I'm trying to calculate the range of a VHF transmitter on an aircraft output power 50W, frequency 130MHz, and reciever sensitivity of -100dBm.

The calculations I have made give me ridiculously high numbers in the regions of thousands of Kilometres. The formula I used for this is as follows:

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Is there perhaps a different formula that I am not aware of?

  • $\begingroup$ Related: How do you calculate the maximum distance to communicate with tower control? $\endgroup$
    – user14897
    Sep 14, 2018 at 12:25
  • 1
    $\begingroup$ What are the values you're using for the rest of the variables? Gt and Pr would be needed to compute the R value. Is your wavelength in meters, or in what unit of measure? $\endgroup$ Sep 14, 2018 at 15:41
  • $\begingroup$ Antenna and recievers gain can be treated as negligible i.e. 1 in each case. The recieved power is -100dBm. I am getting crazy values when I utilise the above formula since -100dBm the lowest signap strenth that the reciever should pick up. But that translates into 0.1pW which then means ghe distances is far greater. How do I factor in line of sight and the curvature of the earth? $\endgroup$
    – Cyom
    Sep 14, 2018 at 15:43

1 Answer 1


VHF radio transmissions are primarily limited by line of sight. The formula for this is d = 1.23 * (√h1 + √h2) where h1 and h2 are the altitude s in feet, and d is the max range in miles.

  • 1
    $\begingroup$ This is a treshold distance. Beyond "d" you will not receive any signal (and this is true for frequencyes higher than atmosphear plasma resonance frequency). You can't calculate the received power using this equation. The power depends from the medium losses, the antenna qualities, the frequency and, of course, from distance. $\endgroup$ Sep 17, 2018 at 10:39

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