29 Jan
2014
29 Jan
'14
8:23 a.m.
Hi,
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.
Yes, sure, this is normal behavior.
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
I see more problems in the receiver stages, and there parameters are also
mandatory during compliance tests.
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.
Of course, this is true, but do not forget the strong signals that come
backwards, from
other transmitters at a populated antenna site. Those can do nasty things in
the PAs,
so some filters and isolators can hardly be eliminated. A high power
wideband system
out in the wild is another beast than hooked to your lab setup.
-TT
Ralph.