[time-nuts] GPS for ntp

[Joseph Gray]

What does everyone think of this GPS module for ntp use? According to the
specsheet, it uses a Ublox Neo-7N.

http://www.ebay.com/itm/RY725AI-10Hz-UART-USB-interface-GPS-Glonass-QZSS-antenna-module-flash-memory-/181562403752

I'm thinking about using it for a Beaglebone ntp server. I know there was
some discussion about Beaglebones a while back. Has anyone gotten ntpd with
PPS and time stamping running on a Beaglebone yet (like on the Soekris
Net4501)?

Does anyone want to take a wild guess as to the best/worst case UTC offset
I might get with such a setup? I realize that I'd have to try it to really
find out, but guesses and advice from those more knowledgeable is always
appreciated.

What I'm really after is to eventually have several Beaglebones scattered
around the area as part of a TDOA DF network. I have spare radios to
dedicate to the task. Each fixed node will timestamp incoming transmissions
and then relay that information to a central location. The central system
will use the data to calculate the location of the transmitter.

Does anyone here have any experience with this sort of thing? Would you
recommend a better way of accurately timing the transmissions vs using ntp
on each Beaglebone?

I know that TDOA is used by the cellular companies. Is anyone aware of some
"user level" projects or source code for this? I've Googled a bit, but
haven't turned up much. There was one thesis about an Amateur doing part of
this, but he didn't have much detail on the satellite nodes and didn't
describe anything about the centralized processing part.

I have one Beaglebone White that I got cheap, so I have something to get
started with. Later, as I figure out things, I'll buy a few Beaglebone
Blacks.

Joe Gray
W5JG