Visual Aural Range(VAR)
By the mid 1930's airlines were using planes such as the DC2 / Stinson / Lockheed 10 Electra. These fast high capacity [for their era] planes needed precise flight paths, especially for let downs in areas surrounded by mountains, such as
The radio range worked on the principle that a pilot could steer a precise course if he could listen to particular Morse letter codes. If the pilot flew the required preset course to a particular airport or waypoint, his heard a constant tone in his earphones. If left of track he heard the Morse letter "A" and the letter "N" if right of track. These preset course legs were published in the air navigation maps of the era.
The legs of the radio range can be aligned along particular airways, not just either 90' or 180' apart. The area directly over the transmitter was called the "Cone of Silence" as the signal fades in this area.
[USN Air Nav P.290]
The German Lorenz company's UHF 33 megacycle "4 Course Radio Range" radio beacons were at Brisbane / Kempsey / Sydney / Canberra / Holbrook / Melbourne / Nhill / Adelaide / Launceston / Hobart. [Job 1991; P.148]
Essendon's equipment was being tested by February 1938 while Archerfield's [Brisbane] installation was being tested by June 1938. [Job 1991 P.128]
The limit of reception for useful operation seemed to be about 70nm. [Job 1992; P.80]
By the early 1950's technology had developed the 4 Course Range into the Visual-Aural Range [VAR]. The system was now on the VHF120 megacycle band.
Beside the broadcast band improvement, the other change was the addition of the visual component.
One side of the visual leg displayed a blue indicator on the cockpit gauge while yellow was displayed on the other side. The pilot kept the needle in the middle of the gauge between the two coloured sides.
The aural Morse band could be on one leg of the range, eg 270’, while the visual signal could be on the crossing leg, eg 340’.
The VAR as depicted on the pilot's navigation chart showed
both the visual as well as the aural Morse legs. The blue / yellow visual legs
were shown with B [blue] or Y [yellow] for the appropriate side of the leg. The
aural Morse leg were shown with A or N for the appropriate side of the
Sydney was still a VAR based airport up to June 1960 at least.
The 1960's saw the addition of the VOR to the navigation aids on the Australian air routes. To avoid confusion the VOR was sometimes called the "omni".