Let Your Ears Have Wings

All VHF and UHF transmissions are essentially line-of-sight, and they don’t follow the curvature of the earth. This is the reason two stations only several hundred miles apart can use identical frequencies locally, without interfering with each other. Examples are SYDNEY TOWER and MELBOURNE TOWER, both transmitting on 120. 5 Mhz! UHF is much more ‘line-of-sight’ than VHF. The frequencies are much higher, the wavelengths are very much shorter. . . becoming microwaves. Aeronautical radio-telephony procedures are very strictly controlled. Transmissions are short as possible, and to the point. Ground stations are either manned by ATCs (air traffic controllers) or FIOs (flight information officers) from the FIS (flight information services) of the Department of Aviation.

Aircraft Flying in Uncontrolled Airspace

1. LIGHT AIRCRAFT (VFR): Visual flight rules.

2. LIGHT AIRCRAFT (IFR): Instrument flight rules.

3. Some APT (regular public transport) flights such as F-27, F-28.

4. Commuter airlines.

5. Some military flights.

6. Some international flights.

Understanding Vhf

118 to 136 Mhz has been allocated worldwide for air/ground COMMS. It is good usually up to 150 nm (nautical miles) unassisted but can be used over distances such as 600 nm or more if repeater stations are used to extend its available range. Repeaters are located on mountain tops in ideal terrain.

By way of example, in NSW, the Mt Oxley repeater at Bourke in the far north-west frequency of 128. 2 Mhz repeats 131. 3 and 118. 5 Mhz frequencies, used by traffic flying over the transcontinental northwestern routes. If you’re near the sea, and also near an international airport where aircraft commence their ocean crossings, you’ll hear the aircraft on VHF up to about 160 nm from the shore. The signals will quickly fade thereafter.

At 150 nm (oceanic), ATC will instruct pilots to tune HF primary and secondary frequencies, and the aircraft will abandon VHF and will operate thereafter on shortwave until it again nears a land mass.

Understanding Uhf

Usually good for communications (COMMS) up to 100 miles with aircraft. Its properties are very much like UHF but everything is much more exaggerated. For instance, UHF is very much more line-of-sight than VHF. UHF frequencies between 225 and 380 Mhz are used for military aviation. Airline companies use some of the thousands of frequencies in the UHF and UHF-T bands (450 to 500 Mhz) to conduct their airport ramp, catering, engineering and other operations.

Write to Us at Australian Aviation . . .

if you find this article on VHF/UHF aeronautical radio interesting and useful. If you didn’t catch Part 1, covering HF communications, featuring the exclusive worldwide HF frequency directory, we suggest that you obtain a back-copy. Just $4.00, from Aerospace Publications, Post Office Box 477, Manly 2095, NSW. Enjoy your monitoring!