Hackathon results: working Rx

Alexander Chemeris alexander.chemeris at gmail.com
Wed Sep 12 22:40:16 UTC 2012

Hi all,

Some good news for today. We've had a small fairwaves hackathon here
in Moscow and we've done a good progress in UmTRX development. I'm
quite exhausted, thus in short:

1. A software issue has been fixed in PLL tuning code. It works
reliably now. Previously it didn't correctly handle edge cases when
the best VCOCAP value was at the end of a range.
2. A software issue has been fixed in automatic LMS calibration code.
Turns out a process described in the datasheet is not complete - you
have read FAQ, question 4.7 for an amendment.
3. Now we correctly select Rx input. You have to change _two_
registers to do that - 0x75 and 0x25. This wasn't obvious from the
brief reading of the manual.
4. A hardware bug was fixed - RF diversity switch required a bias to
work correctly. Luckily we decided to move the switch from the main
board to a frontend in the rev2 of UmTRX. So we don't have to re-make
the UmTRX schematics.

Huge thanks to Andrey Sviyazov ("RF guy"), Andrew Karpenkov ("FPGA
guy") and Srdjan Milenkovic ("remote LimeMicro guy") for going through
all the issues.

Fixes for the code will be pushed to github in the next few days after
I clean it up.

PS Another good news is that we should have first UmTRXv2 units on
hands in the next few days, when we get them from customs. Can't wait
to put my hands on them.

Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио

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