[Milsurplus] Re: BC-733 an iron radio

[C. Whitaker]

de WB2CPN
As far as I know the basic blind landing systems
were developed by Bendix at Teterboro Airport
in New Jersey, and that was a long time ago. 
For ILS, the Azimuth Guidance system was developed
first.  The Vertical Guidance info came later when
technology had advanced somewhat.   I have spent
lots of time on the innards of the SCS-51, the AN/MRN-7
and AN/MRN-8, the CAA Localizer which was
used during the late 40's, and the CAA VAR range.
(But not the CAA Glide Path equipment.)  The basic idea
was to radiate a VHF carrier signal down the runway center
line toward the approaching aircraft, then apply 90 Hz
amplitude modulation to the signal which was on one side of
the approach line (runway), and apply 150 Hz amplitude
modulation to the signal which was on the other side of the
approach line.  These little audio frequencies have a 3/5
ratio which prevents their harmonics from interfering with
each other.  The Localizer is located at the far end from
touchdown.   The antenna was a collinear array made of
approximately 13 horizontal dipoles, (or Alfred Loops),
which were lined up across the center line.  The carrier
frequency was fed into all the dipoles, the two sidebands
were each fed to the dipoles on their respective sides.
One additional antenna collocated with the course array,
but separate, radiated  90/150 information toward both
sides of the runway, and for some distance in all directions.
Pilots could fly the "back course", but it was not as
sensitive as the main course.  This was the "clearance
array".     TRIVIA    Anyone want to hear about how
the Glide Path system came to be?
73  Clete



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