The old Four-Course Radio Range depended on the fact that two AM signals
on the same frequency mix linearly. Off course one way, the pilot heard
primarily an "N". Off course the other, primarily an "A". On course,
the two covered each other and he heard a steady tone. It is extremely
sensitive, you didn't have to be very far off course before you began to
hear the letter faintly under the tone. The other huge advantage was it
required only an AM radio and headphones in the aircraft.
CONSOL, a 30's/early 40's aircraft nav system is another example.
Fairly complex phased antennas on the ground. In the airplane, all the
navigator had to do was count the number of dots he heard before they
merged into a tone, and then look on a chart to determine his bearing to
the station. Again, just an AM receiver. CONSOL was used by both the
German and Allied air forces, possibly the only such system ever. The
Allied planes used it to compute the winds crossing the Channel before
they reached the coastline.
Old isn't always crude. I've never transmitted AM with my K3, I don't
have the filter(s), but it works with WWV.
73,
Fred K6DGW
- Northern California Contest Club
- CU in the 2013 Cal QSO Party 5-6 Oct 2013
- www.cqp.org
On 1/29/2013 1:58 PM, NZ0T wrote:
Nate, that is exactly the reason AM is still used for aviation.
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