Chapter 9. Q & A
9-7
Q36. Please tell me about communication range?
Below graph is to help you figure out the electric field intensity within a range
of h1(10 m) and h2(the height of the other ship) when the signal is transmitted
with 144 MHz and 10 W.
How to figure that out is:
For example, let’s say that if the height of the antenna on your own ship is 10 m
high and other’s within 10~30 m, the point where the X-axis of the line with the
minimum electric field intensity of +6 dB and the height of the other ship’s
antenna, let’s say 20 m high for example, intersects is the RX distance in
question here. However, make sure to shift the curve upward by 3 dB.
Therefore, we can confirm from below graph that 50~70 km (26~38 NM) is the
VHF’s communication range and signals outside of it will be considered to be
abnormally propagated signals.
+6 dB
e.g. Other ship’s
antenna is 20 m.
Communication distance to find
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