Originally Posted by
treadigraph
Looking at the cockpit glazing there are three with one design (and some sort of black bulge: ADF loop?) and three with a different design.
Yes, the black bulge is an ADF loop.
Anson photos on the 'Net don't seems to show any consistent differences between the C.19 and T.21 - some have no ADF loop at all, some have one just behind the cockpit roof glazing (both as in the photo) and some have the ADF loop further aft with an astrodome forward of it.