Recalibration, band conversion and bug #1024 rework

Mychaela Falconia mychaela.falconia at
Wed Feb 14 22:40:01 UTC 2018

Hello OM community,

I am pleased to announce that my company Falconia Partners LLC is now
offering GSM RF tract recalibration services for Openmoko's Neo 1973
and Neo FreeRunner devices.  Like all other commercial GSM phones and
modems, these smartphones had their GSM RF parameters individually
calibrated on the factory production line.  This factory calibration
normally persists for the lifetime of the device, but because the
calibration values are stored in the Calypso modem's flash file
system, it is possible that some Neo owners may have lost theirs as a
result of careless playing with modem flashing tools.  The latter
scenario is quite likely to have happened in the bad old days before
FreeCalypso when the modem was treated as some kind of "thou shalt not
enter" forbidden zone, and the modem flashing tools and documentation
were available only in a hush-hush, whisper-whisper manner.  GSM RF
calibration also needs to be redone if the RF hardware has been
physically modified in any way, e.g., to convert a 900 MHz device to
850 MHz or vice-versa.

Because my company produces new Calypso GSM modems that are very
similar to Openmoko's, we have the necessary facilities to perform our
own RF calibration that is no worse than what OM's factory did.  The
RF test instrument that is used to perform the calibration is a
Rohde&Schwarz CMU200, and this instrument itself needs to be kept in
good calibration standing - the chain of traceability goes back to
national standards labs like NIST.  Our CMU200 instrument has just
been calibrated by Rohde&Schwarz in Maryland; here is the official
calibration certificate:

In addition to the measuring instrument, the process of calibrating
the RF tract on a Calypso GSM device involves special software that
talks both to the firmware running on the Calypso (which naturally
needs to be TI-based) and to the CMU200 or other external RF test
equipment.  The original software that was used by OM's factory
appears to have been lost, hence an entirely new replacement had to be
developed from scratch here at Falconia Partners LLC, based on the
available bits of documentation from TI and meticulous reverse
engineering.  Our new calibration software is freely published, so you
can see exactly what we do when we calibrate a Calypso GSM device:

If anyone has a GTA02 or GTA01 device that needs to be recalibrated or
could benefit from such, you can send it to Falconia Partners LLC to
be serviced.  As long as the demand is low, there will be no charge
for the recalibration service other than return shipping.  If you are
going to sending your device in for service, please take the battery
out, i.e., send the device WITHOUT the battery.  Postal services have
become very uptight about lithium batteries recently, hence the return
shipping will cost a lot more if I have to deal with the extra
bureaucratic hurdles of shipping the device back to you with that
Li-ion battery in it.

The calibration service is completely non-invasive, i.e., your device
won't need to be disassembled beyond taking the back cover off.  Your
Neo will have 3 cables plugged into it (USB for talking to U-Boot,
another USB-serial cable in the headset jack for talking to the
Calypso, and an RF test cable going to the CMU200 inserted into the RF
test port under the back cover), the application processor will be
booted into NOR U-Boot, the latter will be used to execute neo gsm on
and neo gsm off commands via USB, and the headset jack serial port
will be used to operate on the Calypso modem.  Whatever software you
are running on the phone's application processor will be left
completely untouched.

If there is interest, my company may also be able to offer a band
conversion service, i.e., converting a 900 MHz FreeRunner to 850 MHz
or vice-versa.  To make such conversion, one SAW filter part in the
GSM section of the motherboard needs to be changed (populate Epcos
B7820 for 900 MHz or B7845 for 850 MHz), followed by recalibration.
However, unlike pure recalibration, band conversion would require a
bit of invasive surgery on the hardware, and this hw surgery would
need to be performed at a professional board assembly and rework shop.
If there is any serious interest, I can have a discussion with
Technotronix (the shop where our new FreeCalypso modem boards are
assembled) and see if they would be able to perform rework on Openmoko
devices, and how much they would charge for the service.  I won't be
adding any margin of my own on top of whatever Technotronix folks will
charge, but I would need to act as a middlewoman for logistics because
devices would need to be recalibrated after the SAW filter change, and
the calibration station with the CMU200 (a big, heavy and expensive
instrument) resides in my own lab, not at Technotronix.

Finally, if anyone has a FreeRunner that hasn't had the rework for bug
#1024 and is interested in getting that rework done, I can talk to
Technotronix about that rework as well - the hw surgery for bug #1024
rework and for the 900/850 band conversion involves the same shieldcan
over the GSM section of the motherboard, so both can be performed in
the same surgery.


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