[ARC5] Radio Altimeter

[Bill Fuqua]

   The APN-1 always impressed me.
It is a very cleaver and simple radio altimeter using a wobbulator.
Now, some old times know what that is. I once had a  graduate student  from 
Poland come  to my office and
ask  for a wobbulator and the technical staff looked at him as if he was 
nuts, I said sure we have one
you may borrow. It was in the Polish to English dictionary he had. He 
borrowed it for a few days and
returned it.
    It had a Continuous FM  transmitter and a simple vacuum tube balanced 
mixer with an antenna
for each. The FM signal was sent to the ground and when the reflected 
signal returned it was
mixed with the output from the transmitter, by this time it would be at a 
slightly different frequency.
And this audio signal was amplified and its frequency measured with a 
simple analog frequency
meter. The difference frequency was proportional to the altitude.
   Later they went to pulsed systems. But as kid I was impressed by this 
simple but very
effective system.
73
Bill wa4lav