28 Jan
2014
28 Jan
'14
5:10 p.m.
On Tue, Jan 28, 2014 at 3:49 AM, Ralph A. Schmid, dk5ras
<ralph(a)schmid.xxx> wrote:
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.
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
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. 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.