Direction Finding and linking existing KiwiSDRs

Hi All  Interested in linking exiting KiwiSDRs for the location of signals via ToA or TDOA.
Is this possible?   RTL have a similar approach for VHF/UHF signals could we achieve this within the KiwiSDR network or other SDR networks?

Comments

  • too many time variables I would think
  • Hi,

    Take a look at this thread.


    Although it's not available in real time, this may be a step towards it. By processing time stamped off-air recordings and then determining the time difference between each, it may be possible to perform a hyperbolic fix (or similar) on the transmitter location.

    However my maths and coding are not up to the task :-(

    Regards,

    Martin - G8JNJ
  • Accepted Answer
    Recording multiple instances using the Python coded kiwirecorder, in Linux, might require a setup of multiple users. Each user would have Python installed and each user would coordinate the recording frequencies and times with the other users. Of course the users could all be the same person on the same computer. To make the recordings start and stop at the same time, each user would setup a crontab with the start and stop times. 

    The latency of start and stop of these crontab jobs should be quite low, the latency over the Internet of the various KiwiSDR receivers could be quite large and variable on any given Internet feed forking into the user's recordings.  Therefore, I would doubt the feasibility of geographically diverse combined recordings for worldwide direction finding. IF the KiwiSDR being recorded provided frequent time stamps, and if the Kiwirecorder was equipped to start and stop recording according to these time stamps, well then maybe. 

    On the other hand, individual users, using directional antennas, or conventional FM TDoA, could independently provide compass headings to a coordinator, who could then plot those lines on a map and triangulate to approximate the general location of a transmitter.  TDoA might work quite well from a space satellite. Oh well...
    Ron
    KA7U
  • jksjks
    Accepted Answer
    There have been three or four people recently express interest in working on HFDF. Some on here or on Github issues or in private emails to me. I'll try and point everyone to this thread.

    It is important to note that V/UHF DF is significantly different from the HFDF problem due to the issues imposed by the nature of the ionosphere at HF. It is much more complicated than you would expect. But we have this wonderful resource: lots of geographically diverse Kiwi installations and now GPS timestamped IQ data thanks to Christoph's recent work (https://github.com/jks-prv/Beagle_SDR_GPS/issues/130)

    KA7U
  • Accepted Answer
    John states "MUCH"..... as someone who does HF R&D 8-5 on my job, I agree!

  • jksjks
    edited November 25 Accepted Answer
    My 100% speculative guess, with little knowledge about the subject, is that for non-realtime bearings (which would be okay for us but useless for "other" HF users) some sort of statistical methods would make the problem easier. Make lots of measurements over a long period of time and you might be able to identify and minimize the multi-path and doppler problems.

    The lightning detection guys (http://en.blitzortung.org/live_lightning_maps.php) have it working really well at VLF where it's mostly ground wave.

  • Accepted Answer
    GW is a whole different, and easier,  animal than Skywave. I have been studying both of those for a similar work task for about 18 months. Tricky stuff.
  • jksjks
    Accepted Answer
    Christoph's latest post on https://github.com/jks-prv/Beagle_SDR_GPS/issues/130 shows how his GPS timestamps are within 20 usec of DCF77 (77.5 kHz) as received by a couple of Kiwis a few hundred km distant. Really fantastic work!

    KA7U
  • Thank you all, who have responded, there is actually method in my madness.  As the Intruder watch coordinator for NZART here in New Zealand, I have a number of volunteer observers.  I was looking to create a method of using the KiwiSDR receivers with their GPS capabilities to make it easier for identifying interfering signals amonst groups, and individuals.   Currently DF finding is ad hoc, done manually and you can imagine coordination is best of luck in terms attempting to lock down the offending country.   There is plenty of algoriths about, using in commercial systems.  But many of these commercial systems are at least 1 Million Euro with a 24x7 fully resourced team doing that role.  Within the Amateur Radio fraternity, I am looking for a repeatable method, which would enhance our capbailities to identify the interfering source with say Google Earth.  The rationale is given the number of Internet of Things or everything - our world is likely to incur greater interference, and also I would like to improve our reporting capabilities - especially within New Zealand, as the Government of the day does not have a HF monitoring capability at all - but depends on handheld spectrum analysers.  I believe VHF and UHF type RTL methods have been validated, but as you state HF is another thing altogether.  But I will keep trying, anything to create a better way of identifying and coordinating the use of existing equipment, Yagi's directional antenna and correlating these for better method of locating the source would certianly increase our capabilities with better means of liaisitng with authorities.  Another option was to use the WSPR network but if I can use a set of SDRs with GPS, this would certainly improve our current capabiltiies.
  • Accepted Answer
    The current state of the art

    http://www.entropixllc.com/

  • edited November 27 Accepted Answer
    How complex the HF and ionospheric issue is depends on your expectations of accuracy.  Also, these accuracy expectations are going to define other variables that might, or might not, be players.  For example clock jitter measured in 10's of usec.  Since each 10 usec is maybe (simplistically defined) 3 km of error, does 100 usec error, and up to 30 km (60 km if both sample sites have errors in opposite directions), really matter?

    If you only want to determine the area of a transmission, i.e. within a few hundred km, then the ionospheric issue is often not huge.

    If both receive locations in a given pair are experiencing single hop propagation then the altitude of the ionopshere is already factored in between them to some extent.  However if one RX location has single hop and the other has double hop, then the issue could, potentially, be significant.

    I suspect for many users the acceptable accuracy is loose enough that something could pretty easily be done.  Knowing the city of the source is great, but often just the state or even country is good enough for many users.

    For several years I and a few other listeners over at HFUnderground have been using, casually and with no big push, a technique based on audio recordings.  We have often achieve accuracies of under 100 km for targets several thousand km away.  Sometimes accuracy is less, on the order of several hundred km, and occasionally it is better, we have done better than 25 km accuracy.  Even when we have 300+ km errors that still puts us closer than just "I wonder where this signal is from"?

    If a technique could be developed that time tags the audio stream of remotes in some way to an accuracy of +/- 300 usec or better that would be killer.  Even something as simple as a short 1 PPS time tick synced to UTC time in one audio channel (say left channel) and detected audio in the other (say right channel).

    T!
  • Accepted Answer
    Hi All,

    I agree even a 100km accuracy would be a good starting point. The advantage of the KiWi network is that it is farily well distributed so once you have a rough location it should be possible to use other KiWi's closer to the suspected location to obtain a more accurate fix. Alternatively lots of fixes could be combined to produce a good average.

    In the UK the radio regulatory body (OFCOM) has a distributed network of 24 remote receiver sites with 20MHz to 3/6GHz DF capability. I believe this uses Keysight / Aligent N6841A units as demo'd in the video linked below.



    Some more background info can be found here


    Some of the research before OFCOM deployed the current network.


    Token - I could add a PPS marker to my KiWi which could be switched in by means of the antenna switch option if this would help with any project. I think Peter, G3PLX, came up with this idea some time ago and I'm keeping him informed about the KiWi enhancements WRT TOA DF'ing as I know this was (and may still be) of interest to the IARU and other National Societies.

    Regards,

    Martin - G8JNJ











    KA7U
  • jksjks
    Accepted Answer
    Wow -- check Christoph's latest post: https://github.com/jks-prv/Beagle_SDR_GPS/issues/130#issuecomment-347206064

    It's a plot of a ground wave TDoA solution for DCF77 using three Kiwis relatively close by.

    KA7UZL1GWE
  • Thank you Martin - I have initiated a project with IARUMS Manager and to liaise with Region 1 and Region 3 - Region 2 appears to be off-line.  Getting the project engine initiated and will update later.
  • Hi John (ZL1GWE),

    Great stuff - John and Christoph are doing some really interesting work here - So our thanks are definately due to both of them.

    Regards,

    Martin - G8JNJ
  • Some recent examples of TDoA measurements can be found here:
    SM2BYC
  • Excellent is DFC77 likely to be detected here?  Or would you advise connect, only connect to KiwiSDR receivers synchronised to this system?  Could be a disadvantage to us in Asia-Pacific? 
  • Hi John (ZL1GWE),

    I'm not sure if you intended to send your last post ?

    However the use of DF77 (time station) was just for test purposes as it's location was known, it was a stable time reference which was useful for calibration and being such a low frequency provides surface wave coverage over much of Europe.

    As others have already pointed out, trying to locate transmitter sites via skywave is a LOT more difficult.

    What Christoph has achieved so far is absolutely spectacular, but it's still a very long way to go before he has a working system with a good degree of accuracy, that is simple enough for the average listener to be able to use.

    At my request he has performed some further tests to try and identify a particular source of interference that can be heard in Europe. Although he has produced some promising looking results, it's not clear if they are correct as we don't know where the actual transmitter site is located. Hmm, I should have thought of that before I asked :-( 

    So to mix a few metaphors, with this test we have a 'chicken and egg situation' where we don't know if the software is producing the correct results or iwhere the real source is to validate it. I think my prompting may have inadvertently persuaded Christoph to 'run before he could walk'.

    I suspect that any further tests will have to concentrate on known transmitter sites, until Christoph has a good degree of confidence in the result that is produced.

    Even assuming that signals propagating by sky wave can be traced to their source, it is likely that this may initially only be possible with 'simple' signals such as low speed data or those that have a strong coherent component. Signal such as SSB voice present a lot of additional challenges.

    I think that Christophs work so far is outstanding, and really hope that it can be further developed as a resource that is available to the amateur community.

    Exciting times.

    Regards,

    Martin - G8JNJ










  • Hi Martin

    Thanks very much for the explanation and update.  Fully understand the vagaries of HF as a communications officer in a past life.   But yes, indeed a wonderful piece of work, especially in the amateur community.

    Hopefully, some of the issues can be resolved with known good sources, and ironed out.   But all and all this is far more promising than when I first started out.

    73

    de ZL1GWE

    John
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