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I have experienced several times that heavy rain seems to jam the signal a radio of a bus receives. The only explanation I have is that the rain drops also become weak emitters, if a radio wave hits the rain drop. The stronger the noise, the lower the SNR becomes.

I had another thought, in which the frequency of the signal is altered depending on the density of the rain in the air. I would ignore the distance from emitter to receiver as it should be about the same all the time. At least as long as you are not moving directly towards or away from it. I don't really understand what process is happening there, so I would be very happy, if someone could help me.

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  • $\begingroup$ i think it has to do with attenuation . $\endgroup$ – Gowtham Dec 19 '14 at 13:50
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    $\begingroup$ Raindrops are made of water, which has a significantly larger dielectric constant than air. The presence of heavy rain makes the space between the transmitter and receiver appear like an inhomogeneous medium. This leads to scattering (just like the much smaller droplets of fog scatter visible light). As a result the there is an additional power loss between transmitter and receiver. $\endgroup$ – CuriousOne Dec 19 '14 at 14:15
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Electric fields created in storm clouds could also be a contributing factor in interfering with your radio, a small field created by my bathroom fan constantly interferes with with my tv signal and it drives me mad.

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Attenuation due to rain is a major issue for signals at frequencies above 10 GHz, and is noticeable at frequencies above about 1GHz, but if you're talking about broadcast FM radio (~100 MHz), or most common kinds of two-way radios (~50MHz, ~150MHz, ~450MHz, or ~900MHz), then rain fade is too small of an effect to notice. The water droplets in clouds are simply not big enough to interact much with lower-frequency signals.

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