[ltp] Mounting a Sierra Wireless EM7345 in a Thinkpad X301

[Bjørn Mork]

I don't recommend this exercise.  It's unnecessarily complicated to use
an m.2 (aka NGFF) modem in an older laptop instead of a readily
available mini-PCIe alternative. And the BIOS problems are exactly the
same. I did use an original Lenovo part here, but it is just as
unsupported in this laptop as anything else.

But in case anyone is interested, this is a description of how I put an
EM7345 in my X301. Added some pictures to the description of the MC7710
mounting: http://www.mork.no/~bjorn/thinkpad-lte/

The real problem with an m.2 module is that it uses smaller antenna
contacts called I-PEX MHF4 (there is a compatible Hirose variant too,
but I don't know it's name). m.2 to mini-PCIe adapters are readily
available, but I couldn't find any suitable antenna cable converters.
The best I could find was MHF4 to SMA pigtails, which could then be
combined with SMA to U.FL test plugs. So I ordered a few of each before
actually thinking about where anything as big as an SMA connector could
fit inside an X301.  It does of course not. The diameter of an SMA plug
is actually larger than the thinkness of the X301 DVD burner.

So I ended up cutting off the SMA connector on two of the pigtails and
soldering on surface mount U.FL contacts instead, creating a sort of
female U.FL to male MHF4 pigtail.  Because I am no good at soldering,
and I don't think the surface mount U.FL contacts soldered to a .8 mm
think coax cable would survive the strain caused by connecting and
disconnecting the antenna, I glued these pigtails to the m.2 adapter.
The idea is that the glue helps support the soldered end and takes care
of most of the force applied to the U.FL contact when disconnecting a
cable from it.

This worked pretty well.  The result is a module about the same size as
a full size mini-PCIe modem, complete with U.FL contacts.

I haven't done any sort of measurement on the antenna connections.  I do
expect them to be sub-optimal.  But at least it works.  I get about the
same LTE performance as I did with the MC7710.

My purpose with this?  I wanted to test an EM7345 myself, but I'm not
prepared to give up my X301 :-)


Bjørn