Hi Michael,
Following my previous post I am herewith attaching two spectra of our capture and decoder program which are based on iio_utils and libiio respectively and where we note the spectrum based on iio_utils is better than libiio. We have integrated both iio_utils and libiio into to our decoder but we are not successful in decoding the packets yet. However, this part of decoder is tested separately and it decodes fine. The thing we are interested to know is the way the buffers are handled and what may lead to lost or miss-ordered samples/buffers. 
Many thanks in advance!
Mamatha & Mark