What is the purpose of this RF sweep oscillator circuit section
Indeed, that's an odd diode arrangement.

It must be that L11 is coupled to the other 3 coils in that block otherwise L11 serves no purpose. The coupling might not be indicated in the schematic but I think that it must be coupled.

I am not that familiar with but did think: a diode mixer maybe ?

And indeed, see here



This is a double-balanced mixer and very similar to section C.

So I think it is a double-balanced mixer.

Section A: combining the double-balanced mixer with section A then A could generate the RF signal. Since it only has a supply connection that would make sense.

Right of C looks like an amplifier (signal goes to base of Q2) so that could be the IF output.