Re: [Discuss-gnuradio] Format of captured data

[Karthik]

On Wed, May 27, 2009 at 9:18 PM, Firas Abbas <address@hidden> wrote:
>
> Hi,
>
>> On Wed, 5/27/09, Karthik <address@hidden> wrote:
>>
>> If you use usrp_c() source, then the real part of the complex values are the 
>> I values and the imaginary parts are Q values. They are each 16 bits.
>>
>> Karthik
>>
>
> That is not correct. If you use usrp_c source, then I & Q each are 32 bits 
> (total complex is 64bits). However, if you use usrp_s, then each are 16 bits 
> (total complex is 32bits)..
>
> Best Regards,
>
> Firas
>

Apologies for the wrong information. I don't mean to side track the
original query, but I have a couple of questions.

I found this in the FAQ.

"Regarding the bandwidth, we can sustain 32MB/sec across the USB. All
samples sent over the USB interface are in 16-bit signed integers in
IQ format, i.e. 16-bit I and 16-bit Q data (complex) which means 4
bytes per complex sample. This resulting in a (32MByte per sec/4Byte)
8Mega complex samples/sec across the USB."

So I guess here we are assuming that we are using usrp_s() ?

 Also, since the ADC only has 12bit precision, are the extra bits used
to retain precision as we go through the CIC and Halfband filters?

If I were to use the std_4rx_0tx.rbf and usrp_s() to receive 4
channels. Then am I correct in saying that I need to have a
deinterleaver with 8 channels after the usrp_s() from which I will
club channel 0 and 1 into a new complex stream (similarly for channel
2 and 3 etc) to get 4 complex streams?

Thanks,
Karthik