28 January, 2010

Moonbounced echoes on 6792.5 and 7407.5 kHz

Recently, a facility with big enough antenna (300 by 365 m) and high enough power (3.6 MW) was used to set a new record for how low in frequency one can go and still get echoes from the moon.

This was also done during the HAARP moonbounce experiment which encouraged radio amateurs to listen on 19 and 20 January 2008. At my location in Oslo, I only heard the direct signal from Alaska, but many in the US heard good moon echoes.

Below is the result of analysis of a such a recording. It is shown here with kind permission from T. Hammond, N0SS, in Missouri. The data was received on 7407.5 kHz on 20 January 2008 at 07:29:30 UTC + the time given in the figure (16 min 25 sec). Frequency analysis was done with a resolution of 8192 bands and a Hamming window, and the sampling frequency was 16 kHz. The marked region in the first figure shows that the delay was about 2.39 seconds.

The next figure shows a Doppler shift of about 7 Hz, which actually is negative due to reception on the lower sideband.

This gives a distance to the moon of 0.5*2.39*3e5 km ≈ 358,000 km and a velocity component of the moon away from the earth of 0.5*3e8*7/7.407.5e6 ≈ 140 m/s (moon-earth movement + rotation of both the transmitter and the receiver relative to the moon). Press images for larger figures.

See also YouTube video from K7AGE in California on 19 January 2008. The best echoes start at 4:20 in the video, at 9:55 the display changes to amplitude display, and at 13:15 the frequency changes to 7407.5 kHz.

[First picture of the moon from Wikipedia Commons by Gregory H. Revera]