[Milsurplus] I-81-A Radio Compass Indicator

[Boeing377]

All the radiocompass selsyn indicators I-81, I-82, MN-92 ( MN-92 is a rare lighted I-82) used with SCR 269 and ARN 7 run on about 26 VAC 400 hz. If you are using a square wave 400 hz source they will be very noisy (actually screechy) and a bit sluggish and jumpy. They run smooth and quiet on a pure harmonic free sine wave from a rotary inverter.

Funny how much radiocompass gear was bought surplus. I-82s in seemingly endless numbers show up serially on eBay. At a ham swap last month a guy had a bunch of brand new loop compensators and selsyns for the LP 21 loop antenna. They were too pricey ($30 each) and those things never ever wear out so I passed. 

That MC 203? loop compensator is a really ingenious piece of mechanical engineering. Nowadays you'd need shaft encoders, azimuth offset lookup tables and some software to accomplish the same thing.

73,
Mark
AF6IM
See photos from Pacificon 2010 Parachute Mobile jumps.
https://sites.google.com/site/boeing377/parachute-mobile-pacificon-2010-jumps



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