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A collection of thoughts, and my notes about experiments and ideas, technical or otherwise, connected to Amateur Radio, Satellite working and monitoring and other electronics.

Thursday, July 2, 2009

Lunar Reconnaissance Orbiter

The last week or two I have made an attempt to receive signals from the Lunar Reconnaissance Orbiter (LRO).

The LRO is currently in a polar orbit about 50km above the surface of the Moon, and has a transmitter on 2271.200MHz. It is possible to receive on Earth, as several people have done, already in it early days.

I decided to see if I could do this using "off the shelf" equipment with the antenna on a balcony.

I started my efforts using a handheld scanner , the AOR 8200 Mk3 which covers this frequency in SSB mode. Since I know that the sensitivity is insufficient on that frequency I started out using a LNA2227 (LNA), having a Noise Figure of less than 1.5 dB and finally a logarithmic-Periodic antenna (LPDA). no luck, but got a grid of "carriers" spaced about 215 Hz .... hmmm ... sounds like GSM.

After a few days I found myself digging out a WiFi grid dish with linear polarisation. still no results, and still GSM carriers.

Testing if this was Intermodulation Distortion (IMD) in my receiving system was done with a 10 dB attenuator ... the interference duly reduced by 10 dB, eliminating the suspicion of IMD in my system. I suspect two possibilities : Either IMD created somewhere outside my RX system or poor Image Rejection of the receiver. Most likely is the Image Rejection problem, since the GSM sidebands are strongest in the direction of a nearby base station.

Testing the connection between LNA and receiver revealed that the LNA had insufficient gain to overcome the high noise figure of the receiver, so what to do now ?

A quick test was set up using a satellite TV in-line amplifier, powered by a satellite receiver (off-the-shelf, remember). Still no success, but the noise performance was clearly better, as witnessed by other satellite signals in the 2.2 GHz band. Well, the moon was hidden by a tree at the moment of testing, making it difficult to point the antenna in the right direction. Still no signal from the LRO. I was beginning to doubt the usability of my system, but not yet giving up.

Finally, yesterday evening, the Moon was clearly visible, the antenna was pointed to the Moon, and bingo .... there was the signal ! A slanting line on the spectrogram showing a downwards change in Doppler shift.

Preliminary image 1 : http://www.xs4all.nl/~jgander/LRO1.jpg

I followed the signal till the LRO disappeared berhind the Moon, with the Doppler change getting much lower.

Preliminary image 2 : http://www.xs4all.nl/~jgander/LRO-gone.jpg

So - after a week of experimentation, finally success.

The receiving system need much more work, the first test will be making a filter that should (ideally) get rid of the GSM interference.

2 comments:

  1. congrats! nice first results!

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  2. Iam using the AR 8200 too, and watching the LRO signal as I type... cool stuff! Mike KG0UFO

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