[Elecraft] The Old Days

[Fred Jensen]

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.