According to the post from Robert, it seems that 621 comes from the directional MW antenna (заря).
Does 1548 also come from that?
If it is a directional signal, it might come from the 4 mast ARRT array (квадрат). These are quite interesting.
Look at the feeder lines, they go further than the antenna. I don’t know the reason for that yet.
Radioens reports that Vesti FM (вести фм) 1413 kHz uses this 4 mast ARRT directional antenna.
MWlist points to an non-directional mast without a ARRT cage antenna.