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General Category => General Radio Discussion => Topic started by: ChrisSmolinski on July 13, 2018, 1527 UTC

Title: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: ChrisSmolinski on July 13, 2018, 1527 UTC
As many have no doubt heard by now, the Kiwi SDR network has a new feature, TDoA direction finding. Some details here: https://www.rtl-sdr.com/kiwisdr-tdoa-direction-finding-now-freely-available-for-public-use/

This has caused some... concern in the pirate listening community. Well, more concern from the operators than the listeners, I imagine. This is not a new technique, several of us have been using a variant of this and our own equipment to locate utility stations for some time, see the posts here for example, as we located one of the pips stations: https://www.hfunderground.com/board/index.php/topic,41025.0.html

I won't go into the theory behind how TDoA works, you can read about it online. The purpose of my post is to show some concrete examples of the accuracy of this technique, now that it is available to the masses.

First, here is a plot of the Link-11 military transmission on 6942 kHz, the one that often plagues the 43 meter band:

(https://i.imgur.com/s3zWSva.png)

We did not know the QTH of this transmission, now we do, the northern coast of Florida.


Next, CFRX 6070 from Toronto:

(https://i.imgur.com/bZpaaUk.png)

And finally WTWW 9475 Lebanon TN:

(https://i.imgur.com/SAO2aea.png)

As you can see, the accuracy is such that we can locate the transmitter to the state/province in question, and for larger states, what part of the state. Eyeballing the maps, I would say theres a 50 or so mile accuracy to the location of the transmitter site.  Several orders of magnitude too much to get the transmitter's street address. But enough to determine the nearest nearby large city.

I'll also note that even without techniques such as TDoA, for some time it has been possible for hobbyists to roughly guess where a transmitter is located based on propagation characteristics. Several stations in the past have attempted to spread misinformation about the transmitter site to throw DXers off the trail, this fails pretty miserably. And now with TDoA available to the masses, it will be trivial to locate stations to 50 or 100 miles. That is the fundamental change. And, of course, governments have had far superior direction finding capabilities for some time now.

While some of us have been posting DF maps of broadcast and utility stations, I expect that all users understand that it would be best to refrain from posting any maps of pirate stations.

Still, shortwave pirate radio is going to change in some ways due to this widespread DF capability.  It's impossible to keep this technique "secret", not talking about it and the capabilities won't make it go away. It is better IMHO for everyone to be as informed as possible as to the capabilities and limitations.  Pandora's box is open, there's no closing it.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Josh on July 13, 2018, 1539 UTC
If the privateers weren't mobile before, I doubt the advent of tda will change their operating much. It's not like fcc can't trace a line to a specific tower or fingerprint a transmitter or tell how much rf is being pushed or anything.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Token on July 13, 2018, 1813 UTC
If the privateers weren't mobile before, I doubt the advent of tda will change their operating much. It's not like fcc can't trace a line to a specific tower or fingerprint a transmitter or tell how much rf is being pushed or anything.

The FCC HFDF system uses, as one of its techniques, TDOA to geolocate signals.  This technique has been available to them for years.  And small groups of hobbyist have had the ability for years also.

However now anyone with access to the Kiwi network can do it with various degrees of accuracy.

I don't think this actually increases the danger of prosecution to pirates, but it might make them more uncomfortable.  It is probably more of a perceived issue than a real threat.

T!
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: redhat on July 13, 2018, 2235 UTC
If the privateers weren't mobile before, I doubt the advent of tda will change their operating much. It's not like fcc can't trace a line to a specific tower or fingerprint a transmitter or tell how much rf is being pushed or anything.

The FCC HFDF system uses, as one of its techniques, TDOA to geolocate signals.  This technique has been available to them for years.  And small groups of hobbyist have had the ability for years also.

However now anyone with access to the Kiwi network can do it with various degrees of accuracy.

I don't think this actually increases the danger of prosecution to pirates, but it might make them more uncomfortable.  It is probably more of a perceived issue than a real threat.

T!

I suspect 'business as usual' will proceed in light of this information, however, the notion that this technology is in the hands of the average enthusiast may dissuade those from running pervasive material in a frequent manor.  I myself have received a few threats over the years, and most of what we run is pretty tame.  It does add a degree of unease knowing that the average ham with an axe to grind now has access to an easy way to locate those he doesn't like, licensed and otherwise.

+-RH
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: KaySeeks on July 13, 2018, 2336 UTC
I was waiting for someone to post about this.

It likely won't change anything directly related to enforcement activity but as we know, the authorities tend to work from information given to them and I suppose it might give extra information to someone inclined to report a station for one reason or another and that could get passed on to the authorities.

I have been using it a bit this week on the Kiwi network and I will point out that it's not exactly a "turn-key" or "fire and forget" system - it's not as simple for "the unwashed masses" as driving an automobile yet. I figured out some rules of thumb to increase likelihood of tight convergence through trial and error and I bet a lot of people who aren't as much of an introverted geek as me won't have the patience.  :D
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: BoomboxDX on July 14, 2018, 0537 UTC
Looks like a cool feature for stuff like finding locations of secret government transmissions, but by looking at these "maps" -- which actually are distorted in projection -- they really don't show locations well -- at least for pinpointing a pirate to more than a general area.

The maps have no cities, no roads, no state lines, no county boundaries, no grid squares... They look cool, but unless there is a way for an individual to correlate them to an actual map that has more than continental outlines I sort of doubt they would help any hobbyist or ham pinpoint anything.

Aside from the government transmission mentioned above, the other stations' locations are already known. If I hadn't known CFRX's location already, by looking at that map I'd have no idea if the transmission were in Ontario, western Quebec, Ohio, Indiana, western NY, or Michigan. It's a crummy map for pinpointing anything unless you already know where it is.

That is, unless you're satisfied knowing a transmission came from a certain state that is readily identifiable, as is the case with Florida above.

Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Token on July 14, 2018, 1246 UTC
Looks like a cool feature for stuff like finding locations of secret government transmissions, but by looking at these "maps" -- which actually are distorted in projection -- they really don't show locations well -- at least for pinpointing a pirate to more than a general area.

The maps have no cities, no roads, no state lines, no county boundaries, no grid squares... They look cool, but unless there is a way for an individual to correlate them to an actual map that has more than continental outlines I sort of doubt they would help any hobbyist or ham pinpoint anything.

The system is still under development.  My understanding is one of the hit list items is adding greater detail to the maps.

However, even without that, there are lat and long grids along the sides.  Draw the lines across the page and down the page, read the scales, and you can have lat and long to the center point.  Pop that into Google Earth or Google Maps, and away you go.

T!
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: ChrisSmolinski on July 14, 2018, 1329 UTC
Here's your new and improved map, CFRX 6070 Toronto:

(https://i.imgur.com/6NobNtW.png)
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: BoomboxDX on July 14, 2018, 1433 UTC
Looks like it's off by about 30 miles. Enough to make a pirate a little less hesitant, but obviously the technology will probably improve.  ;D
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: MDK2 on July 14, 2018, 1512 UTC
I suspect 'business as usual' will proceed in light of this information, however, the notion that this technology is in the hands of the average enthusiast may dissuade those from running pervasive material in a frequent manor.  I myself have received a few threats over the years, and most of what we run is pretty tame.  It does add a degree of unease knowing that the average ham with an axe to grind now has access to an easy way to locate those he doesn't like, licensed and otherwise.

+-RH

I suppose that depends on the ham. Most are in the FCC database with their home addresses, although some use PO Boxes. No need for direction finding tools when you can just look them up by call sign. But it will be interesting to see if certain politically oriented pirates keep up their transmissions. I suppose that they'd have little to worry about if they regularly go out in the field to do their thing, but those transmitting from home (even the ones who just play music and don't have content that would offend anyone) might have to worry. A lot of hams HATE pirates.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: ChrisSmolinski on July 14, 2018, 2349 UTC
With an accuracy of 50 or so miles, or even 25 if you are lucky, this technique is not going to identify a particular operator's address. The best you will do is get the major city / metro area.   So you do this to a particular station and end up with say the Chicago metro area. That narrows it down to a few million people  ;D

If you're in the hobby and know the players, I suppose you could narrow things down a it, or use it to confirm or deny your guess as to who is running a particular station. Or figure out which stations are run by the same operator. Of course, you could do all of this before by looking at signal characteristics, both propagation and other technical "tells" that each operator has. The Kiwi TDoA makes this a little easier and more automated now.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Josh on July 15, 2018, 1940 UTC
I hope this morphs into a game, see who gets closest to the transmitter.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: ChrisSmolinski on July 15, 2018, 2023 UTC
I remembered how "back in the day" it was common for pirates to be relayed by other stations (no doubt by mailing cassette tapes), without any on the air notice that it was a relay. This allowed listeners in other areas to hear the station, and probably caused at least a little confusion at the agencies. We might see operators doing the same thing today (well, minus the cassette tape part), if WXYZ is transmitted from half a dozen locations, no one would know which, if any, was the operator's location.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: redhat on July 15, 2018, 2046 UTC
Plus today we have streaming, so you can run a live show from the other side of the planet if need be.

+-RH
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: BoomboxDX on July 16, 2018, 1152 UTC
How does this work when there are more than one station on a frequency?

Like, since hams have been mentioned here, could they use this to pinpoint the guys who play music and cuss a lot?

Because those frequencies have other transmissions going on simultaneously.

Does this feature only work when there is a sole signal on a frequency?

Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Token on July 16, 2018, 1309 UTC
How does this work when there are more than one station on a frequency?

Like, since hams have been mentioned here, could they use this to pinpoint the guys who play music and cuss a lot?

Because those frequencies have other transmissions going on simultaneously.

Does this feature only work when there is a sole signal on a frequency?

I have not taken the Kiwi TDOA code apart, so let me start by saying that what I am about to say is supposition, based on an understanding of the basic techniques and what I have observed from the system.  I could be out to lunch on some details, but I think I probably am correct on the major points.

I suspect anytime two separately transmitted sources of audio are in the same passband it will mess with the software, reducing the quality of the plots, but the below is a more sterile description, assuming worst case.

The system starts by taking simultaneous ~30 second samples from your selected SDRs.  You typically select SDRs that have the signal you are interested in as strong as possible.  You manually, one at a time, check the signal on each SDR to determine which SDR will be on your "list" of sampling machines.  Ideally you will have at least 3, and as many as 6, machines in your list.  Less than 3 will result in a curve, but not an intersection.

The software then runs all the samples you have taken to find identifiable features, something unique in the audio that the software can identify in all the samples.

After finding this (or these, I don't know how many it does per sample, but I assume it tries to find more than one) unique features it establishes the time of arrival at each SDR for the selected features.  It then plots the curves for each pair of receivers, calculates the intersection points and sigmas, and puts them on the map.

If the software attempts to find a single unique feature, and if there are two or more signals on the frequency, and you have selected receivers where the desired signal is strong and the second signal is weak, it is likely it will still find a unique feature for one of the stations.  In which case it will still plot only one transmitter.  Which one it plots is anyone's guess.

If the software attempts to find multiple features and time each of them, then it is less likely to plot only a single transmitter, but rather might indeed plot combinations of both transmitters, resulting in junk.

Regardless of how it does it though, if you had two widely separated stations on SSB simulcasting the same program (SSB so no destructive interference, AGC capture, or jamming, at worst a bit of an echo on the signal), with the same audio at the same time (not just two stations running the same tapes at the same time, but actual simulcast of the same audio stream) it would find corresponding features in each, and that would probably ruin the calculations.  The software might still plot something, but it would probably be junk, combinations of the curves for the two stations.  If each curve is nice and tight (good signal quality and good, tight, features to ID) it may calculate curves on the wrong time deltas, show curves and intersections in totally wrong areas.

Again, the above is based on some assumptions.

Could it be used to find the ham jammers?  Maybe, but remember what I said about the 30 second samples.  Transmissions from multiple stations, even if one at a time, that have handoff times inside that 30 second window will likely mess with the system.  So if the jammer does not stay on the air for the entire sample time that will probably result in errors, jumbled combinations of the data for the jammer and jammed stations.

T!
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: KaySeeks on July 16, 2018, 1729 UTC
If the software attempts to find multiple features and time each of them, then it is less likely to plot only a single transmitter, but rather might indeed plot combinations of both transmitters, resulting in junk.

In fact, I was wondering about exactly this so I attempted to "find" WWV on 5 MHz, 10 MHz and 15 MHz with receivers on the west coast of North America in the presence of WWVH (and passband narrowed to ~100-200 Hz so that differences in the male voice on WWV and the female voice on WWVH were reduced and the focus was on the carriers only). I don't have the results available right now but let's just say that things became "confused". It seems to me that as a general principle with TDoA, anytime there is a significant amount of skywave propagation present, the derived result varies quite a bit over time (see more on this at the bottom of this post). In this case, this was worse than I expected. I suspect (but was not able to prove beyond a doubt) that the presence of WWVH confused the algorithm.

Could it be used to find the ham jammers?  Maybe, but remember what I said about the 30 second samples.  Transmissions from multiple stations, even if one at a time, that have handoff times inside that 30 second window will likely mess with the system.  So if the jammer does not stay on the air for the entire sample time that will probably result in errors, jumbled combinations of the data for the jammer and jammed stations.

There has been some discussion about allowing for sampling intervals shorter than 30 seconds for reasons like this.

Getting back to what I mentioned before, skywave propagation is a big confounder here - it will cause a fair amount of variation from location attempt to location attempt. (This makes sense to me as the ionosphere will produce significant variable amplitude and phase shifts when the signal returns to earth.) Also, weak signals are more difficult to get a clean result on. Contrast this with strong, groundwave signals, which are relatively easy to locate. I was able to locate BBC - Droitwich (198 KHz) and RTL (234 KHz) to within ~10 km using only 3 receivers and I was able to repeat both using a second completely different group of receivers as a check. I did the same with WWV on 2500 KHz (only one set of three receivers though). However, 5, 10 and 15 MHz are not trivial and derived location was highly variable. I assume that this is due to the significant skywave propagation there.

All this means that HF pirates probably have little to worry about by the Kiwi TDoA network. You are quite unlikely to be successfully located down to your house. (I can't comment on what the authorities might be able to do though, so beware.) A MW or LW pirate might want to pay attention though.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: ChrisSmolinski on July 16, 2018, 1802 UTC
All this means that HF pirates probably have little to worry about by the Kiwi TDoA network. You are quite unlikely to be successfully located down to your house. (I can't comment on what the authorities might be able to do though, so beware.) A MW or LW pirate might want to pay attention though.

Exactly. 50 or even 25 miles of accuracy (typical with skywave HF signals) is not going to uniquely identify anyone.  Some operators dislike the fact that now their general location (Chicago vs Boston for example) will be known, however. There's no changing that now. And to be honest, that's been possible previously without TDoA.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Josh on July 16, 2018, 1815 UTC
If the kiwis would employ vertical antennas, it would help the tdoa work with regards to skywave.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: KaySeeks on July 16, 2018, 1822 UTC
50 or even 25 miles of accuracy (typical with skywave HF signals) is not going to uniquely identify anyone. 
You are doing well if you can repeatably locate an HF signal that isn't from some 10+ kW transmitter to within those distance ranges. I haven't been able to do that well generally. That Link11 signal on ~6942 KHz we have been talking about in that other thread is an exception and is a very strong signal.

Some operators dislike the fact that now their general location (Chicago vs Boston for example) will be known, however. There's no changing that now. And to be honest, that's been possible previously without TDoA.
Right. For example, ways of doing this include: 1) looking at propagation characteristics and also 2) sniffing around with the many receivers on the internet.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: KaySeeks on July 16, 2018, 1823 UTC
If the kiwis would employ vertical antennas, it would help the tdoa work with regards to skywave.

If the pirates employed more NVIS, it would make it more difficult too.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Brian on July 16, 2018, 1932 UTC
All this means that HF pirates probably have little to worry about by the Kiwi TDoA network. You are quite unlikely to be successfully located down to your house. (I can't comment on what the authorities might be able to do though, so beware.) A MW or LW pirate might want to pay attention though.

Exactly. 50 or even 25 miles of accuracy (typical with skywave HF signals) is not going to uniquely identify anyone.  Some operators dislike the fact that now their general location (Chicago vs Boston for example) will be known, however. There's no changing that now. And to be honest, that's been possible previously without TDoA.

The monitoring stations here in Europe land are pretty good at DFing HF signals. They have me down to about 10 or 12 miles and another station possibly even closer than that. That's within groundwave, if they really wanted to nail me, they could.

They don't always get it right though. They think another station is VERY close to my location. I'ts actually about 80/90 miles away.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Token on July 17, 2018, 0029 UTC
Getting back to what I mentioned before, skywave propagation is a big confounder here - it will cause a fair amount of variation from location attempt to location attempt. (This makes sense to me as the ionosphere will produce significant variable amplitude and phase shifts when the signal returns to earth.) Also, weak signals are more difficult to get a clean result on. Contrast this with strong, groundwave signals, which are relatively easy to locate. I was able to locate BBC - Droitwich (198 KHz) and RTL (234 KHz) to within ~10 km using only 3 receivers and I was able to repeat both using a second completely different group of receivers as a check. I did the same with WWV on 2500 KHz (only one set of three receivers though). However, 5, 10 and 15 MHz are not trivial and derived location was highly variable. I assume that this is due to the significant skywave propagation there.

All this means that HF pirates probably have little to worry about by the Kiwi TDoA network. You are quite unlikely to be successfully located down to your house. (I can't comment on what the authorities might be able to do though, so beware.) A MW or LW pirate might want to pay attention though.

Those really accurate plots of signals in Europe tend to be with all the RX locations in groundwave, and working with very good SNR.  On the other hand, I have plotted WWV to within 9 km on 15 MHz, using 3 RXs located more than 1000 miles away.

Skywave itself is not a problem to TDOA.  It is variations in the number of hops and altitude of reflective layers to each of the receive stations.

Basically if all of the receive stations are roughly the same distance from the target then the increased distance (and so time) caused by skywave vs direct path will be approximately the same for all the receive stations.  In other words, despite the fact each receive location will get the signal a little later than ground wave, they will all have roughly the same skywave induced delta T, and it will be factored out in the calculations.

The inaccuracies start to get larger as you have receive stations of widely varying distances from the target.  A worst case would be say one receiver in ground wave and another in double or triple hop.  This would skew the resultant curve between those two stations by the skywave delta T and away from the ground wave station.  Even if the third receive station is in double or triple hop skywave only one curve will be accurate, the curve between the two skywave receive stations.  So two of the three resultant curves (A vs B, A vs C, and B vs C) will have significant errors, and the intersection of all three curves (the plotted position) will be shifted a good bit.

I have modeled plots with one RX in groundwave and the other two in high double hop skywave, and moved the resulting mapped TX location by greater than 200 km.  Just because it is a nice, tight, plot does not make it right ;)

So, good signal strength (good SNR) and all receive locations evenly distributed around the target and roughly the same distance from the target can yield very good results, skywave or not.  This is particularly true if all the receive locations are in say daylight, or all are in night, vs some in daylight and some in night.

T!
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: John Poet on July 17, 2018, 0100 UTC

While some of us have been posting DF maps of broadcast and utility stations, I expect that all users understand that it would be best to refrain from posting any maps of pirate stations.


Why not make that a RULE for this forum, Chris?  NO POSTING DF MAPS OF PIRATE STATIONS! (or other location information, for that matter).
There are certainly enough moderators to make it stick and quickly remove any such thing...

It would probably make a lot of the ops feel better.  What's worse than individual listeners being able to do this DFing, is if that information would become published or widely disseminated.  This would surely result in a reduction in stations and broadcasts...
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: ChrisSmolinski on July 17, 2018, 1541 UTC

While some of us have been posting DF maps of broadcast and utility stations, I expect that all users understand that it would be best to refrain from posting any maps of pirate stations.


Why not make that a RULE for this forum, Chris?  NO POSTING DF MAPS OF PIRATE STATIONS! (or other location information, for that matter).
There are certainly enough moderators to make it stick and quickly remove any such thing...

It would probably make a lot of the ops feel better.  What's worse than individual listeners being able to do this DFing, is if that information would become published or widely disseminated.  This would surely result in a reduction in stations and broadcasts...

We can make it even slightly more broad than that, no DOXing of anyone, operator or listener. This would include TDoA maps, real names, locations, etc. Both posting the information here, as well as links to such information on other sites.   Reasonable?
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: TheRelayStation on July 17, 2018, 1630 UTC

While some of us have been posting DF maps of broadcast and utility stations, I expect that all users understand that it would be best to refrain from posting any maps of pirate stations.


Why not make that a RULE for this forum, Chris?  NO POSTING DF MAPS OF PIRATE STATIONS! (or other location information, for that matter).
There are certainly enough moderators to make it stick and quickly remove any such thing...

It would probably make a lot of the ops feel better.  What's worse than individual listeners being able to do this DFing, is if that information would become published or widely disseminated.  This would surely result in a reduction in stations and broadcasts...

We can make it even slightly more broad than that, no DOXing of anyone, operator or listener. This would include TDoA maps, real names, locations, etc. Both posting the information here, as well as links to such information on other sites.   Reasonable?
i agree and yes, that is very reasonable.
please apply this rule to the chat as well as the forum.
i would have these warnings posted as a sticky for all forum topics as well as for new members who register, they would have to read it and accept the terms before they can continue.
all moderators should be notified of the changes and immediately remove any content that reveals the location and other personal info of an OP or Hobbyist.
repeat offenders should be banned depending on how many times they infringe the rules (my opinion).
this is an excellent forum and hobby and although i do not mind that my location may be known, its better that everyone keeps that info to themselves since there is really nothing i can do to avert it from becoming known anyway (experienced individuals could easily obtain location info before TDoA on Kiwi, TDoA just made it easier for the average person).
hopefully, those who do know sensitive information about OP's do not spread it around using other means such as social media.
just about every HFU member is a respectable adult that knows better, so i dont expect any problems to surface as a result of TDoA on Kiwi though it is good practice to cover those bases.

Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Oliver on July 17, 2018, 1720 UTC
I fully agree with the statements of JP,   Chris & The Relay Station.
Those should be in my opinion the rules of the game for every board member.
It would be counterproductive to our hobby, to use new technologys and spreading the gained information with the possibility to harm any of the operators outhere who make this hobby so enjoyable.

One last thought, would it be possible to come to a similar agreement with the moderators of Iann's Chat?
I assume that some of you have a thigther relationship with some of the moderators on chat to discuss this topic.

Thanks,
Oliver
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: John Poet on July 17, 2018, 1908 UTC

While some of us have been posting DF maps of broadcast and utility stations, I expect that all users understand that it would be best to refrain from posting any maps of pirate stations.


Why not make that a RULE for this forum, Chris?  NO POSTING DF MAPS OF PIRATE STATIONS! (or other location information, for that matter).
There are certainly enough moderators to make it stick and quickly remove any such thing...

It would probably make a lot of the ops feel better.  What's worse than individual listeners being able to do this DFing, is if that information would become published or widely disseminated.  This would surely result in a reduction in stations and broadcasts...

We can make it even slightly more broad than that, no DOXing of anyone, operator or listener. This would include TDoA maps, real names, locations, etc. Both posting the information here, as well as links to such information on other sites.   Reasonable?

YES!   Absolutely.

Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Josh on July 17, 2018, 2147 UTC
If the kiwis would employ vertical antennas, it would help the tdoa work with regards to skywave.

If the pirates employed more NVIS, it would make it more difficult too.

Yeah, nvis done right will result in a df fix straight up.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: ChrisSmolinski on July 17, 2018, 2151 UTC
Yeah, nvis done right will result in a df fix straight up.

Not necessarily with TdoA. The height of the ionosphere can be taken into account.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Azimuth Coordinator on July 17, 2018, 2200 UTC
My take is.  I'm not comfortable about the technology.   
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: ION Radio on July 17, 2018, 2251 UTC
My take is.  I'm not comfortable about the technology.

I'm not comfy with this at all myself AC. It just seems too easy.     :o
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: ChrisSmolinski on July 18, 2018, 0015 UTC
The bad news is listeners can sometimes find out where a station is located within 50 miles or so... if everything works.

The good news is listeners can sometimes get a completely wrong result (for example, I tried some SWBC stations and it was off by a few hundred miles some times), and not know the result is wrong.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Token on July 18, 2018, 0241 UTC
Yeah, nvis done right will result in a df fix straight up.

The direction and angle of arrival might well be up at a high angle, however TDOA does not use angle cuts to plot position.  So TDOA can arrive at accurate position fixes despite high angles.

The good news is that while TDOA CAN arrive at very good positional fixes, it can also plot positions way far from reality that look great.  And the user, especially the average, uninformed user, may never know the difference.

T!
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: Monophonia on July 24, 2018, 1344 UTC

The good news is that while TDOA CAN arrive at very good positional fixes, it can also plot positions way far from reality that look great.  And the user, especially the average, uninformed user, may never know the difference.


Yep, Like the first time I attempted a DF test right when the feature launched. It "found" WRMI very firmly in North Carolina.
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: ChrisSmolinski on July 24, 2018, 1421 UTC

The good news is that while TDOA CAN arrive at very good positional fixes, it can also plot positions way far from reality that look great.  And the user, especially the average, uninformed user, may never know the difference.


Yep, Like the first time I attempted a DF test right when the feature launched. It "found" WRMI very firmly in North Carolina.

Kiwi TDoA works extremely well if you already know where the transmitter is located, so you can filter out bogus results  ;D
Title: Re: Kiwi TDoA Direction Finding Increases SW Pirate Institutional Paranoia Levels
Post by: KaySeeks on July 25, 2018, 0021 UTC
So, good signal strength (good SNR) and all receive locations evenly distributed around the target and roughly the same distance from the target can yield very good results, skywave or not. 

Yes, in fact back around the time that you wrote this, I realized that I had gravitated toward an understanding that one RX being much closer or farther away than the others would skew the results. I had more-or-less come to a belief of exactly what you say here - equidistant RXs are optimal - through trial and error.

Of course, this is more complicated if you don't know where the TX is (which is the point of the whole exercise). You use an iterative process to narrow it down. However, even with this knowledge, things can and will go wrong.

Because of my belief in "robust" solutions to things, I like to attempt to achieve basically the same location result with a mostly or completely different set of RXs. If it's a correct solution, I believe that you should achieve a corroborating result. If the RXs are roughly equidistant, I have been able to achieve a similar result this way, which is reassuring.

Sometimes I try to test it to be sure that it is leading me to the right solution by picking RXs that are not centered on the previous result, perhaps not surrounded by the RXs at all. The hope is that it at least tells me that the TX location is somewhere off in the direction of the previous result, i.e., corroborating. Unfortunately, this works maybe 50% of the time. The other 50% of the time, I get a completely different outcome that is also equidistant from those RXs in use for that second run, nowhere near the previous result and not a result that says “No, no. You are headed in the wrong direction.”

If you think about the implications of this, that is what makes the process of using TDoA on an unknown TX very difficult. It is very easy to be lead astray.