What is the attenuation caused by the environment?

The background noise at VHF is much more important when we place the antenna vertically. It is because most of the interference sources radiate vertically and, unfortunately, it is often the best position to receive a transmitter signal with the maximum strength. So, frequently, it is advisable to place the receiver’s antenna in a position neither vertical nor horizontal in order to lessen, as much as possible, the background noise with the minimum loss of useful signal.

It has happen that an animal has hidden itself in a big city carrying a VHF transmitter and it has been so difficult to track and find this animal because of the interferences. In these cases, it is advisable to check a searching technique called back-interference method. (How can I avoid interferences?).

When a fast animal, such as a bird of prey, chases a target, it can fly extremely quickly and, if we are not properly located (in a high place with good visibility), we could not receive the signal in the best condition. This fact might cause a misunderstanding and we may walk toward the opposite direction. If this happen, we should look for the highest position even if we go away a little bit. Signals may be very weak and the background sound measured in different situations and places is from 10 to 400 times the minimum signal that a receiver picks up at VHF -what means that the signal will not be properly received. This problem is less important at UHF.


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