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Tom Tsou tom at tsou.ccHi Alexander, On Thu, Dec 22, 2016 at 6:37 AM, Alexander Chemeris <alexander.chemeris at gmail.com> wrote: > We're porting osmo-trx to our XTRX and we see some weird > constellation (https://goo.gl/photos/1KycUsv26Z6T6aN97). It looks like > a normal GMSK circle is there, but there is also a square like if a > signal is clipped. Do you have any idea what could cause this from > your previous experience? Squaring of the constellation is typically associated with overpowering some part of the chain. What does the spectrum look like? > We're running osmo-trx at 4 SPS. Then we double sample rate in > software (XTRX can't handle sample rates below 2 MSPS yet) and then > transmit. See first image above. > > Then we tried to increase sample rate and enabled 4x interpolation in > LMS7 - that led to a distorted cicrle + square constellation > (https://goo.gl/photos/zMZRecxmZsqiCYMHA). Again, check spectrum. Severe bandlimiting and overpower conditions will have visible spectrum effects. Also, the I/Q offset is high - consider offset tuning to remove DC and quadrature imbalance from the test scenario. -TT