To communicate over the longest distances hams use moon bounce. VHF signals normally escape the Earth's atmosphere, so using the moon as a target is quite practical. Due to the distance involved and the very high path loss getting a readable signal bounced off the moon involves high power ~ 1000 watts and steerable high gain antennas. Receiving these very weak return signals, again involves the use of high gain antennas (usually the same ones used to transmit the signal) and a very low-noise front end RF amplifier and a frequency stable receiver. However, new and recent technological advances in weak signal detection has allowed the successful reception of signals off the moon using much smaller or less well equipped stations allowing reception of signals that are "in the noise" and not audible to the human ear. One of these modes is JT65 which is a digital mode. Due to the delay of the signal traveling to the moon and back (travel time approx. 2.5 seconds), a person transmitting may hear the end of his own transmission returning.
Some pics of recent full moon at Chennai on 6th March Friday.
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