How about a perfectly innocent scenario?

Before the war, a number of German-Americans (and one notorious
Swedish American aeronaut) supported the glorious ideals of the
Reich. It was perfectly legal, and in some neighborhoods, popular, to
be pro-German.

A German-surnamed gentleman, living in a prosperous neighborhood,
could easily have bought and operated a radio during the 'thirties.
Don't forget that German sympathizers regularly demonstrated in
American cities during the period. There was a lot of resentment
among German-American families about the ethnic cleansing that the
United States had imposed in 1917 against them.

As for hiding the antenna, I found exactly this kind of arrangement
in my own house. There was a shortwave antenna, just like the ones
you can buy at Radio Shack today, strung between the gable ends
(about 60 feet) and connected to a wire that had been fished into the
walls below. That would make a pretty fair shortwave reception.
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