceling each other.

Even if you have complete control of the EIRP of A and B (transmitter power, antenna gain in a specific direction, and feedline losses) and 100% knowledge of their locations, there is no relationship to the unknown C. Further, if you do know the EIRP of C you do not need A or B to find the range to C, space loss will give you the answer.

T!

 

[mancow]

KerberosSDR - 4x Coherent RTL-SDR

 

[Token]

Free space loss is just that, loss in free space. Loss over terra firma with ground bounce and reflections off things is completely different and can add up to 6dB gain or loss exceeding 20dB from multipath reflections. Ever been in your car listening to an FM station as you come to a stop and it rapidly goes from full quieting to noise every 6ft or so? That is multipath in action, not fading due to weak signal but strong signals fading due to multiple reflections arriving out of phase and canceling each other.

Yes, I am familiar with multipath, I deal with it or have to consider it pretty much every working day.

My example was in response to the suggestion "approximate range to radio C", and space loss can be used to calculate "approximate" range if you do, in fact, know EIRP. It certainly will result in a better answer then whatever was meant by "A²+b²=c² radio A and B signal strength = approximate range of radio C", and that was the point of my mentioning it.

Yes, the factors you mention are real, however by averaging over time, particularly if you are in motion or using directional receive antennas, you can minimize those factors. In EW applications space loss is often used (more so in the past than today) to approximate distance to targets of known EIRP, even given those variables. It has always been used less in COMINT and more often in ELINT, but is applicable to both. You could easily determine minimum distance (not closer than). Yes, absolutely, it is an approximation only, subject to errors, but that does not mean it is useless.

No, I would not primarily use such a technique if others are available. I might use it as a discriminent or a sanity check. And it has little application to the question posed in this thread, since the goal was not range to a transmitter, but rather location, and while you can't have location without a range you certainly can know a range and not have a location defined.

T!

 

[madskilz78]

Have you guys heard of KerberosSDR? It has four RTL-SDR dongles and is designed for RDF. KerberosSDR - 4x Coherent RTL-SDR

 

[dickie757]

I found this thread by searching for ki7fk. I am ki7ebv. We had a qso on the local YSF repeater.

I have a kerberossdr

I get what tom never winter is saying. a= one listening station b= other listening station. Getting the time sync'd between the two stations would be ¿hard?

Greg, I need your advice about YSF. Keep an eye out for a thread about YSF in C.O.

 

[majoco]

Having carried out searches for ELB's on 121.5MHz when that was the emergency frequency, I can tell you that it's not easy, even with proper airborne DF equipment. Two spaced antennas either side of the fuselage so that one is screened from the other, the receiver compares phase rather than signal strength although strength is indicated so that you are approaching the transmitter rather than going away from it. Multipath re-radiation of the signal from large masses on flat land, no direct path to the transmitter if it's lost in a valley, all sorts of problems. The best you can do is find the loss of signal in the overhead and then search for it again at 90 degrees to the previous course and hope you find the overhead again in roughly the same place - then send in a helicopter! At least they can look down and hopefully see that guy waving his yellow jacket!

 

[vagrant]

That KerberosSDR looks like plenty of fun for RDF. Also, that passive radar feature looks pretty good, considering the low dollar cost of it all. Something new to play with. Even as an all-in-one device with four receivers, one could simultaneously use it for ADS-B, APRS, Weather Satellites, with one to spare for phone or data monitoring. I use those single RTL-SDR dongles with a TCXO now for APRS and other stuff, so that $130 price is fair.