[time-nuts] Ebay Huawei Ublox M8T Modules Warning

[Matthias Welwarsky]

On Samstag, 9. Januar 2021 23:38:35 CET Nigel gm8pzr via time-nuts wrote:
> I've dealt with this seller before, always been very happy with the results,
> and agreed a price on three such modules which arrived just before
> Christmas, for reference this particular Ebay ID was 333619130232, and
> finally found time to start checking them today. The modules themselves
> look very nice, but one of the auction photos is a connection diagram that
> shows Pin 2 of the 8 pin interface connector as "Power In 5V DC", and on
> this PCB that pin connects directly to the pin 6 Vcc input on the Ublox
> module, which has an absolute maximum rating of 3.6V .......whoops! This is
> not intended in any way to be a criticism of this seller, who I am more
> than happy to recommend, nor indeed of any other seller, but this is a
> generic diagram that several sellers are using for various Huawei/Ublox
> modules, some of which may have an onboard 3.3V regulator, as presumably
> did the one this diagram originally referenced, but some of which may not.

On a cursory look at the PCB, there are more odd details about it. The antenna 
circuitry and especially the bias-t looks wrong. The connection diagram lists 
a 5V pin for an antenna voltage supply and there seems to be a dedicated 
circuit for short/open circuit detection, but there's no DC blocking cap in 
the antenna feed line.

I'm starting to believe that this board was not originally designed for a LEA-
M8 at all. In fact it was probably made for a LEA-6T, the open/short antenna 
detection looks a bit like the circuit shown in figure 47 in the LEA-6 HIM. 
Also, the LEA-6 modules have an internal DC block in the antenna input so you 
would not need an external one.

Regards,
Matthias