They use the LEA-6T for DIY drone applications because it provides raw
carrier phase information. The raw carrier info is compared with the raw
carrier data from a nearby fixed (and surveyed for an extended period) GPS
receiver. The position error of the fixed station is subtracted from the
reported position of the 'roamer' , the resultant position is supposed to be
accurate to within 10cm of true position. All this is done via a suite of
open source applications called RTKLib. ublox was the only relatively
inexpensive gps module that provided the phase data needed to make all this
work. More recently a few of the other module vendors including skytraq
(sp?) have provided this function. Getting a module that provided carrier
data for less than $100 US was a big deal for the drone community. The only
other cheap module that I know about is the synergy ssr-6t which works very
well but (very minor nit) has a small pitch connector that was a nuisance to
make the interconnects for. These chinese modules look to be much easier to
interface. I'll probably buy one eventually just to see if the deviations
from the pcb design rec's have impacted the performance in my application.
Regards,
Dale NV8U
-----Original Message-----
From: S. Jackson via time-nuts
Sent: Tuesday, November 25, 2014 2:41 PM
To: ewkeh...@aol.com ; time-nuts@febo.com
Subject: Re: [time-nuts] anyone tried the cheap Lea-6T modules seen on eBay?
Bert,
the LEA-6T actually has software bugs that show up in moving applications
and that need to be handled by the users' software, and they are selling it
for drone applications. Without any monitoring for these bugs the units
may really only be useful for stationary applications.
Why they would choose the 6T unit instead of a non-T unit at half the price
would only be because they got those as surplus really cheap I would
think.
bye,
Said
In a message dated 11/25/2014 09:50:12 Pacific Standard Time,
time-nuts@febo.com writes:
A Lea-6T is only worth any extra money if you are using the sawtooth
correction data coming out of it. With out correction a $ 14 unit is just
as
good.
Bert Kehren
In a message dated 11/25/2014 11:25:34 A.M. Eastern Standard Time,
michael.c...@sfr.fr writes:
You may have seen them as in
<http://www.ebay.fr/itm/Ublox-LEA-6T-GPS-Module-w-Compass-for-APM2-5-APM2-6-
Flight-Controller-Multirotor-/271641375221?pt=UK_ToysGames_RadioControlled_J
N&hash=item3f3f1671f5>
There are other sellers with the same.
My idea was to see if one was suitable as a 1PPS locking source for my
PRS10. The interest for me being that it powers directly from a USB
connection
and can be configured with the Ublox’s u-center software, so
implementation is a no brainer.
All I needed to do was to replace the patch antenna with an SMA-F
connector and add a wire for the 1PPS. Despite having less than ideal
antenna
position, once the survey was complete I was getting +/-20ns jitter on
the 1PPS
which is within spec and stable over the day.
However I was most disappointed to see that the 1PPS output voltage is
only 2.16 +/-0.4V. According to spec it should be Vcc+/-0.4V and I have
Vcc
measuring 3.3V. I can’t see the board trace but the measured voltage is
the
same on the PPS pad next to the JST-SH connector and on the GPS modules
pin
28 so it is not a board issue. Unfortunately this is too low to tickle
the
PRS10 1PPS input. I guess I could add a buffer or AND gate to fix it, but
that sort of defeats the object and introduces extra jitter and offset.
It is however enough for a Raspberry-Pi GPIO input, so I have relegated
it
to NTP PPS.
Has anyone out there got one of these and seen the same symptoms? Or
maybe
you have one and it is OK? I’d like to know.
You will be able to see from the eBay photos that this a 6T-0-000 version
which is an early version and it could be that they are cheap as some/all
have this defect. So beware.
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