Listening to Art Bell tonight and he related an incident where he heard his own 80 meter signal come back 3-4 seconds after transmitting. While the distance to the moon and back is about right for that, generally moon bounce requires full legal powers, high gain antennas and frequencies much higher so that they penetrate the ionosphere, and even then voice is almost impossible, only narrow band Morse code which is very narrow bandwidth, is generally usable. More over, the echo was a 20db over S9 signal not just above the noise threshold barely as you would expect with moon bounce.
He tuned his transmitter up and down to make sure it wasn’t just someone sending it back to him somehow and it followed.
I have also experienced this phenomena, but not as long of a delay and on 1200 Khz. Back before 1210 Khz was in local use, I operated a pirate radio station on 1200 Khz, this was back in the mid 1970’s. I had a radio to monitor our transmission in the studio. One night when I signed off I heard the last second or so of our transmission after I cut the transmitter power. A second at the speed of light is 186,000 miles, we were lucky if our signal reached 20 miles.
I have read of many accounts of this phenomena, some with delays as long as 15 seconds. I’ve yet to read a reasonable explanation. The Wikipedia contains five theories, but none of them seem to account reasonably for the typically very strong signal strength of these echoes.
I’m fascinated by these because I wonder if they aren’t tickling a much more exotic phenomena such as portals or some oddness in time. All the theories given on the Wikipedia don’t seem to account for the signal strength of some of these phenomena.
All of the incidents I’ve heard of have been relatively low frequency, 80 meter, 160 meter, AM broadcast band, but the Wikipedia documents cases at 432 Mhz and 1296 Mhz.
Having been interested in TV and radio DXing for many years, I will note that there are many rare but interesting forms of propagation. Even at optical frequencies interesting things occur. One of the photos I use in my headers has a ship floating up in the sky. Obviously the ship wasn’t really in the sky but differences in the density of the air bent the light reflection to make it appear so. The same things and many others happen at radio frequencies. So it might be something ordinary but at present unknown. I find it fascinating none the less.