# How did four-course LF radio navigation ranges have their beams other than at 90° / 180° angles?

The four-course Low Frequency Radio Range system used for aircraft navigation (in the US and elsewhere) in the 1930s and 1940s used a pair of directional antenna (with figure-of-8 shaped radiation patterns) at 90 degrees to each other. One antenna would transmit the Morse code pattern for "A" (⋅-) and the other for "N" (-⋅), as follows:

When the aircraft was on course, the signals from the "A" transmitter and the "N" transmitter would be at equal value and overlap to form a continuous tone:

If the antenna patterns are at 90° and the transmitted power is the same for the two signals then the system provides four different courses that a plane could fly (or eight, counting reciprocal courses away from the station).

Examining charts for actual installations, however, one often sees that the four courses are not at 90° angles:

How was this in practice achieved? I can see that by increasing the relative strength of one transmitter compared to the other the courses could be adjusted so they crossed at other than a right angle (like this, for the top diagram, supposing A is stronger than N):

\ N /
\ /
A X A
/ \
/ N \


But how would it be arranged to have asymmetrical patterns such as the one in the Stout Field diagram above, where the opposing courses are not at 180° angles to each other?

• I have a working 4 course radio range at my private airport. You can "crow's foot" a radio range by changing the RF phase of the antennas. Plus you can shift the courses by 90 degrees using a RF Goniometer. I use my radio range for real flying.
– user117685
Jul 25, 2016 at 2:30
• @Davidfrantz: by changing the phase of one pair with respect to the other pair, or of one antenna within a pair with respect to the other? Aug 2, 2016 at 22:55