#datatrak — Public Fediverse posts

Oh damn, there WAS a #Datatrak TX station in Filey. Looks like it stuck around until between 2011 and 2018. By July 2018 it had been completely scrubbed from the landscape and replaced with a wind farm.

I can't overstate how rare it is for one to be completely scrubbed from the landscape like this. More commonly the masts are pulled down and the concrete pad remains. More commonly still, they're left until they fall down.

Fun fact: the ethereal #Datatrak sound even got into a short film. "145 kHz" by Ian Bell and Julia Childs at Another Wave AV Productions.

https://www.youtube.com/watch?v=krF8f1Ic690

https://collections-search.bfi.org.uk/web/Details/ChoiceFilmWorks/150736624

I think the thing I'm most chuffed about with all the #Datatrak stuff isn't the reverse engineering. It's that I added "wav file output" as an option and one of the people who helped build the system now has it as his phone ringtone.

I'm not far off doing that myself... after some filtering it has a sort of ethereal air about it. To the point someone made a film, "145 kHz", about it.

I won't say why I'm using Eastnor Deer Park as a test location, but also please don't tell Jonty. #datatrak

This is what the old Datatrak UK network looks like in field strength, WHDOP, repeatable accuracy and measurement confidence factor.
These seem to match up pretty closely with Williams (2004).
If you want to play with it, it's on Github:
https://github.com/philpem/datatrak-bandpass2

Tip: Set the Grid Resolution to about 10km per square to start with for fast calculation, then reduce it for prettier plots.
#Datatrak

If anyone else is interested in the #Datatrak LF navigation network, it turns out Alwyn Williams' PhD thesis is on the University of Bangor's website for download:
https://research.bangor.ac.uk/en/studentTheses/prediction-of-the-coverage-and-performance-of-the-datatrak-low-fr/

This contains a mountain of information on the network and how it was set up. It's a long read though - 300 pages.

macOS and Linux autobuilds 95% pass rate. Takes under a minute (each) to run.
Windows autobuild? 45%. Takes 20 minutes to run.

I'm on the verge of disabling the Windows autobuild and saying "screw that platform".

(this is related to my trying to put together a #Datatrak network simulator and foolishly answering "which platform?" with "yes")

Doing work while I occasionally watch my poor Thinkpad running number crunching to undo the effect of an IIR filter by brute force and ignorance.
#datatrak things.

Anyone wanting to make a hokey #Datatrak transmitter in the 1980s/90s would have had a job on. The phase values go through an IIR filter on their way to the trigger (sync marker) template matcher.
If you use the trigger templates from the firmware, it only matches on '1' bits. If you use a sine wave it won't match at all.
I'm using simulated annealing and a model of the receiver software to try and improve the trigger waveforms...

great, now I have an #EMFcamp project crisis: do I do the cable TV, or do I try and talk some people into putting up big masts and bringing back #Datatrak for one weekend only?

Spent a bit of time looking at #Datatrak again last night. The upshot is, now I know how the almanac, Fast Update Table (almanac updates) and vehicle commands are sent.
It's not fast. One byte every 1.68 seconds, muxed into three streams. About 108 seconds to send a packet (command) on all three streams.

Doing some more #Datatrak reverse engineering now I've got the navigation signal working. There are three things I want to figure out:
* Vehicle data
* The Almanac data loop
* The Fast Update Table (a shorter almanac loop which only carries recent updates)

Logically I should start at the MSIR (millisecond interrupt) and follow the breadcrumb trail down into the task scheduler but there's a quicker way (1/n)

Today I've been working on #Datatrak. I think this is the first time in ten years that this signal has been heard.

@HopelessDemigod hihi! I'm trying to get into LF is probably a better way to put it, but I reverse engineered a radio navigation receiver (see my #datatrak posts) and wanted to retune it to the ham band and build a transmitter. Problem is I'd need two to prove the concept and three to make it work.

Been given a box of spare ROMs, allegedly found in a pile of #Datatrak gear that turned up on ebay some time ago.
After matching up the images, I found what appears to be LFTX v8.1.1.8 - the LF transmitter software.

Sadly it doesn't boot in the Locator emulator. Digging further, the rackmount hardware was a Force Computers 68000 VME-Bus system, and the unknown writes are to mystery VME cards.
Wish I knew the first thing about #VMEbus...

Been given a box of spare ROMs, allegedly found in a pile of #Datatrak gear that turned up on ebay some time ago.
After matching up the images, I found what appears to be LFTX v8.1.1.8 - the LF transmitter software.

Sadly it doesn't boot in the Locator emulator. Digging further, the rackmount hardware was a Force Computers 68000 VME-Bus system, and the unknown writes are to mystery VME cards.
Wish I knew the first thing about #VMEbus...

Been given a box of spare ROMs, allegedly found in a pile of #Datatrak gear that turned up on ebay some time ago.
After matching up the images, I found what appears to be LFTX v8.1.1.8 - the LF transmitter software.

Sadly it doesn't boot in the Locator emulator. Digging further, the rackmount hardware was a Force Computers 68000 VME-Bus system, and the unknown writes are to mystery VME cards.
Wish I knew the first thing about #VMEbus...

Been given a box of spare ROMs, allegedly found in a pile of #Datatrak gear that turned up on ebay some time ago.
After matching up the images, I found what appears to be LFTX v8.1.1.8 - the LF transmitter software.

Sadly it doesn't boot in the Locator emulator. Digging further, the rackmount hardware was a Force Computers 68000 VME-Bus system, and the unknown writes are to mystery VME cards.
Wish I knew the first thing about #VMEbus...

Been given a box of spare ROMs, allegedly found in a pile of #Datatrak gear that turned up on ebay some time ago.
After matching up the images, I found what appears to be LFTX v8.1.1.8 - the LF transmitter software.

Sadly it doesn't boot in the Locator emulator. Digging further, the rackmount hardware was a Force Computers 68000 VME-Bus system, and the unknown writes are to mystery VME cards.
Wish I knew the first thing about #VMEbus...

#Datatrak teaser: a sales leaflet from the early days. You can tell it's early because it shows Securicor and Wimpey/Wimpol's involvement. Later on Wimpey stepped back and handed the reins to Securicor.

The Locator in the photo is the Mk1, the original 68008 based unit.

edit: I love the little photo of the #DEC hardware - an RA81 hard drive and something else on top of it.

"How would you like a pile of #Datatrak stuff? I found it in our store cupboard and saw your website on Google when I tried to find out about it."

It's going to take ages to dig through these boxes of old hardware.