Participation of Kiwis in the TDoA process

This discussion was created from comments split from: TDoA Successes.


  • I appreciate the addition of the TDoA extension but I see a potential issue; it can tie up a lot of receivers for a lot of the time. My log shows a good deal of activity which while I don't mind it, I would rather like to limit how much of my kiwi(s) resources are made available for the service.
    One of my main applications of the kiwis, here at N6GN as well as at KPH, AI6VN/KH6 and elsewhere is to understand and improve the dynamic range limitations due to noise. If/when most of the resources are involved in TDoA and no longer available, this can become difficult.

    How does anyone feel about the possible addition of a limit to how many receivers may run TDoA
  • "How does anyone feel about the possible addition of a limit to how many receivers may run TDoA"

    Seems like a sensible idea to me.

    There may also be potential political problems in some countries e.g. if a KiWi on 'their' territory is used to TDoA military facilities.

    On a similar subject - I notice that users IP addresses are now no longer shown on the KiWi GUI (they may still be logged) but just the approximate location instead. I think this is sensible too.


    Martin - G8JNJ
  • @N6GN, @G8JNJ
    I am also in favour of limiting the Kiwi channels available for TDoA service, perhaps with the exception of the administrator. It has been suggested to somehow dynamically show which Kiwis contribute best to the TDoA solutions. While this would be convenient it will no doubt also increase the number of requests to those Kiwis.

    "Political problems in some countries" are indeed a concern. I noticed that using a few specific Kiwis
    there is almost a systematic offset in their LOPs (lines of position), which could be due to their own reported position being obfuscated on purpose. I hope the operators realise that their location could be fairly easy be deducted from their contribution to a couple of TDoA solutions of known stations.

    73, Ben
  • I have plans to add a menu in the (future) TDoA section of the admin extension tab. It will allow you to limit the number of simultaneous channels the TDoA service from may use.

    However this won't preclude other applications (including, say, directTDoA by linkz) connecting. For that I propose adding an option that removes GPS timestamps from the IQ output stream entirely. It might even be advisable to include an option to disable connections from anything other than the KiwiSDR browser UI. Although how you do that in a manner that can't be spoofed is something I don't understand at the moment.
  • Re: IP addresses not being shown in the "users" tab. I think I made that change 18 months ago.
  • edited July 2018
    Hi John,

    The first step you mention would be a good start to limit outside TDoA requests via the extension if necessary to zero. The other one is more drastic of course.

    Just hope that only Kiwi owners in those places that are concerned about their personal safety will use such measures when available and everyone else stays on. Actually would be great to see more usable Kiwis.

    Looking at the dynamic SNR maps created at and it is a pity that some sites with very decent SNRs do not have sufficient GPS reception to timestamp their IQ output stream.
    Just wonder if a batch of low loss ready made GPS extension cables could help with locating their GPS antenna more favourable. Perhaps something for Seeed to look at as an accessory.

    73, Ben
  • jksjks
    edited July 2018
    To keep the base cost of the Kiwi as low as possible we had to bundle a very inexpensive GPS antenna. I think the 3m cable length is a real problem for most people. It's tough enough to get that near a window let alone outside and in the clear. So your idea about offering a cable extension is a good one. I wanted Seeed to do the same with a linear power supply but we never got there.

    Some of the good-SNR Kiwi owners might not have seen the point of installing the GPS antenna originally. Perhaps all we have to do now is ask if they'll reconsider.
  • "Some of the good-SNR Kiwi owners might not have seen the point of installing the GPS antenna originally. Perhaps all we have to do now is ask if they'll reconsider."

    Agreed, I think it would be a good idea for KiWi Users and Admins to email some of the 'key' KiWi Admins to see if it's possible to help them get the GPS running, and also in some cases try and sort out some of the interference problems. I've done this in the past with good results.

    John - Maybe these discussions need to be moved to the TDoA UI improvements thread ?


    Martin - G8JNJ
  • jksjks
    edited July 2018
    @Martin: I would, except that this crappy forum software only lets you split and move a set of messages into a new topic. I can't move messages individually to existing topics unfortunately. But let me start a new topic..
  • I took a quick look at the log to see what impact TDoA service has on my KiwiSDR's.
    root@kiwisdr:/var/log# cat user.log |grep -i TDoA |grep -i leaving
    It appears in my case that most of the usage is from the same user, and while the uses are repetitive and usually for the same frequency, the total impact to the overall availability of the KiwiSDR is quite limited. I have not yet attempted to see if the KiwiSDR is actually fully occupied at different times and for how long. I suspect the full usage times will be with other than TDoA users. I need to figure out a script to list the full usage occurrences to be able to monitor that.
    Ron - KA7U
  • It's hard to assess the user as Fremont CA station is the server and could be anyone who pointed it toward me.
  • Another thought WRT TDoA usage.

    Maybe folks using an 'admin' account or password would get priority over a TDoA request (or perhaps even general useage) and kick it ?

    This would allow folks like N6GN and others who use their KiWi's for other monitoring purposes (which take priority) to still make the KiWi available, but they would get instant access for their own activities.

    Hmm.... I'd quite like to be able to do this on my own KiWi sometimes. When I do have to kick users, I generally pick the ones that have been using it for the longest period, or who are listening to UK BC stations that they could hear a lot better via the broadcasters own internet stream and not tie up a user channel :-(


    Martin - G8JNJ
  • Another success today - I emailed Esteban, EA8DGL, and asked if he could enable his GPS as he's in a great location for TDoA in the Canary Islands just of the West coast of Africa.

    He very kindly did this today and he's now appearing on the TDoA map :-)

    The other good news is that he's just got his Amateur licence and permission to put a better antenna up, so hopefully reception will soon be even better.

    My thanks to Esteban for doing this.

    If anyone else feels like emailing other KiWi owners in key locations that would be very helpful too.

    Maybe we should compile a 'hit' list ?


    Martin - G8JNJ
  • I am currently working with friends to get systems working in Singapore and NE Maine
  • I have two KIWI's on line from here, and maybe more coming, but only one connected with a decent view for any GPS satellites. It seems the one without the GPS shows up on top and because no GPS there is enough difference in their positions if one zooms in far enough. If I do get the other one on GPS, I wonder if the dither (added) will make it easier or harder to select the bottom one?

    My main question is on the GPS - I have a 5 way splitter (gd to 2150 mhz) with one DC pass thru port. Will I be able to connect the GPS of multiple KIWI's to this splitter? Do the KIWI GPS's require a load to trick them into thinking they have a proper GPS connection... if so how many ohms?

    Thanks, Don
  • jksjks
    edited July 2018
    @ve6jy: I don't quite understand. "It seems the one without the GPS shows up on top". Which map are you talking about here? Not the TDoA map because that one should only be showing VE6SLP/VE6JY since the other (VE6JY) doesn't have GPS currently. And that's what I'm seeing.

    There is an argument for making the dithering much greater so you don't have to zoom in so far to make stations with identical locations selectable. You only care about the general location of the Kiwi anyway. The alternative is to replace the "tooltip" list that appears when you mouseover the round marker cluster icons with a little menu that has selectable entries. But it will take some work to do that and I haven't had time yet.

    Minimum 3.3V load on GPS port for antenna detection: This won't be a problem. This was the last bug that caused the final PCB spin. In some photos you see PCBs dated "March 2016". But everyone, except some beta sites, should have PCBs that say "May 2016". A 10k resistor was added across the antenna bias pin of the GPS front-end chip (see schematic) so that it always thinks there is an antenna connected. This is necessary for the case you point out: the Kiwi is connected to a passive splitter port that is drawing no 3.3V load. With no load the chip switches to another input that isn't connected to anything. And there was no way to disable this behavior in software. So, board spin required..

    Is that a 5:1 passive splitter? If so, be careful about using the supplied puck antenna and its lossy 3m of RG174. Better to use an active splitter or an antenna with better gain (e.g. +40 dB) and less lossy coax.
  • It's the ratings map at but I assume it will be similar with the TDOA map if I get the 2nd gps up.

    Yes it's passive. I have a GPS 10 mhz unit (Leo Bodnar one), maybe it has more gain.
  • I can see that some users don't want to participate in the TDoA but I'm in the other camp where I would rather not have normal users when local QRM is too bad but if someone wants to use it for TDoA, and it works, that's fine.
    Maybe we could have a "Short Stay" channel where the priority is TDoA or protected via password generated from the central server?

    Another slightly off topic idea, crowd funded KiwiSDR installs in places of interest. A user proves they have decent internet access and can set up GPS and RX antenna and then users chip in small amounts to illuminate that bit of the world. The money goes to the manufacturer not the user and the kit is released only when the full cost is raised OR a percentage together with enough interest in the location shown.
  • Re crowd-funded Kiwi installs in desirable locations: Be a little bit careful about that. I spent roughly US $6500 sending out 20+ Kiwis over an 18 month period since the Kickstarter. Only about half of them are still operating today. On the other hand, 8 of 9 beta Kiwis I sent are still operating.
  • Understood on the crowd funding, it is too easy to look at a problem with our own motivations. I did think maybe schools could be persuaded then there is someone responsible and the teaching side is an on-going motivator.
  • I use one of these (see eBay): GPS Antenna Signal Repeater Amplifier Receiver Active For Car Phone navigation. The external GPS antenna is on the shack roof, the internal antenna radiates the GPS signals around the shack for pick up by KiwiSDR, GPSDO etc etc. each device must be fitted with its own GPS antenna - but you get one included wih Kiwis and most eBay GPS modules.
  • jksjks
    edited July 2018
    GPS signal repeater? Yikes. It is necessary for us (KiwiSDR) to be extremely clear about that for liability reasons. Most countries require you to have a license to operate such a device and for the device to be type-accepted (or whatever the terminology is in your particular country). This is an attempt to keep shoddy devices off the market and also have a registry of known devices in case there is a problem with GPS reception in your area that needs to be addressed quickly. Example:

    I personally would not use such a device if I lived anywhere near an airport. If there's a precision approach mishap and someone goes looking for and finds your unlicensed repeater they will hang you from the nearest tree. And they won't care about 1/r^2 and how it's "impossible" that your device caused a problem.
  • edited July 2018
    I am currently working with friends to get systems working in Singapore and NE Maine project is slow. Neither friend is a radio buff :-(
  • Thanks JKS - it was interesting to read the Ofcom statement and licensing arrangements. I have, of course, disabled my system and now run all the GPS antennas outside.
  • I don't mean to be too extreme about this. But problems with GPS antennas and reception is an ongoing issue for many Kiwi installations. And I just want people to be aware of the consequences of using this kind of solution. Technically it's very tempting. But you're taking a big gamble on the signal quality and power level emitted by those kind of devices. And without the proper test equipment to actually measure them it's tough to judge.
  • I agree. Given the developing capabilities of the KiwiSDR network especially TDoA and the publicity its getting, the operation has to be squeaky clean w.r.t. international and national regulations. It really was interesting to read the CEPT ECC Reports 129 & 145, ETSI EN 302 645 and NTIA Redbook section 8.3.28. Certainly enough information to provide an insight and warning of the consequences.

    The problem still remains though - how to run multiple indoor-devices requiring GPS without installing separate outside antennas for each device.
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