[GreenKeys] Help to identify an old "SELCAL" circuit board

[jhhaynes at earthlink.net]

There was a company that made a number of products with that same form
factor - but I can't remember their name right now.  Their products
included an FSK converter, a board for controlling loops that involved
opto-isolators, and related products.  They were linked some way to Navy
MARS, which accords with those N call signs.  N call signs didn't come 
into general amateur use until later; back then they were used only by
Navy MARS.



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jhhaynes at earthlink dot net