[MRCA] Identify Strange Item

[Doran Platt]

My friend brought over a piece of gear that I cannot identify, nor fathom its actual end use.  He picked this, and an Eico novice tx at a junk store. Its is nomenclatured as "Transistorized Channel Selector" and apparently mfg by NSA's lab.  AC powered, 8 1/2" high rack mount assy.  It has a 5 band, slide-rule dial assembly not unlike an Eddystone or National (but not). The 5 bands go from 0-100 kHz.  It has a BFO selector USB, LSB, and AM, input and output gain conbtrols and a.c. power switch.  No other controls.  There is a nice schematic inside that tells it all... if one knew what it was really used for.  It has a single LPF input via 1/4" phone jacks. There is a 5 band LO going to a balanced mixer, thence to a Collins 455 mech filter.  Signal then goes thru a 455 kHz strip, a diode detector and crystal controlled BFO for USB and LSB.  Again, no front-end gain, no AVC, or pre-selection.  Input sensitivity to get a usable signal in the headphones is above perhaps .1v Anyone have any idea?  Maybe a back end for a VLF receiver system?
Jeep K3HVG
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