[time-nuts] anyone tried the cheap Lea-6T modules seen on eBay?

[Dale J. Robertson]

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: EWKehren at aol.com ; time-nuts at 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 at 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.cook at 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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