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Tom Tsou tom at tsou.ccOn Tue, Jan 28, 2014 at 3:49 AM, Ralph A. Schmid, dk5ras <ralph at schmid.xxx> wrote: >> N-th harmonic of what? > > Of the RF carrier. I guess there will be some harmonics, and I will have a > look > what my WBX produces if you are interested. Note that the USRP1-WBX combination does not support LO offset or IQ imbalance compensation; those factors will be your largest source of overall signal distortion. In regards to the harmonic distortion, it seems that the concern is over spurious free dynamic range (SFDR) of front end components, which is more of an issue of wideband RF design than SDR in general. Similar issues can exist in any wireless system - SDR or not. >> More recent devices are based on flexible integrated RF chips from Analog >> Devices and Lime Micro that were specifically designed for commercial 3G >> and 4G systems. I find it hard to believe that these SDR products are not >> capable of passing international compliance requirements for GSM. > > Usually there is even for those low power applications some passband filter > in the output path. I will certainly not deny that spurious signals exist in USRP-type boards or that passband filters are used in commercial products. My only issue is the claim that a narrow tuning range limited by front end filters is a mandatory requirement for suitable spectrum compliance. A huge number of frequency bands is required by current and future wireless services and attaching a fixed RF filter for every individual band in use is not a sustainable approach. There has been a very significant amount of development in flexible RF design over the past decade in order to address these issues, which I do not think should be ignored. -TT