[GreenKeys] Polar Relays

[Jim Haynes]

It's good to see all this interest in historical artifacts like polar
relays.  However they were not all that popular for RTTY.

Some early demodulators, and this goes all the way back to the 1920s
(U.S. Patent 1,705,211).  The mark frequency detector went to one
winding of the polar relay and the space detector went to the other.
So the decision of whether the signal was mark or space was made right
in the relay itself.  In amateur use the W2PAT converter was published
in January 1953 QST, page 44.  And the W2JAV converter was similar.

Later on polar relays fell into disfavor because they added a mechanical
element that required adjustment.  I remember a cover of RTTY magazine,
May 1963 issue with a cartoon coat-of-arms "Knights of the Mark Three"
showing a polar relay being assaulted with an axe.  Mark Three was a
converter designed by the great RTTYer W6NRM.  Driving the selector magnet
directly from a tube, and later from a transistor, became the norm.
The mark/space decision was made elsewhere in the demodulator.  Polar
relays also disappeared from commercial and military designs.

Polar relays built into the machine were always optional, needed if
the machine had to receive polar signals or operate on low line currents.
These are all conditions connected with wire-line circuits, not radio
or local loops.

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 	"Ya can argue all ya wanna, but it's dif'rent than it was."
 	"No it ain't! No it ain't!  But ya gotta know the territory."
 		Meredith Willson, The Music Man