GSM850 downlink band SAW filter

Mychaela Falconia mychaela.falconia at gmail.com
Fri Nov 24 23:07:00 UTC 2017


Hello OsmocomBB community,

Now that the software issues have been solved with my obb-fcmods-r1
release, there is only one remaining feature of the historical Mot C1xx
phones that is not matched by the newly-made FCDEV3B product: support
for the GSM850 band.  Mot C1xx phones were made in 900+1800 MHz and
850+1900 MHz versions; my current FCDEV3B is 900/1800/1900 MHz triband,
but no 850 MHz band.

I could easily produce an 850/1800/1900 MHz version of the FCDEV3B if
I knew which SAW filter part number I should populate instead of the
EGSM downlink band B7820 filter which currently sits in the low band
Rx path.  But I don't know this part number.  I know that Openmoko
produced both 900/1800/1900 MHz and 850/1800/1900 MHz versions of
their GTA02 by populating different SAW filter parts onto the same PCB
footprint, but I only know the part number for the EGSM downlink band
filter (B7820, populated on current FCDEV3B boards), but not the one
for the GSM850 downlink band.

I looked at the schematics for a later quadband board from TI
(I-Sample, LoCosto chipset), but the SAW filters used there have a
different PCB footprint (smaller), hence their part won't work.

So, would anyone happen to know a part number for a GSM850 downlink
band SAW filter (be it the same one as used by Openmoko or a different
one) in the same physical package as the B7820, B7821 and B7851 for
EGSM, DCS and PCS downlink bands?

TIA,
Mychaela


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