Multiple DDC chains on UMTRX

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John Wilson john.wilson at pathintelligence.com
Mon Apr 22 08:14:57 UTC 2013


Hello,

I was wondering whether there is an FPGA image for the UmTRX which gives 4x
DDC Rx chains (at the expense of the two DUC chains) like the USRP1
usrp1_fpga_4rx.rbf. I guess this is unlikely, due to the fact it looks like
the majority of people are using the UmTRX for OpenBTS! How difficult would
it be to change the current firmware to support this.

Another couple of questions, what's the maximum achievable bandwidth
through a single Rx chain so far and are there any constraints on what
value of decimation to use (e.g. USRP has the requirement that to use both
CIC filters decimation factors have to be a factor of 4, otherwise the
frequency response will be affected)? When I increase the sample rate (e.g.
4.333 MHz) I start seeing the frequency response affected, the FFT plot
seems to 'flicker' between a reasonably flat looking response and a poor
frequency response (see attached files - both taken from the same running
instance of a flow graph)

Cheers,

John

-- 
*Dr. John Wilson*
Product development engineer, Path
Intelligence<http://www.pathintelligence.com/>
T +44 2392 388442    @pathintel
DETECT • ANALYSE • PREDICT • INFLUENCE


Path Intelligence Limited, registered number 5176274. Registered in
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