Moonbounce, radio signals bounced off of the moon





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Published on Jan 19, 2008

On the night of Jan 19 2008 at 05:00 UTC I heard signals bouncing off of the moon.

This was an experiment using the HF Active Auroral Research Program (HAARP) 3.6 MW transmitter system in Alaska, which can aim a lot of RF into the sky. At 05:00 they transmitted on 6.7925 MHz. The transmitter is on for 2 seconds and off for 3 seconds and repeated this cycle for an hour. The signal from Earth to Moon and back to Earth takes 2.7 seconds. So after the transmitter shuts off, if the signal is strong enough, we can hear the signal bouncing off of the moon. The signal strength was from 0 to about S3. The Alaska transmitter is heard at 30 over S9 at times.

I was able to hear signals bouncing off of the moon using my Kenwood TS-2000 with a 40 meter dipole up about 25 feet. Not bad DX.

Their calculation show that the power delivered at the terminals of a resonant 40 meter dipole antenna is 2.5 X 10-13 Watts or about -96 dBm. This is equivalent to about 4.4 microvolts across 70 ohms.

That is 2.5 billion watts. They had to re-aim the beam every 3 minutes at the moon.

Question in the comments, can you calculate the distance to the moon from the echo?


Looking at the signal at 10:28. I used the 2 second transmit time as a time-lenght reference. From the beginning of the transmission to the beginning of the echo, I measure 2.5 seconds, which is round trip time. So, 1.25 seconds one way. 1.25 seconds times 186,000 miles per second (radio wave speed) = 232,500 miles. Google shows 238,900 miles, average distance. Not bad using ruler measuring the signal on the computer screen.

ARRL Link:

HAARP Moon bounce Link:



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