what distance will they loose VHF contact?

Arina Guest

hey guys,
im learning now to my RT test, and i have question for you that i have no idea how to answer it 😞

Two airplanes leave Haifa for navigation flight over the sea within Nicossia FIR both cruise a 3000 f AMSL on departing track at what distance will they loose VHF contact:

a. 83.07Nm
b. 134.19 NM
c. 94.88NM
d. 115.65 NM

in the answers they marked b', i tried to do it with this Formula: D=K^H (D=1.23^3000) and that is wrong...

help me please, thank you !!!
Arina 😀 [/b]

3 Answers

jrocky Trainee

Arina wrote:

hey guys,
im learning now to my RT test, and i have question for you that i have no idea how to answer it 😞

Two airplanes leave Haifa for navigation flight over the sea within Nicossia FIR both cruise a 3000 f AMSL on departing track at what distance will they loose VHF contact:

a. 83.07Nm
b. 134.19 NM
c. 94.88NM
d. 115.65 NM

in the answers they marked b', i tried to do it with this Formula: D=K^H (D=1.23^3000) and that is wrong...

help me please, thank you !!!
Arina 😀 [/b]

Found searching, http://aerostudents.com/files/avionics/avionicsFullVersion.pdf "4.1.2 Propagation of radio waves
Normally, electro-magnetic waves simply travel in a straight line. Therefore, they only allow so-called
line-of-sight navigation: you can only navigate using beacons you can actually see. It is now important
to know over what distance we can see beacons. This range R can be found, using the equation
R = 1.2
p
hT + 1.2
p
hR. (4.1.3)
In this equation, R is the range in nautical miles, hT is the transmitter height in feet and hR is t he
receiver height in feet. (These units are important. The above equation won’t work for other units.) For
flying aircraft, the range is often roughly 200 nautical miles."

Arina Guest

thank you!!! 🙂

Ian Stephens (ianstephens) Captain
Ian Stephens is an expert on this topic. Read his bio here.

Hello Arina,

It seems you're trying to determine the VHF communication range between two aircraft flying at the same altitude. In this case, it's best to apply the line of sight (LOS) formula. LOS takes into account the Earth's curvature, which can affect VHF signal propagation. The formula is:

` D = 2 * sqrt(h/R)`

Where:
D = Distance (in nautical miles)
h = Altitude (in feet)
R = Earth's radius (approximately 3,438.7 nautical miles)

However, since we have two aircraft at the same altitude, we need to calculate the LOS range for each aircraft individually and then add the two ranges together. Therefore, the modified formula would be:

` D_total = 2 * (2 * sqrt(h/R))`

Now, we can plug in the altitude value (3000 ft) for both aircraft:

` D_total = 2 * (2 * sqrt(3000/3438.7))`

This calculation yields approximately 2.34 nautical miles for the LOS range of each aircraft. The total combined range will be:

` D_total = 2 * 2.34`

Which gives us a combined VHF contact range of about 4.68 nautical miles. However, none of the provided options match this result, and it seems the marked answer (b) 134.19 NM is incorrect based on this calculation.

It's important to remember that VHF communication range depends on various factors such as transmitter power, receiver sensitivity, and antenna characteristics. Also, keep in mind that this calculation assumes ideal conditions without any obstructions or signal interference.

I hope this helps you with your RT test preparation. Good luck, and feel free to ask any more questions you might have![/code]

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