You've probably been playing around with the huge KiwiSDR network which can be reached from http://sdr.hu/ . Just this week, too late to put into the column, it has rolled out a new beta with a recorder and a Time Difference of Arrivial (TDoA) direction finder.
Both seem pretty slick. The recorder is self-explanatory. You click a big red button over on the top right of the control panel, and it starts recording. Click again, and it stops, at which point it downloads to your computer. This will save me having to remember to start a recording application on this computer every time sometime gets interesting. Also, it's possible the recording will be minus whatever net dropouts and errors you get in transit to your machine. I'm not sure yet, but it sounds logical.
The TDoA has a learning curve. When I get it to work, I'll write more about it. Basically, it uses the KiwiSDR network as one huge direction finding system, synchronized to GPS time and positions. The user tunes in a station to locate, changes the mode to "IQ" (In phase/Quadrature) and selects other SDRs positioned to receive the signal and give a good solid computation. That's the tricky part. Ground wave signals work best, favoring the VLF/LF stations. Also sometimes enough receivers can be found near the target. One can make sure the other SDRs receive the signal too by double-clicking them, which opens them in a new tab.
When it's all set up, click "select" and watch it churn. It can go for several minutes. I have yet to have it return a "heat map" with the most likely positions, but others have. For example, someone got a pretty good fix on the 4625 kHz Russian "buzzer" ("UVB-76," S38). The hot spot shown is outside St. Petersburg. In other words, right where I told you it was.
More on the TDoA here.
This could have a major effect on the hobby. More information as it comes.
