  The Korean VLBI Network (KVN) is a new mm-VLBI dedicated array with
capability for simultaneous observations at multiple frequencies, up to 129
GHz. The innovative multi-channel receivers present significant benefits for
astrometric measurements in the frequency domain. The aim of this work is to
verify the astrometric performance of the KVN using a comparative study with
the VLBA, a well established instrument. For that purpose, we carried out
nearly contemporaneous observations with the KVN and the VLBA, at 14/7 mm, in
April 2013. The KVN observations consisted of simultaneous dual frequency
observations, while the VLBA used fast frequency switching observations. We
used the Source Frequency Phase Referencing technique for the observational and
analysis strategy. We find that having simultaneous observations results in a
superior performance for compensation of all atmospheric terms in the
observables, in addition to offering other significant benefits for astrometric
analysis. We have compared the KVN astrometry measurements to those from the
VLBA. We find that the structure blending effects introduce dominant systematic
astrometric shifts and these need to be taken into account. We have tested
multiple analytical routes to characterize the impact of the low resolution
effects for extended sources in the astrometric measurements. The results from
the analysis of KVN and full VLBA datasets agree within 2-$\sigma$ of the
thermal error estimate. We interpret the discrepancy as arising from the
different resolutions. We find that the KVN provides astrometric results with
excellent agreement, within 1-$\sigma$, when compared to a VLBA configuration
which has a similar resolution. Therefore this comparative study verifies the
astrometric performance of KVN using SFPR at 14/7 mm, and validates the KVN as
an astrometric instrument.
