ORIGINAL: Dave
JOHN SOHM IS ABSOLUTELY RIGHT. (Post # 304)
The 2.4GHz wavelength is directional. Since we can not focus a high gain directional parabolic dish antenna
between our constantly moving model airplane and our transmitter, we have to use an omnidirectional vertical
antenna system which has much lower signal intensity. Since we have to use an omnidirectional antenna system,
the electromagnetic waves will scatter and diffract from objects and from the terrain around us. When the diffracted
wave reaches the receiver antenna, it is slightly lags behind the signal which traveled to the receiver antenna in a
straight line that creates interference due to the phase canceling effect.
Dave,
This fails to take into account the digital nature of our 2.4 systems and the inherent error correction digital systems use. Digital systems use a packetized transmission protocal, so every signal is numbered and when the Rx receives a second signal with the same number of a previously received signal (the slightly delayed reflected signal), that command is ignored. Additionally, phase cancelling effect only works if it's 180 degrees out of phase, which is very, very rarely the case for randomly reflected signals.
Also, yes, omni antennas exhibit spherical spreading losses, but "signal intensity" is not that important a value, signal to noise ratio (SNR) is the important value. Who cares if the Rx receives 10,000 watts or 10 MW, as long as the received signal is higher than the "noise" the Rx knows what to do.