[Milsurplus] Really Weird BFO

[Hubert Miller]

Dave, one of Bendix's post-war aircraft ADFs used the same system. I suppose maybe the idea was to cut out background noise, 
maybe similar to gated CW tone repeater projects that appeared in the ham magazines.  
Bendix issued later a bulletin on how to remove this circuit and replace it with a standard RF osc. BFO. Apparently not so good in real life use. 
I don't offhand recall the exact model, altho i have the manual and the modification bulletin somewhere. MN-28, maybe?
-Hue