[Milsurplus] ID ADF filter unit?

[Ian Wilson]

This is a box about 5"x2.5"x2.5" bearing the legend FILTER and a 5-position rotary switch. The switch positions are labeled ADF1(Voice,Range), BOTH, ADF2(Range,Voice).

There is yellow stencilled text on the back: T-2SC, and 5928. 10-pin connector on the rear.

A hand-written label states that this is a "1020Hz Accept/Reject Audio Filter".

Just found more stuff inside:
F-90/AIC
AF 33(600)-16647
Neptune Electronics Company

I'd be interested to know what this was part of, etc.

Thanks,

73, ian K3IMW