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Eco from the Moon

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Linas

Fri Oct 22 2010, 05:11PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

HI, does any one know how to get the eco from the moon ? ( i need to measure distance to the moon)
I can only think about magnetron sending focused signal, and some how measuring with high speed oscilloscope resonance on LC circuit which is tuned with magnetron Fo.
Does any one have better and maybe simple idea ?

Proud Mary

Fri Oct 22 2010, 05:34PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Laser reflectors left on the lunar surface by the Russian Lunokhod 2 and the American Apollo 15 missions are still functioning, and used for daily monitoring of the Earth-Moon distance.

Some radio hams communicate by using the Moon to reflect UHF signals back to earth.

Sulaiman

Fri Oct 22 2010, 05:40PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Do you have a license to transmit ?

If not then you'll need a powerful laser, telescope and detector.

Linas

Fri Oct 22 2010, 05:47PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

ok, if we talking about lasers, how many power did i need?

So with magnetron i will send 60db and receive -157
so i can measure it, now just question how ?

Proud Mary

Fri Oct 22 2010, 06:18PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Linas wrote ...

ok, if we talking about lasers, how many power did i need?

So with magnetron i will send 60db and receive -157
so i can measure it, now just question how ?

You need a large telescope - large by amateur standards - a 1.5m mirror - just to align the laser on the reflector. Then you need an even larger telescope to capture the returning pulse which may consist of only one photon.

Stick your chops into the Apache Point Observatory Lunar Laser-ranging Operation here:

This picture shows the terrible lonely journey of Lunokhod 2 across the desolate surface of the moon, and the final resting place of its laser reflector, where it remains to this day, a ghost of the Soviet Empire:

1287771301 543 FT0 Lunokhod 2 Tracks Final

Linas

Fri Oct 29 2010, 08:40PM

Registered Member #1143 Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721

I see lot of videos in youtube that people can transmit sound and receive it and quite well , it 's called EME.

I get 400Wrms 9KV 7,4A peak Russian tube so i can transmit signal to the moon with high gain antenna, now just question left which frequency should i use ? 144MHz, 450MHz or 1,3GHz? (tube is up to 3GHz)
and also i need get at least 10W before tube amp ( that would be 20-80V amplitude driving signal), and still don't know how

Proud Mary

Sat Oct 30 2010, 12:08PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I have the impression that timing the return signal from our Moon with sufficient accuracy to calculate distance would require a rubidium standard or hydrogen maser clock.

And you can bet that all sorts of corrections have to be applied to the raw data too.

An old clockwork pocket watch used for timing horse races simply will not do!

...

Sat Oct 30 2010, 05:56PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

If you can get your hands on a q-switched Nd:YAG laser and a a pmt with a tight bandpass filter at 1064nm (or 532nm if you have a 532nm laser), it should be possible to get a bounce of the moon using a telescope as a beam expander.

You do not really need to worry about hitting the mirror head on, your beam will be huge by the time it hits the moon anyway. You also don't need to worry about the timing all that much, the round trip time is about 3s, you could use your computers sound card and get 4-5 sig figs.

Sulaiman

Wed Nov 17 2010, 01:20PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Using radio at 450 MHz the path loss budget is about 220 to 250 dB for EME.
That requires a low noise receiver, a very good antenna, and lots of rf power.
I'm not at that level yet.

Proud Mary

Wed Nov 17 2010, 02:23PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

... wrote ...

You do not really need to worry about hitting the mirror head on, your beam will be huge by the time it hits the moon anyway. You also don't need to worry about the timing all that much, the round trip time is about 3s, you could use your computers sound card and get 4-5 sig figs.

If only the astronomers at Apache Point Observatory Lunar Laser-ranging Operation had your brains, just think of the time and money that could be saved!

With all their costly equipment, and PhDs bought by the mile, they still seem to be having difficulties:

Lots of things have to be working just right to get photons back from the lunar reflectors. The laser beam has to be very well collimated. The laser beam must be pointing precisely at the reflectorâ€”which cannot be seen directly, so it's a blind pointing. The detector must also be looking at the exact spot on the moon corresponding to the reflector. This is independent from the laser pointing, so not guaranteed to be bang-on even if the laser is. Now the moon (when illuminated) is very bright. And we're looking for a mere few photons from the reflector. But we know the wavelength of the laser, and can let only that color light into the detector. We also know where on the moon the light is coming from, so we can reject all moonlight except for that right around the reflector. And most importantly, we know when to expect the laser pulse to return, to few-nanosecond precision, typically. So we only turn on our detector for 100 nanoseconds (100 billionths of a second) around the expected time. We can schedule this to nanosecond precision. We have about 50 shots on the way to or from the moon at any time, so we have a "schedule book" telling our equipment when to open up the detector. Imagine trying to keep your personal calendar commitments to nanosecond precision!

Extracted from "The Basics of Lunar Ranging"

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