A long standing problem in the study of Active Galactic Nuclei (AGNs) is that the observed VLBI core is in fact a blending of the actual AGN core (classically defined by the  = 1 surface) and the upstream regions of the jet or optically thin flows. This blending may cause some biases in the observ- ables of the core, such as its flux density, size or brightness temperature, which may lead to misleading interpretation of the derived quantities and physics. We study the effects of such blending under the view of the Korean VLBI Network (KVN) for a sample of AGNs at 43 GHz by comparing their observed properties with observations obtained using the Very Large Baseline Array (VLBA). Our results suggest that the observed core sizes are a factor  11 larger than these of VLBA, which is similar to the factor expected by considering the different resolutions of the two facilities. We suggest the use of this factor to consider blending effects in KVN measurements. Other parameters, such as flux density or brightness temperature, seem to possess a more complicated dependence.

Abstract
1. INTRODUCTION
2. OBSERVATIONS
    2.1. Data Selection Criteria
    2.2. The Data
3. RESULTS
    3.1. Notes on Individual Sources
4. DISCUSSION
    4.1. Origin of the Dispersion in fS and fd
    4.2. Extrapolation to Other Frequencies
5. CONCLUSIONS
REFERENCES

• Juan-Carlos Algaba(Department of Physics, Faculty of Science, University of Malaya/Department of Physics and Astronomy, Seoul National University) Corresponding author
• Jeffrey Hodgson(Korea Astronomy and Space Science Institute)
• Sin-Cheol Kang(Korea Astronomy and Space Science Institute/Korea University of Science and Technology)
• Dae-Won Kim(Department of Physics and Astronomy, Seoul National University)
• Jae-Young Kim(Max-Planck-Institut f¨ur Radioastronomie)
• Jee Won Lee(Korea Astronomy and Space Science Institute)
• Sang-Sung Lee(Korea Astronomy and Space Science Institute/Korea University of Science and Technology)
• Sascha Trippe(Department of Physics and Astronomy, Seoul National University)