[USRP-users] SBX daughtercard bandwidth problem..!!

salman dinani salmandinani at gmail.com
Sun Feb 12 01:03:47 EST 2012


Hi to all,

I am using USRP N200 with daughtercard SBX by MATLAB R2011b..I am running
the card quite well and transmiitting and receiving signals correctly..but
i have come across a very annoying problem..It is wriitten in " *UHD -
Daughterboard Application Notes "* on
http://files.ettus.com/uhd_docs/manual/html/dboards.html that the bandwidth
of the SBX daughtercard is 40 MHz..but my daughtercard only transmit and
receive signals correctly only upto 12 MHz..(I have verified the
transmitted signals on spectrum analyzer, signals having BW or frequencies
above center freq  more than 12MHz dont get received)..i dont know why it
is like that..after investigating a bit i found out that:

The SDRu block in Smiulink ask for the following parameters:

Centre Freq
LO offset
Decimation(or interpolation)

The sample rate of the USRP is 100e6 and the sample RF front end is set by
the following formula: RF_sample rate =100e6/decimation..

what i have observed is that the lowest possible decimatiom factor is 4..!!
I write value of decimation "1" in desired value in order to get the full
sample rate of 100e6, it shows 4 in device value..This means

100e6/4=25e6...

so if it is so then it would sample waves up to 12 MHz only..and it is very
disappointing..please tell me:

1. Am i write in this conclusion??
2. If yes, than why it is written in application notes tat it has BW of 40
MHz??
3. If no, than why am i not able to get wave sampled of BW 40MHz?
4. Why i am not able to set decimation or interpolation to 1.??

Regards

Salman Dinani
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