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Contamination due to foregrounds (Galactic and Extra-galactic), calibrationerrors and ionospheric effects pose major challenges in detection of the cosmic21 cm signal in various Epoch of Reionization (EoR) experiments. We present theresults of a pilot study of a field centered on 3C196 using LOFAR Low Band(56-70 MHz) observations, where we quantify various wide field and calibrationeffects such as gain errors, polarized foregrounds, and ionospheric effects. Weobserve a `pitchfork' structure in the 2D power spectrum of the polarizedintensity in delay-baseline space, which leaks into the modes beyond theinstrumental horizon (EoR/CD window). We show that this structure largelyarises due to strong instrumental polarization leakage ($\sim30\%$) towards{Cas\,A} ($\sim21$ kJy at 81 MHz, brightest source in northern sky), which isfar away from primary field of view. We measure an extremely small ionosphericdiffractive scale ($r_{\text{diff}} \approx 430$ m at 60 MHz) towards {Cas\,A}resembling pure Kolmogorov turbulence compared to $r_{\text{diff}} \sim3 - 20$km towards zenith at 150 MHz for typical ionospheric conditions. This is one ofthe smallest diffractive scales ever measured at these frequencies. Our workprovides insights in understanding the nature of aforementioned effects andmitigating them in future Cosmic Dawn observations (e.g. with SKA-low and HERA)in the same frequency window.

Wide-field LOFAR-LBA power-spectra analyses: Impact of calibration, polarization leakage and ionosphere